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A genetic disorder is a health problem caused by one or more abnormalities in the
genome In the fields of molecular biology Molecular biology is the branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, M ...

genome
. It can be caused by a
mutation In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechan ...
in a single
gene In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mecha ...

gene
(monogenic) or multiple genes (polygenic) or by a
chromosomal abnormality A chromosome abnormality, chromosomal anomaly, chromosomal aberration, chromosomal mutation, or chromosomal disorder, is a missing, extra, or irregular portion of chromosomal DNA. These can occur in the form of numerical abnormalities, where there i ...
. Although polygenic disorders are the most common, the term is mostly used when discussing disorders with a single genetic cause, either in a gene or
chromosome A chromosome is a long DNA molecule with part or all of the genome, genetic material of an organism. Most eukaryotic chromosomes include packaging proteins called histones which, aided by Chaperone (protein), chaperone proteins, bind to and ...

chromosome
. The mutation responsible can occur spontaneously before
embryonic development An embryo is the early stage of development of a multicellular organism A multicellular organism is an organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms ar ...
(a ''de novo'' mutation), or it can be
inherited
inherited
from two parents who are carriers of a faulty gene (
autosomal recessive In genetics Genetics is a branch of biology concerned with the study of genes, genetic variation, and heredity in organisms.Hartl D, Jones E (2005) Though heredity had been observed for millennia, Gregor Mendel, Moravia, Moravian scientist ...

autosomal recessive
inheritance) or from a parent with the disorder (
autosomal dominant In genetics, dominance is the phenomenon of one variant (allele) of a gene on a chromosome masking or overriding the Phenotype, effect of a different variant of the same gene on Homologous chromosome, the other copy of the chromosome. The first ...

autosomal dominant
inheritance). When the genetic disorder is inherited from one or both parents, it is also classified as a hereditary disease. Some disorders are caused by a mutation on the
X chromosome The X chromosome is one of the two sex-determining chromosome A chromosome is a long DNA Deoxyribonucleic acid (; DNA) is a molecule File:Pentacene on Ni(111) STM.jpg, A scanning tunneling microscopy image of pentacene molecul ...

X chromosome
and have
X-linked Sex linkage describes the sex-specific patterns of inheritance Inheritance is the practice of passing on private property, titles A title is one or more words used before or after a person's name, in certain contexts. It may signify eithe ...
inheritance. Very few disorders are inherited on the
Y chromosome The Y chromosome is one of two sex chromosomes (allosomes) in therian mammals, including humans, and many other animals. The other is the X chromosome. Y is normally the Sex chromosome#Sex determination, sex-determining chromosome in many species, s ...
or
mitochondrial DNA Mitochondrial DNA (mtDNA or mDNA) is the DNA Deoxyribonucleic acid (; DNA) is a molecule File:Pentacene on Ni(111) STM.jpg, A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of five car ...
(due to their size). There are well over 6,000 known genetic disorders, and new genetic disorders are constantly being described in medical literature. More than 600 genetic disorders are treatable. Around 1 in 50 people are affected by a known single-gene disorder, while around 1 in 263 are affected by a
chromosomal disorder A chromosome abnormality, chromosomal anomaly, chromosomal aberration, chromosomal mutation, or chromosomal disorder, is a missing, extra, or irregular portion of chromosomal DNA. These can occur in the form of numerical abnormalities, where there i ...
. Around 65% of people have some kind of health problem as a result of congenital genetic mutations. Due to the significantly large number of genetic disorders, approximately 1 in 21 people are affected by a genetic disorder classified as "
rare Rare may refer to: * Rare, a particular Doneness, temperature of meat * Something infrequent or scarce, see Scarcity :* Rare species, a conservation category in biology designating the scarcity of an organism and implying a threat to its viability ...
" (usually defined as affecting less than 1 in 2,000 people). Most genetic disorders are rare in themselves. Genetic disorders are present before birth, and some genetic disorders produce
birth defect A birth defect, also known as a congenital disorder, is a condition present at birth Birth is the act or process of bearing or bringing forth offspring, also referred to in technical contexts as parturition. In mammals, the process is initiat ...
s, but birth defects can also be
developmental Development of the human body is the process of growth to maturity. The process begins with fertilization Fertilisation or fertilization (see spelling differences), also known as generative fertilisation, syngamy and impregnation, is the ...
rather than
hereditary Heredity, also called inheritance or biological inheritance, is the passing on of traits Trait may refer to: * Phenotypic trait in biology, which involve genes and characteristics of organisms * Trait (computer programming), a model for str ...

hereditary
. The opposite of a hereditary disease is an . Most
cancers Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body. These contrast with benign tumor A benign tumor is a mass of cells Cell most often refers to: * Cell (biolog ...
, although they involve genetic mutations to a small proportion of cells in the body, are acquired diseases. Some
cancer syndromes A cancer syndrome, or family cancer syndrome, is a genetic disorder in which inherited genetic mutation Image:Darwin Hybrid Tulip Mutation 2014-05-01.jpg, A tulip flower exhibiting a partially yellow petal due to a mutation in its genes In biol ...
, however, such as ''BRCA'' mutations, are hereditary genetic disorders.


Single-gene

A single-gene disorder (or monogenic disorder) is the result of a single mutated gene. Single-gene disorders can be passed on to subsequent generations in several ways.
Genomic imprinting #REDIRECT Genomic imprinting#REDIRECT Genomic imprinting Genomic imprinting is an epigenetic phenomenon that causes gene In biology, a gene (from ''genos'' "...Wilhelm Johannsen coined the word gene to describe the Mendelian_inheritance#His ...

Genomic imprinting
and
uniparental disomy Uniparental disomy (UPD) occurs when a person receives two copies of a chromosome A chromosome is a long DNA molecule with part or all of the genetic material of an organism. Most eukaryotic chromosomes include packaging proteins called h ...
, however, may affect inheritance patterns. The divisions between recessive and dominant types are not "hard and fast", although the divisions between
autosomal An autosome is any chromosome that is not a sex chromosome (an allosome). The members of an autosome pair in a diploid Ploidy () is the number of complete sets of chromosome A chromosome is a long DNA molecule with part or all of the ...
and
X-linked Sex linked describes the sex-specific patterns of Heredity, inheritance and Phenotype, presentation when a gene mutation (allele) is present on a sex chromosome (allosome) rather than a non-sex chromosome (autosome). In humans, these are termed ...
types are (since the latter types are distinguished purely based on the chromosomal location of the gene). For example, the common form of
dwarfism Dwarfism occurs when an organism is exceptionally small. In humans, it is sometimes defined as Short stature, an adult height of less than , regardless of sex; the average adult height among people with dwarfism is , although some individuals ...
,
achondroplasia Achondroplasia is a genetic disorder A genetic disorder is a health problem caused by one or more abnormalities in the genome In the fields of molecular biology and genetics, a genome is all genetic information of an organism. It ...
, is typically considered a dominant disorder, but children with two genes for achondroplasia have a severe and usually lethal skeletal disorder, one that achondroplasics could be considered carriers for.
Sickle-cell anemia Sickle cell disease (SCD) is a group of blood disorders typically inherited from a person's parents. The most common type is known as sickle cell anaemia (SCA). It results in an abnormality in the oxygen-carrying protein haemoglobin found in r ...
is also considered a recessive condition, but
heterozygous Zygosity (the noun, zygote, is from the Greek zygotos "yoked," from zygon "yoke") () is the degree to which both copies of a chromosome or gene have the same genetic sequence. In other words, it is the degree of similarity of the alleles in an or ...

heterozygous
carriers have increased resistance to
malaria Malaria is a mosquito-borne infectious disease that affects humans and other animals. Malaria causes symptoms Signs and symptoms are the observed or detectable signs, and experienced symptoms of an illness, injury, or condition. A sign fo ...

malaria
in early childhood, which could be described as a related dominant condition. When a couple where one partner or both are sufferers or carriers of a single-gene disorder wish to have a child, they can do so through ''in vitro'' fertilization, which enables preimplantation genetic diagnosis to occur to check whether the embryo has the genetic disorder. Most congenital
metabolic Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life Life is a characteristic that distinguishes physical entities that have biological processes, such as Cell signaling, signaling and self-sustaining ...

metabolic
disorders known as
inborn errors of metabolismInborn errors of metabolism form a large class of genetic diseases involving congenital disorders of enzyme activities. The majority are due to defects of single genes that code for enzymes that facilitate conversion of various substances (substrate ...

inborn errors of metabolism
result from single-gene defects. Many such single-gene defects can decrease the fitness of affected people and are therefore present in the population in lower frequencies compared to what would be expected based on simple probabilistic calculations.


Autosomal dominant

Only one mutated copy of the gene will be necessary for a person to be affected by an autosomal dominant disorder. Each affected person usually has one affected parent. The chance a child will inherit the mutated gene is 50%. Autosomal dominant conditions sometimes have reduced
penetrancePenetrance in genetics Genetics is a branch of biology concerned with the study of genes, genetic variation, and heredity in organisms.Hartl D, Jones E (2005) Though heredity had been observed for millennia, Gregor Mendel, Moravia, Moravian sc ...
, which means although only one mutated copy is needed, not all individuals who inherit that mutation go on to develop the disease. Examples of this type of disorder are
Huntington's disease Huntington's disease (HD), also known as Huntington's chorea, is a neurodegenerative disease that is mostly Genetic disorder#Autosomal dominant, inherited. The earliest symptoms are often subtle problems with mood or mental abilities. A gener ...
,
neurofibromatosis type 1 Neurofibromatosis type I (NF-1) is a complex multi-system human disorder caused by the mutation of a gene In biology, a gene (from ''genos'' "...Wilhelm Johannsen coined the word gene to describe the Mendelian_inheritance#History, Mendeli ...
,
neurofibromatosis type 2 Neurofibromatosis type II (also known as MISME syndrome – multiple inherited schwannomas, meningiomas, and ependymomas) is a genetic condition which may be inherited or may arise spontaneously. The main manifestation of the condition is the dev ...
,
Marfan syndrome Marfan syndrome (MFS) is a rare multi-systemic genetic disorder A genetic disorder is a health problem caused by one or more abnormalities in the genome In the fields of molecular biology and genetics Genetics is a branch of b ...
,
hereditary nonpolyposis colorectal cancer Hereditary nonpolyposis colorectal cancer (HNPCC) or Lynch syndrome is an autosomal dominant In genetics, dominance is the phenomenon of one variant (allele) of a gene on a chromosome masking or overriding the Phenotype, effect of a differen ...
,
hereditary multiple exostoses Hereditary multiple osteochondromas (HMO), also known as hereditary multiple exostoses, is a disorder characterized by the development of multiple benign osteocartilaginous masses ( exostoses) in relation to the ends of long bones of the lower lim ...
(a highly penetrant autosomal dominant disorder),
tuberous sclerosis Tuberous sclerosis complex (TSC) is a rare multisystem autosomal dominant genetic disorder, genetic disease that causes benign tumor, non-cancerous tumours to grow in the human brain, brain and on other vital organs such as the kidneys, human h ...

tuberous sclerosis
,
Von Willebrand disease Von Willebrand disease (VWD) is the most common hereditary Heredity, also called inheritance or biological inheritance, is the passing on of Phenotypic trait, traits from parents to their offspring; either through asexual reproduction or sex ...
, and
acute intermittent porphyria Acute intermittent porphyria (AIP) is a rare metabolic disorder A metabolic disorder is a disorder that negatively alters the body's processing and distribution of macronutrients such as proteins, fats, and carbohydrates. Metabolic disorders ca ...
. Birth defects are also called congenital anomalies.


Autosomal recessive

Two copies of the gene must be mutated for a person to be affected by an autosomal recessive disorder. An affected person usually has unaffected parents who each carry a single copy of the mutated gene and are referred to as
genetic carrier A hereditary carrier (genetic carrier or just carrier), is a person or other organism that has inherited a recessive allele for a genetic trait or mutation but usually does not display that trait or show symptoms of the disease A disease ...
s. Each parent with a defective gene normally do not have symptoms. Two unaffected people who each carry one copy of the mutated gene have a 25% risk with each pregnancy of having a child affected by the disorder. Examples of this type of disorder are
albinism Albinism is the congenital absence of any pigmentation or colouration in a person, animal or plant, resulting in white hair, feathers, scales and skin and pink eyes in mammals, birds, reptiles, amphibians and fish and invertebrates as well. V ...
, medium-chain acyl-CoA dehydrogenase deficiency,
cystic fibrosis Cystic fibrosis (CF) is a genetic disorder A genetic disorder is a health problem caused by one or more abnormalities in the genome. It can be caused by a mutation in a single gene In biology, a gene (from ''genos'' "...Wilhelm Johan ...
,
sickle cell disease Sickle cell disease (SCD) is a group of blood disorders typically inherited from a person's parents. The most common type is known as sickle cell anaemia (SCA). It results in an abnormality in the oxygen-carrying protein haemoglobin found in ...
,
Tay–Sachs disease Tay–Sachs disease is a genetic disorder A genetic disorder is a health problem caused by one or more abnormalities in the genome. It can be caused by a mutation in a single gene In biology, a gene (from ''genos'' "...Wilhelm Johannse ...
,
Niemann–Pick disease Niemann–Pick disease is a group of severe inherited metabolic disorders A metabolic disorder is a disorder that negatively alters the body's processing and distribution of macronutrients A nutrient is a substance Substance may refer to: * Subs ...

Niemann–Pick disease
,
spinal muscular atrophy Spinal muscular atrophy (SMA) is a rare neuromuscular disorder that results in the loss of motor neurons and progressive muscle wasting. It is usually diagnosed in infancy or early childhood and if left untreated it is the most common genetic ...
, and
Roberts syndrome Roberts syndrome, or sometimes called pseudothalidomide syndrome, is an extremely rare autosomal recessive genetic disorder that is characterized by mild to severe prenatal retardation or disruption of cell division, leading to malformation of th ...

Roberts syndrome
. Certain other phenotypes, such as wet versus dry
earwax Earwax, also known by the medical term cerumen, is a brown, orange, red, yellowish or gray wax Waxes are a diverse class of organic compound In , organic compounds are generally any s that contain - . Due to carbon's ability to (form ...
, are also determined in an autosomal recessive fashion. Some autosomal recessive disorders are common because, in the past, carrying one of the faulty genes led to a slight protection against an infectious disease or
toxin A toxin is a harmful substance produced within living cells or organisms; synthetic toxicants created by artificial processes are thus excluded. The term was first used by organic chemist Ludwig Brieger (1849–1919), derived from the word toxic ...
such as
tuberculosis Tuberculosis (TB) is an infectious disease An infection is the invasion of an organism's body Tissue (biology), tissues by Pathogen, disease-causing agents, their multiplication, and the reaction of host (biology), host tissues to the in ...

tuberculosis
or
malaria Malaria is a mosquito-borne infectious disease that affects humans and other animals. Malaria causes symptoms Signs and symptoms are the observed or detectable signs, and experienced symptoms of an illness, injury, or condition. A sign fo ...

malaria
. Such disorders include
cystic fibrosis Cystic fibrosis (CF) is a genetic disorder A genetic disorder is a health problem caused by one or more abnormalities in the genome. It can be caused by a mutation in a single gene In biology, a gene (from ''genos'' "...Wilhelm Johan ...
,
sickle cell disease Sickle cell disease (SCD) is a group of blood disorders typically inherited from a person's parents. The most common type is known as sickle cell anaemia (SCA). It results in an abnormality in the oxygen-carrying protein haemoglobin found in ...
,
phenylketonuria Phenylketonuria (PKU) is an that results in decreased of the . Untreated, PKU can lead to , s, behavioral problems, and s. It may also result in a musty smell and lighter skin. A baby born to a mother who has poorly treated PKU may have hear ...
and
thalassaemia Thalassemias are inherited blood disorders characterized by decreased hemoglobin Hemoglobin, or haemoglobin ( spelling differences) (Greek αἷμα (haîma, “blood”) + -in) + -o- + globulin (from Latin globus (“ball, sphere”) + -in) () ...
.


X-linked dominant

X-linked dominant disorders are caused by mutations in genes on the
X chromosome The X chromosome is one of the two sex-determining chromosome A chromosome is a long DNA Deoxyribonucleic acid (; DNA) is a molecule File:Pentacene on Ni(111) STM.jpg, A scanning tunneling microscopy image of pentacene molecul ...

X chromosome
. Only a few disorders have this inheritance pattern, with a prime example being X-linked hypophosphatemic rickets. Males and females are both affected in these disorders, with males typically being more severely affected than females. Some X-linked dominant conditions, such as Rett syndrome,
incontinentia pigmenti Incontinentia pigmenti (IP) is a rare X-linked dominant X-linked dominant inheritance, sometimes referred to as X-linked dominance, is a mode of Genetics, genetic Heredity, inheritance by which a dominant gene is carried on the X chromosome. A ...
type 2, and
Aicardi syndrome Aicardi syndrome is a rare genetic malformation syndrome characterized by the partial or complete absence of a key structure in the brain called the corpus callosum The corpus callosum (Latin Latin (, or , ) is a classical language belong ...
, are usually fatal in males either ''in utero'' or shortly after birth, and are therefore predominantly seen in females. Exceptions to this finding are extremely rare cases in which boys with
Klinefelter syndrome Klinefelter syndrome (KS), also known as 47,XXY is a syndrome where a male has an additional copy of the X chromosome. The primary features are infertility and small poorly functioning testicles. Often, symptoms are subtle and subjects do not ...
(44+xxy) also inherit an X-linked dominant condition and exhibit symptoms more similar to those of a female in terms of disease severity. The chance of passing on an X-linked dominant disorder differs between men and women. The sons of a man with an X-linked dominant disorder will all be unaffected (since they receive their father's Y chromosome), but his daughters will all inherit the condition. A woman with an X-linked dominant disorder has a 50% chance of having an affected fetus with each pregnancy, although in cases such as incontinentia pigmenti, only female offspring are generally viable.


X-linked recessive

X-linked recessive conditions are also caused by mutations in genes on the X chromosome. Males are much more frequently affected than females, because they only have the one X chromosome necessary for the condition to present. The chance of passing on the disorder differs between men and women. The sons of a man with an X-linked recessive disorder will not be affected (since they receive their father's Y chromosome), but his daughters will be carriers of one copy of the mutated gene. A woman who is a carrier of an X-linked recessive disorder (XRXr) has a 50% chance of having sons who are affected and a 50% chance of having daughters who are carriers of one copy of the mutated gene. X-linked recessive conditions include the serious diseases
hemophilia A Haemophilia A (or hemophilia A) is a genetic deficiency in clotting factor VIII, which causes increased bleeding and usually affects males. In the majority of cases it is inherited as an X-linked recessive trait, though there are cases which aris ...
,
Duchenne muscular dystrophy Duchenne muscular dystrophy (DMD) is a severe type of muscular dystrophy that primarily affects boys. Muscle weakness usually begins around the age of four, and worsens quickly. Muscle loss typically occurs first in the thighs and pelvis Th ...
, and
Lesch–Nyhan syndrome Lesch–Nyhan syndrome (LNS) is a rare inherited disorder caused by a deficiency of the enzyme Enzymes () are proteins that act as biological catalysts (biocatalysts). Catalysts accelerate chemical reactions. The molecules upon which enzy ...
, as well as common and less serious conditions such as
male pattern baldness Pattern hair loss is hair loss Hair loss, also known as alopecia or baldness, refers to a loss of hair Hair is a protein filament In biology Biology is the natural science that studies life and living organisms, including th ...

male pattern baldness
and red–green
color blindness Color blindness (color vision deficiency) is the decreased ability to see color or differences in color Color (American English American English (AmE, AE, AmEng, USEng, en-US), sometimes called United States English or U.S. Eng ...

color blindness
. X-linked recessive conditions can sometimes manifest in females due to
skewed X-inactivation Skewed X-chromosome inactivation (skewed X-inactivation) occurs when the X-inactivation of one X chromosome The X chromosome is one of the two sex-determining chromosome A chromosome is a long DNA molecule with part or all of the genetic ...
or monosomy X (
Turner syndrome Turner syndrome (TS), also known 45,X, or 45,X0, is a genetic condition in which a female is partly or completely missing an X chromosome. Signs and symptoms vary among those affected. Often, a short and webbed neck, low-set ears, low hairline at ...
).


Y-linked

Y-linked disorders are caused by mutations on the Y chromosome. These conditions may only be transmitted from the heterogametic sex (e.g. male humans) to offspring of the same sex. More simply, this means that Y-linked disorders in humans can only be passed from men to their sons; females can never be affected because they do not possess Y-allosomes. Y-linked disorders are exceedingly rare but the most well-known examples typically cause infertility. Reproduction in such conditions is only possible through the circumvention of infertility by medical intervention.


Mitochondrial

This type of inheritance, also known as maternal inheritance, is the rarest and applies to the 13 genes encoded by
mitochondrial DNA Mitochondrial DNA (mtDNA or mDNA) is the DNA Deoxyribonucleic acid (; DNA) is a molecule File:Pentacene on Ni(111) STM.jpg, A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of five car ...

mitochondrial DNA
. Because only egg cells contribute mitochondria to the developing embryo, only mothers (who are affected) can pass on mitochondrial DNA conditions to their children. An example of this type of disorder is
Leber's hereditary optic neuropathy Leber's hereditary optic neuropathy (LHON) is a mitochondrially inherited (transmitted from mother to offspring) degeneration of retinal ganglion cells (RGCs) and their axon An axon (from Greek ἄξων ''áxōn'', axis), or nerve fiber (o ...
. It is important to stress that the vast majority of
mitochondrial diseases Mitochondrial disease is a group of disorders caused by mitochondrial dysfunction. Mitochondria A mitochondrion (; ) is a double-membrane Image:Schematic size.jpg, up150px, Schematic of size-based membrane exclusion A membrane is a selecti ...
(particularly when symptoms develop in early life) are actually caused by a
nuclear geneA nuclear gene is a gene In biology, a gene (from ''genos'' "...Wilhelm Johannsen coined the word gene to describe the Mendelian_inheritance#History, Mendelian units of heredity..." (Greek language, Greek) meaning ''generation'' or ''birth'' ...
defect, as the mitochondria are mostly developed by non-mitochondrial DNA. These diseases most often follow autosomal recessive inheritance.


Multifactorial disorder

Genetic disorders may also be complex, multifactorial, or polygenic, meaning they are likely associated with the effects of multiple genes in combination with lifestyles and environmental factors. Multifactorial disorders include
heart disease Cardiovascular disease (CVD) is a class of diseases that involve the heart or blood vessels. CVD includes coronary artery diseases (CAD) such as angina pectoris, angina and myocardial infarction (commonly known as a heart attack). Other CVDs inc ...
and
diabetes Diabetes mellitus, commonly known as just diabetes, is a group of metabolic disorder A metabolic disorder is a disorder that negatively alters the body's processing and distribution of macronutrients such as proteins, fats, and carbohydrate ...

diabetes
. Although complex disorders often cluster in families, they do not have a clear-cut pattern of inheritance. This makes it difficult to determine a person's risk of inheriting or passing on these disorders. Complex disorders are also difficult to study and treat because the specific factors that cause most of these disorders have not yet been identified. Studies that aim to identify the cause of complex disorders can use several methodological approaches to determine
genotype The genotype of an organism is its complete set of genetic material. Genotype can also be used to refer to the or variants an individual carries in a particular gene or genetic location. The number of alleles an individual can have in a specific ...
phenotype In genetics Genetics is a branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular inter ...

phenotype
associations. One method, the genotype-first approach, starts by identifying genetic variants within patients and then determining the associated clinical manifestations. This is opposed to the more traditional phenotype-first approach, and may identify causal factors that have previously been obscured by clinical
heterogeneity Homogeneity and heterogeneity are concepts often used in the sciences Science (from the Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally ...
,
penetrancePenetrance in genetics Genetics is a branch of biology concerned with the study of genes, genetic variation, and heredity in organisms.Hartl D, Jones E (2005) Though heredity had been observed for millennia, Gregor Mendel, Moravia, Moravian sc ...
, and expressivity. On a pedigree, polygenic diseases do tend to "run in families", but the inheritance does not fit simple patterns as with
Mendelian Mendelian inheritance is a type of biological inheritance Inheritance is the practice of passing on private property, titles A title is one or more words used before or after a person's name, in certain contexts. It may signify either ...
diseases. This does not mean that the genes cannot eventually be located and studied. There is also a strong environmental component to many of them (e.g.,
blood pressure Blood pressure (BP) is the pressure Pressure (symbol: ''p'' or ''P'') is the force In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motio ...

blood pressure
). Other factors include: *
asthma Asthma is a long-term Long-Term Capital Management L.P. (LTCM) was a hedge fund''A financial History of the United States Volume II: 1970–2001'', Jerry W. Markham, Chapter 5: "Bank Consolidation", M. E. Sharpe, Inc., 2002 based in Greenwich, ...

asthma
*
autoimmune diseases An autoimmune disease is a condition arising from an abnormal immune response to a functioning body part. There are at least 80 types of autoimmune diseases. Nearly any body part can be involved. Common symptoms include low grade fever and fatigu ...
such as
multiple sclerosis Multiple sclerosis (MS), also known as encephalomyelitis disseminata, is the most common demyelinating disease, in which the Myelin, insulating covers of nerve cells in the Human brain, brain and spinal cord are damaged. This damage disrupts the ...
*
cancers Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body. These contrast with benign tumor A benign tumor is a mass of cells Cell most often refers to: * Cell (biolog ...
* ciliopathies *
cleft palate A cleft lip contains an opening in the upper lip Lips are a visible body part at the mouth of many animals, including humans. Lips are soft, movable, and serve as the opening for food intake and in the articulation of sound and speech. Hu ...

cleft palate
*
diabetes Diabetes mellitus, commonly known as just diabetes, is a group of metabolic disorder A metabolic disorder is a disorder that negatively alters the body's processing and distribution of macronutrients such as proteins, fats, and carbohydrate ...

diabetes
*
heart disease Cardiovascular disease (CVD) is a class of diseases that involve the heart or blood vessels. CVD includes coronary artery diseases (CAD) such as angina pectoris, angina and myocardial infarction (commonly known as a heart attack). Other CVDs inc ...
*
hypertension Hypertension (HTN or HT), also known as high blood pressure (HBP), is a Chronic condition, long-term Disease, medical condition in which the blood pressure in the artery, arteries is persistently elevated. High blood pressure usually does not ...

hypertension
*
inflammatory bowel disease Inflammatory bowel disease (IBD) is a group of inflammation, inflammatory conditions of the colon (anatomy), colon and small intestine, Crohn's disease and ulcerative colitis being the principal types. Crohn's disease affects the small intestine an ...
*
intellectual disability Intellectual disability (ID), also known as general learning disability and formerly mental retardation (MR),Rosa's Law, Pub. L. 111-256124 Stat. 2643(2010). is a generalized neurodevelopmental disorder characterized by significantly impaired in ...
*
mood disorder Mood disorder, also known as mood affective disorders, is a group of conditions where a disturbance in the person's mood is the main underlying feature. The classification is in the ''Diagnostic and Statistical Manual of Mental Disorders The ...
*
obesity Obesity is a medical condition A disease is a particular abnormal condition that negatively affects the structure or function (biology), function of all or part of an organism, and that is not due to any immediate external injury. ...

obesity
*
refractive error Refractive error, also known as refraction error, is a problem with focus FOCUS is a fourth-generation programming language (4GL) computer programming programming language, language and development environment that is used to build database quer ...

refractive error
*
infertility Infertility is the inability of a person, animal or plant to Sexual reproduction, reproduce by natural means. It is usually not the natural state of a healthy adult, except notably among certain eusocial species (mostly haplodiploid insects). I ...


Chromosomal disorder

A chromosomal disorder is a missing, extra, or irregular portion of chromosomal DNA. It can be from an atypical number of chromosomes or a structural abnormality in one or more chromosomes. An example of these disorders is trisomy 21 (
Down syndrome Down syndrome or Down's syndrome, also known as trisomy 21, is a genetic disorder A genetic disorder is a health problem caused by one or more abnormalities in the genome In the fields of molecular biology and genetics Gen ...
), in which there is an extra copy of chromosome 21.


Diagnosis

Due to the wide range of genetic disorders that are known, diagnosis is widely varied and dependent of the disorder. Most genetic disorders are diagnosed pre-birth, at birth, or during early childhood however some, such as
Huntington's disease Huntington's disease (HD), also known as Huntington's chorea, is a neurodegenerative disease that is mostly Genetic disorder#Autosomal dominant, inherited. The earliest symptoms are often subtle problems with mood or mental abilities. A gener ...
, can escape detection until the patient is well into adulthood. The basic aspects of a genetic disorder rests on the inheritance of genetic material. With an in depth
family history Genealogy (from el, γενεαλογία ' "study of family trees") is the study of families In human society, family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinit ...
, it is possible to anticipate possible disorders in children which direct medical professionals to specific tests depending on the disorder and allow parents the chance to prepare for potential lifestyle changes, anticipate the possibility of
stillbirth Stillbirth is typically defined as fetal A fetus or foetus (; plural fetuses, feti, foetuses, or foeti) is the unborn offspring of an animal that develops from an embryo An embryo is the early stage of development of a multicellular or ...
, or contemplate
termination Termination may refer to: Science *Termination (geomorphology), the period of time of relatively rapid change from cold, glacial conditions to warm interglacial condition *Termination factor, in genetics, part of the process of transcribing RNA ...
.
Prenatal diagnosis Prenatal development () includes the development of the embryo and of the foetus during a viviparous animal's gestationGestation is the period of development during the carrying of an embryo An embryo is the early stage of development of a ...
can detect the presence of characteristic abnormalities in fetal development through
ultrasound Ultrasound is sound wave In physics Physics is the that studies , its , its and behavior through , and the related entities of and . "Physical science is that department of knowledge which relates to the order of nature, or, ...
, or detect the presence of characteristic substances via invasive procedures which involve inserting probes or needles into the uterus such as in
amniocentesis Amniocentesis (also referred to as an amniotic fluid test or, informally, an "amnio") is a medical procedureThe word ''amniocentesis'' itself indicates precisely the procedure in question, Ancient Greek, Greek ἀμνίον ''amníon'' being the "i ...

amniocentesis
.


Prognosis

Not all genetic disorders directly result in death; however, there are no known cures for genetic disorders. Many genetic disorders affect stages of development, such as
Down syndrome Down syndrome or Down's syndrome, also known as trisomy 21, is a genetic disorder A genetic disorder is a health problem caused by one or more abnormalities in the genome In the fields of molecular biology and genetics Gen ...
, while others result in purely physical symptoms such as
muscular dystrophy Muscular dystrophies (MD) are a genetically and clinically heterogeneous group of rare neuromuscular disease A neuromuscular junction (or myoneural junction) is a chemical synapse between a motor neuron A motor neuron (or motoneuron) is a ne ...
. Other disorders, such as
Huntington's disease Huntington's disease (HD), also known as Huntington's chorea, is a neurodegenerative disease that is mostly Genetic disorder#Autosomal dominant, inherited. The earliest symptoms are often subtle problems with mood or mental abilities. A gener ...
, show no signs until adulthood. During the active time of a genetic disorder, patients mostly rely on maintaining or slowing the degradation of
quality of life Quality of life (QOL) is defined by the World Health Organization The World Health Organization (WHO) is a specialized agency of the United Nations United Nations Specialized Agencies are autonomous organizations working with the United N ...
and maintain patient
autonomy In developmental psychology Developmental psychology is the scientific Science () is a systematic enterprise that Scientific method, builds and organizes knowledge in the form of Testability, testable explanations and predictions ...

autonomy
. This includes
physical therapy Physical therapy (PT), also known as physiotherapy, is one of the allied health professions Allied health professions are health care Health care, health-care, or healthcare is the maintenance or improvement of health via the preventive h ...

physical therapy
,
pain management Pain management, pain killer, pain medicine, pain control or algiatry, is a branch of medicine Medicine is the science Science () is a systematic enterprise that builds and organizes knowledge Knowledge is a familiarity, awarenes ...
, and may include a selection of
alternative medicine Alternative medicine is any practice that aims to achieve the healing effects of medicine, but which lacks biological plausibility and is Argument from ignorance, untested, Pseudoscience, untestable or proven ineffective. Complementary medicin ...
programs.


Treatment

The treatment of genetic disorders is an ongoing battle, with over 1,800
gene therapy Gene therapy is a medical Medicine is the science Science () is a systematic enterprise that builds and organizes knowledge Knowledge is a familiarity, awareness, or understanding of someone or something, such as facts ( descri ...

gene therapy
clinical trials having been completed, are ongoing, or have been approved worldwide. Despite this, most treatment options revolve around treating the symptoms of the disorders in an attempt to improve patient
quality of life Quality of life (QOL) is defined by the World Health Organization The World Health Organization (WHO) is a specialized agency of the United Nations United Nations Specialized Agencies are autonomous organizations working with the United N ...
. Gene therapy refers to a form of treatment where a healthy gene is introduced to a patient. This should alleviate the defect caused by a faulty gene or slow the progression of the disease. A major obstacle has been the delivery of genes to the appropriate cell, tissue, and organ affected by the disorder. Researchers have investigated how they can introduce a gene into the potentially trillions of cells that carry the defective copy. Finding an answer to this has been a roadblock between understanding the genetic disorder and correcting the genetic disorder.


Epidemiology

Around 1 in 50 people are affected by a known single-gene disorder, while around 1 in 263 are affected by a
chromosomal disorder A chromosome abnormality, chromosomal anomaly, chromosomal aberration, chromosomal mutation, or chromosomal disorder, is a missing, extra, or irregular portion of chromosomal DNA. These can occur in the form of numerical abnormalities, where there i ...
. Around 65% of people have some kind of health problem as a result of congenital genetic mutations. Due to the significantly large number of genetic disorders, approximately 1 in 21 people are affected by a genetic disorder classified as "
rare Rare may refer to: * Rare, a particular Doneness, temperature of meat * Something infrequent or scarce, see Scarcity :* Rare species, a conservation category in biology designating the scarcity of an organism and implying a threat to its viability ...
" (usually defined as affecting less than 1 in 2,000 people). Most genetic disorders are rare in themselves. There are well over 6,000 known genetic disorders, and new genetic disorders are constantly being described in medical literature.


History

The earliest known genetic condition in a
hominid The Hominidae (), whose members are known as great apes or hominids (), are a taxonomic family In , family (from la, familia) is a of people related either by (by recognized birth) or (by marriage or other relationship). The purpose ...
was in the fossil species ''
Paranthropus robustus ''Paranthropus robustus'' is a species of robustness (morphology), robust australopithecine from the Early Pleistocene, Early and possibly Middle Pleistocene, Middle Pleistocene of the Cradle of Humankind, South Africa, about 2.27 to 0.87 (or, mo ...
,'' with over a third of individuals displaying
amelogenesis imperfecta Amelogenesis imperfecta (AI) is a congenital disorder which presents with a rare abnormal formation of the enamel or external layer of the crown of teeth A tooth (plural teeth) is a hard, calcified Calcification is the accumulation of calc ...
.


See also

* FINDbase (the Frequency of Inherited Disorders database) *
Genetic epidemiology Genetic epidemiology is the study of the role of genetics, genetic factors in determining health and disease in families and in populations, and the interplay of such genetic factors with environmental factors. Genetic epidemiology seeks to derive a ...
*
List of genetic disorders The following is a list of genetic disorders and if known, type of mutation and for the chromosome involved. Although the parlance "disease-causing gene" is common, it is the occurrence of an mutation, abnormality in the parents that causes the di ...
* Population groups in biomedicine *
Mendelian error A Mendelian error in the genetic analysis of a species, describes an allele in an individual which could not have been received from either of its biological parents by Mendelian inheritance. Inheritance is defined by a set of related individuals ...


References


External links


Public Health Genomics at CDC

OMIM — Online Mendelian Inheritance in Man, a catalog of human genes and genetic disorders

Genetic and Rare Diseases Information Center (GARD)
Office of Rare Diseases (ORD), National Institutes of Health (NIH)

* ttps://web.archive.org/web/20080905105100/http://www.ornl.gov/hgmis/medicine/assist.html Genetic Disease Information from the Human Genome Project
Global Genes Project, Genetic and Rare Diseases Organization

List of Genetic Disorders - Genome.gov
{{DEFAULTSORT:Genetic Disorder