Congenital generalized lipodystrophy (also known as Berardinelli–Seip lipodystrophy) is an extremely rare autosomal recessive condition, characterized by an extreme scarcity of fat in the subcutaneous tissues. It is a type of lipodystophy disorder where the magnitude of fat loss determines the severity of metabolic complications. Only 250 cases of the condition have been reported, and it is estimated that it occurs in 1 in 10 million people worldwide.

Presentation

Congenital generalized lipodystrophy (CGL) is a rare autosomal recessive disorder which manifests with

insulin resistance Insulin resistance (IR) is a pathological condition in which cells fail to respond normally to the hormone insulin. Insulin is a hormone that facilitates the transport of glucose from blood into cells, thereby reducing blood glucose (blood suga ...

, absence of subcutaneous fat and muscular

hypertrophy Hypertrophy is the increase in the volume of an organ or tissue due to the enlargement of its component cells. It is distinguished from hyperplasia, in which the cells remain approximately the same size but increase in number.Updated by Linda J ...

. Homozygous or compound heterozygous mutations in four genes are associated with the four subtypes of CGL. The condition appears in early childhood with accelerated linear growth, quick aging of bones, and a large appetite. As the child grows up,

acanthosis nigricans Acanthosis nigricans is a medical sign characterised by brown-to-black, poorly defined, velvety hyperpigmentation of the skin. It is usually found in body folds, such as the posterior and lateral folds of the neck, the armpits, groin, navel, f ...

( hyperpigmentation and thickening of skin) will begin to present itself throughout the body – mainly in the neck, trunk, and groin. The disorder also has characteristic features like

hepatomegaly Hepatomegaly is the condition of having an enlarged liver. It is a non-specific medical sign having many causes, which can broadly be broken down into infection, hepatic tumours, or metabolic disorder. Often, hepatomegaly will present as an ab ...

or an enlarged liver which arises from

fatty liver Fatty liver disease (FLD), also known as hepatic steatosis, is a condition where excess fat builds up in the liver. Often there are no or few symptoms. Occasionally there may be tiredness or pain in the upper right side of the abdomen. Complic ...

and may lead to

cirrhosis Cirrhosis, also known as liver cirrhosis or hepatic cirrhosis, and end-stage liver disease, is the impaired liver function caused by the formation of scar tissue known as fibrosis due to damage caused by liver disease. Damage causes tissue repai ...

muscle Skeletal muscles (commonly referred to as muscles) are Organ (biology), organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other ...

, lack of

adipose tissue Adipose tissue, body fat, or simply fat is a loose connective tissue composed mostly of adipocytes. In addition to adipocytes, adipose tissue contains the stromal vascular fraction (SVF) of cells including preadipocytes, fibroblasts, vascular ...

splenomegaly Splenomegaly is an enlargement of the spleen. The spleen usually lies in the left upper quadrant (LUQ) of the human abdomen. Splenomegaly is one of the four cardinal signs of ''hypersplenism'' which include: some reduction in number of circulati ...

hirsutism Hirsutism is excessive body hair on parts of the body where hair is normally absent or minimal. The word is from early 17th century: from Latin ''hirsutus'' meaning "hairy". It usually refers to a "male" pattern of hair growth in a female that ...

(excessive hairiness) and

hypertriglyceridemia Hypertriglyceridemia is the presence of high amounts of triglycerides in the blood. Triglycerides are the most abundant fatty molecule in most organisms. Hypertriglyceridemia occurs in various physiologic conditions and in various diseases, and ...

. Fatty liver and muscle hypertrophy arise from the fact that lipids are instead stored in these areas; whereas in a healthy individual, lipids are distributed more uniformly throughout the body subcutaneously. The absence of adipose tissue where they normally occur causes the body to store fat in the remaining areas. Common

cardiovascular The blood circulatory system is a system of organs that includes the heart, blood vessels, and blood which is circulated throughout the entire body of a human or other vertebrate. It includes the cardiovascular system, or vascular system, tha ...

problems related to this syndrome are

cardiac hypertrophy Ventricular hypertrophy (VH) is thickening of the walls of a ventricle (lower chamber) of the heart. Although left ventricular hypertrophy (LVH) is more common, right ventricular hypertrophy (RVH), as well as concurrent hypertrophy of both ventri ...

and arterial hypertension (high

blood pressure Blood pressure (BP) is the pressure of circulating blood against the walls of blood vessels. Most of this pressure results from the heart pumping blood through the circulatory system. When used without qualification, the term "blood pressur ...

). This disorder can also cause

metabolic syndrome Metabolic syndrome is a clustering of at least three of the following five medical conditions: abdominal obesity, high blood pressure, high blood sugar, high serum triglycerides, and low serum high-density lipoprotein (HDL). Metabolic syndrom ...

. Most with the disorder also have a prominent umbilicus or umbilical hernia. Commonly, patients will also have

acromegaly Acromegaly is a disorder that results from excess growth hormone (GH) after the growth plates have closed. The initial symptom is typically enlargement of the hands and feet. There may also be an enlargement of the forehead, jaw, and nose. Othe ...

with enlargement of the hands, feet, and jaw. After puberty, additional symptoms can develop. In women,

clitoromegaly Clitoromegaly (or macroclitoris) is an abnormal enlargement of the clitoris that is mostly congenital or acquired, though deliberately induced clitoris enlargement as a form of genital body modification is achieved through various uses of anabol ...

and polycystic ovary syndrome can develop. This impairs fertility for women, and only a few documented cases of successful pregnancies in women with CGL exist. However, the fertility of men with the disorder is unaffected.

Type 1 vs Type 2 Differences

There are differences in how Type 1 vs Type 2 patients are affected by the disease. In type 1 patients, they still have mechanical adipose tissue, but type 2 patients do not have any adipose tissue, including mechanical. In type 2 patients, there is a greater likelihood of psychomotor retardation and intellectual impairment.

Genetics

Mechanism

Type 1

In individuals with Type 1 CGL, the disorder is caused by a mutation at the AGPAT2 gene encoding 1-acylglycerol-3-phosphate O-acyltransferase 2 and located at 9q34.3. This enzyme catalyzes the acylation of

lysophosphatidic acid Lysophosphatidic acid (LPA) is a phospholipid derivative that can act as a lipid signaling, signaling molecule. Function LPA acts as a potent mitogen due to its activation of three high-affinity G-protein-coupled receptors called LPAR1, LPAR2, a ...

to form

phosphatidic acid Phosphatidic acids are anionic phospholipids important to cell signaling and direct activation of lipid-gated ion channels. Hydrolysis of phosphatidic acid gives rise to one molecule each of glycerol and phosphoric acid and two molecules of fatty a ...

, which is important in the biosynthesis of fats. This enzyme is highly expressed in

, so it can be concluded that when the enzyme is defective in CGL, lipids cannot be stored in the adipose tissue.

Type 2

In those who have Type 2 CGL, a mutation in the BSCL2 gene encoding the Seipin protein and located at 11q13. This gene encodes a protein, Seipin, whose function is unknown. Expression of mRNA for the seipin protein is high in the brain, yet low in

s. Additionally, patients which have mutations in this protein have a higher incidence of

mental retardation Intellectual disability (ID), also known as general learning disability in the United Kingdom and formerly mental retardation, Rosa's Law, Pub. L. 111-256124 Stat. 2643(2010). is a generalized neurodevelopmental disorder characterized by signif ...

and lack mechanically active adipose tissue, which is present in those with AGPAT2 mutations.

Type 3

Type 3 CGL involves a mutation in the CAV1 gene. This gene codes for the

Caveolin In molecular biology, caveolins are a family of integral membrane proteins that are the principal components of caveolae membranes and involved in receptor-independent endocytosis. Caveolins may act as scaffolding proteins within caveolar memb ...

protein, which is a scaffolding membrane protein. This protein plays a role in lipid regulation. High levels of Cav1 are normally expressed in adipocytes. Thus, when the CAV1 gene mutates the adipocytes do not have Cav1 and are unable to properly regulate lipid levels.

Type 4

A mutation in the PTRF gene causes Type 4 CGL. This gene codes for a protein called polymerase I and transcript release factor. One of the roles the PTRF product has it to stabilize and aid in formation of caveolae. Thus, the mechanism is similar to Type 3, in that the caveolae are unable to properly form and carry out their role in lipid regulation in both. Types 3 and 4 are two different mutations but they share a common defective pathway.

Diagnosis

Medical diagnosis of CGL can be made after observing the physical symptoms of the disease: lipoatrophy (loss of fat tissues) affecting the trunk, limbs, and face;

;

; and high serum levels of triglycerides. Genetic testing can also confirm the disease, as mutations in the AGPAT2 gene is indicative of CGL1, a mutation in the BSCL2 gene is indicative of CGL2, and mutations in the CAV1 and PTRF genes are indicative of CGL3 and CGL4 respectively. Physical diagnosis of CGL is easier, as CGL patients are recognizable from birth, due to their extreme muscular appearance, which is caused by the absence of subcutaneous fat. CGL3 patients have

serum Serum may refer to: *Serum (blood), plasma from which the clotting proteins have been removed **Antiserum, blood serum with specific antibodies for passive immunity * Serous fluid, any clear bodily fluid * Truth serum, a drug that is likely to mak ...

creatine kinase Creatine kinase (CK), also known as creatine phosphokinase (CPK) or phosphocreatine kinase, is an enzyme () expressed by various tissues and cell types. CK catalyses the conversion of creatine and uses adenosine triphosphate (ATP) to create phos ...

concentrations much higher than normal (2.5 to 10 times the normal limit). This can be used to diagnose type 3 patients and differentiate them from CGL 1 and 2 without mapping their genes. Additionally, CGL3 patients have low muscle tone when compared with other CGL patients.

Treatment

Metformin Metformin, sold under the brand name Glucophage, among others, is the main first-line medication for the treatment of type 2 diabetes, particularly in people who are overweight. It is also used in the treatment of polycystic ovary syndrome. ...

is the main drug used for treatment, as it is normally used for patients with

hyperglycemia Hyperglycemia is a condition in which an excessive amount of glucose circulates in the blood plasma. This is generally a blood sugar level higher than 11.1 mmol/L (200 mg/dL), but symptoms may not start to become noticeable until even ...

. Metformin reduces appetite and improves symptoms of hepatic steatosis and polycystic ovary syndrome. Leptin can also be used to reverse

and hepatic steatosis, to cause reduced food intake, and decrease

blood glucose Glycaemia, also known as blood sugar level, blood sugar concentration, or blood glucose level is the measure of glucose concentrated in the blood of humans or other animals. Approximately 4 grams of glucose, a simple sugar, is present in the bl ...

levels.

Diet

CGL patients have to maintain a strict diet for life, as their excess appetite will cause them to overeat. Carbohydrate intake should be restricted in these patients. To avoid chylomicronemia, CGL patients with

need to have a diet very low in fat. CGL patients also need to avoid total

proteins Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respondi ...

, trans fats, and eat high amounts of soluble fiber to avoid getting high levels of

cholesterol Cholesterol is any of a class of certain organic molecules called lipids. It is a sterol (or modified steroid), a type of lipid. Cholesterol is biosynthesized by all animal cells and is an essential structural component of animal cell membr ...

in the blood.

History

Congenital Generalized Lipodystrophy, also known as Berardinelli–Seip lipodystrophy was first described in 1954 by Berardinelli and later by Seip in 1959. The gene for type 1 CGL was identified as AGPAT2 at chromosome 9q34, and later the gene for type 2 CGL was identified as BSCL2 at chromosome 11q13. More recently, type 3 CGL was identified as a separate type of CGL, which was identified as a mutation in the CAV1 gene. Then, a separate type 4 CGL was identified as a mutation in the PTRF gene.

References

External links

{{Deficiencies of intracellular signaling peptides and proteins Conditions of the subcutaneous fat Genetic disorders by system Rare syndromes