Blaschko's lines, also called the lines of Blaschko, are lines of normal cell development in the
skin
Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main functions: protection, regulation, and sensation.
Other cuticle, animal coverings, such as the arthropod exoskeleton, have diffe ...
. These lines are only visible in those with a
mosaic
A mosaic is a pattern or image made of small regular or irregular pieces of colored stone, glass or ceramic, held in place by plaster/mortar, and covering a surface. Mosaics are often used as floor and wall decoration, and were particularly pop ...
skin condition or in
chimeras where different cell lines contain different genes. These lines may express different amounts of
melanin
Melanin (; from el, μέλας, melas, black, dark) is a broad term for a group of natural pigments found in most organisms. Eumelanin is produced through a multistage chemical process known as melanogenesis, where the oxidation of the amino ...
,
or become visible due to a differing susceptibility to disease. In such individuals, they can become apparent as whorls, patches, streaks or lines in a linear or segmental distribution over the skin. They follow a ''V'' shape over the back, ''S''-shaped whirls over the chest and sides, and wavy shapes on the head. Not all mosaic skin conditions follow Blascko's lines.
The lines are believed to trace the migration of
embryonic cell
In biology, a blastomere is a type of Cell (biology), cell produced by cleavage (embryo), cell division (cleavage) of the zygote after fertilization; blastomeres are an essential part of blastula formation, and blastocyst formation in mammals.
Hum ...
s. They do not correspond to
nervous,
muscular
Skeletal muscles (commonly referred to as muscles) are 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 types of muscle ...
, or
lymphatic
Lymph (from Latin, , meaning "water") is the fluid that flows through the lymphatic system, a system composed of lymph vessels (channels) and intervening lymph nodes whose function, like the venous system, is to return fluid from the tissues to ...
systems. The lines are not unique to humans and can be observed in other non-human animals with mosaicism.
Alfred Blaschko is credited with the first demonstration of these lines in 1901.
Signs and symptoms
The skin lesions that follow Blaschko's lines are varied. They include
genetic,
congenital
A birth defect, also known as a congenital disorder, is an abnormal condition that is present at birth regardless of its cause. Birth defects may result in disabilities that may be physical, intellectual, or developmental. The disabilities can ...
and acquired (i.e., non-genetic) conditions. Examples include:
* Pigmentary disorders
** Nevus achromicus (including
incontinentia pigmenti achromians, also known as hypomelanosis of Ito)
** Epidermal
nevus
Nevus (plural nevi) is a nonspecific medical term for a visible, circumscribed, chronic lesion of the skin or mucosa. The term originates from ''nævus'', which is Latin for "birthmark"; however, a nevus can be either congenital (present at bir ...
***
Nevus sebaceus
Nevus sebaceus or sebaceous nevus (the first term is its Latin name, the second term is its name in English; also known as an "organoid nevus"James, William; Berger, Timothy; Elston, Dirk (2005). ''Andrews' Diseases of the Skin: Clinical Dermatolog ...
***
Inflammatory linear verrucous epidermal nevus
Inflammatory Linear Verrucous Epidermal Nevus is a rare disease of the skin that presents as multiple, discrete, red papules that tend to coalesce into linear plaques that follow the Lines of Blaschko. The plaques can be slightly warty (psoriafor ...
*
X-linked
Sex linked describes the sex-specific patterns of inheritance and 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 X-linked recessive, ...
genetic skin disorder
**
Incontinentia pigmenti
Incontinentia pigmenti (IP) is a rare X-linked dominant genetic disorder that affects the skin, hair, teeth, nails and central nervous system. It is named from its appearance under a microscope.
The disease is characterized by skin abnormalitie ...
**
CHILD syndrome
Congenital hemidysplasia with ichthyosiform erythroderma and limb defects (also known as "CHILD syndrome") is a genetic disorder with onset at birth seen almost exclusively in females.Freedberg, et al. (2003). ''Fitzpatrick's Dermatology in Gener ...
**
X-linked reticulate pigmentary disorder
X-linked reticulate pigmentary disorder is a rare X-linked genetic condition in which males manifest multiple systemic symptoms and a reticulated mottled brown pigmentation of the skin, which, on biopsy, demonstrated dermal deposits of amyloid. F ...
* Acquired inflammatory skin rashes
**
Lichen striatus
Lichen striatus is a rare skin condition that is seen primarily in children, most frequently appearing ages 5–15. It consists of a self-limiting eruption of small, scaly papules.
Symptoms
Lichen striatus impacts the skin and nails. It is se ...
**
Lichen planus
Lichen planus (LP) is a chronic inflammatory and immune-mediated disease that affects the skin, nails, hair, and mucous membranes. It is not an actual lichen, and is only named that because it looks like one. It is characterized by polygonal, fla ...
**
Lupus erythematosus
Lupus erythematosus is a collection of autoimmune diseases in which the human immune system becomes hyperactive and attacks healthy tissues. Symptoms of these diseases can affect many different body systems, including joints, skin, kidneys, blo ...
*
Chimerism
A genetic chimerism or chimera ( ) is a single organism composed of cells with more than one distinct genotype. In animals, this means an individual derived from two or more zygotes, which can include possessing blood cells of different blood ...
*
McCune-Albright syndrome
History
Alfred Blaschko, a private practice dermatologist from Berlin, first described and drew the patterns of the lines of Blaschko in 1901. He obtained his data by studying over 140 patients with various
nevoid and acquired skin diseases and transposed the visible patterns the diseases followed onto dolls and statues, then compiled the patterns onto a composite schematic of the human body. He described a system of lines across the surface of the human body that nevi and dermatological diseases tended to follow, unrelated to the dermatomes of the body or any other cutaneous or subcutaneous structure.
In the same month of 1901, an American dermatologist named Douglas Montgomery presented his own research paper before the American Dermatological Society, based on his studies of extensive linear nevi in human patients. Similar to Blaschko, he suggested that the linear patterns of nevi followed "streams" of tissue growth that occurred during embryogenesis rather than being related to an epidermal structure.
In 1945, the
Journal of Heredity
The ''Journal of Heredity'' is a peer-reviewed scientific journal concerned with heredity in a biological sense, covering all aspects of genetics. It is published by Oxford University Press on behalf of the American Genetic Association.
Histor ...
published Russian scientist Moisey Davidovich Zlotnikov's research describing a 24-year-old woman with a unilateral, systematized nevus across the left side of her body, and proposed that the disorder was due to a mutation during the cell cleavage stage of development. Based on this hypothesis, Zlotnikov suggested that the only probable explanation for the sagittal asymmetry of the disease was a
genetic mosaicism in the patient.
However, this proposal was not widely explored until re-hypothesized by German dermatologist Rudolf Happle in the 1970s due to the state of genetic and medical research in the Soviet Union at the time, and recent end of World War II.
The lines of Blaschko were first referred to as such by the English-speaking medical community after 1976, when Robert Jackson published a review and reconsideration of Blaschko's research. Jackson wished to inspire interaction between dermatologists who saw Blaschko's lines in patients, and developmental biologists studying embryology and chromosomal abnormalities such as mosaicism.
Scientists such as Rudolf Happle and Jean Bolognia have further differentiated Blaschko's lines from other linear phenomena such as
Langer's lines
Langer's lines, Langer lines of skin tension, or sometimes called cleavage lines, are topological lines drawn on a map of the human body. They are parallel to the natural orientation of collagen fibers in the dermis, and generally perpendicular to ...
and expanded the map of the lines over the human body to include areas of the head, face, and neck, where Blaschko's original maps did not cover.
In 1985, Rudolf Happle proposed a link to
lyonization
X-inactivation (also called Lyonization, after English geneticist Mary Lyon) is a process by which one of the copies of the X chromosome is inactivated in therian female mammals. The inactive X chromosome is silenced by being packaged into a ...
and investigated the link to other X-linked skin disorders. Since that year, Scientists have continually explored the developmental hypothesis for the origins of Blaschko's lines, having found biological evidence to support the theory and linking the lines to other mosaicism and genetic-development related conditions and phenomena of the skin.
See also
* Head zones (
dermatomes)
*
Kraissl's lines Kraissl's lines are a set of anatomical skin lines. They differ from Langer's lines in that unlike Langer's lines, which are defined in term of collagen orientation, Kraissl's lines are the lines of maximum skin tension.
Whereas Langer's lines w ...
*
Langer's lines
Langer's lines, Langer lines of skin tension, or sometimes called cleavage lines, are topological lines drawn on a map of the human body. They are parallel to the natural orientation of collagen fibers in the dermis, and generally perpendicular to ...
*
List of cutaneous conditions
Many skin conditions affect the human integumentary system—the organ system covering the entire surface of the body and composed of skin, hair, nails, and related muscle and glands. The major function of this system is as a barrier against t ...
References
External links
* {{cite web, title=Blaschko's lines, url=http://www.pcds.org.uk/clinical-guidance/blaschkos-lines, website=www.pcds.org.uk
Description of Blaschko's linesUnderstanding Genetics - ask a geneticist
Skin anatomy
Skin lines