Ectodysplasin A receptor (EDAR) is a protein that in humans is encoded by the EDAR gene. EDAR is a cell surface receptor for ectodysplasin A which plays an important role in the development of ectodermal tissues such as the skin. [1] [2] [3] It is structurally related to members of the TNF receptor superfamily. [4]
EDAR and other genes provide instructions for making proteins that work together during embryonic development. These proteins form part of a signaling pathway that is critical for the interaction between two cell layers, the ectoderm and the mesoderm. In the early embryo, these cell layers form the basis for many of the body's organs and tissues. Ectoderm-mesoderm interactions are essential for the proper formation of several structures that arise from the ectoderm, including the skin, hair, nails, teeth, and sweat glands. [3]
Mutation in this gene have been associated with hypohidrotic ectodermal dysplasia, a disorder characterized by a lower density of sweat glands. [3]
A derived G-allele point mutation (SNP) with pleiotropic effects in EDAR, 370A or rs3827760, found in ancient and modern East Asians, Southeast Asians, Nepalese [5] and Native Americans but not common in African or European populations. Experimental research in mice has linked the derived allele to a number of traits, including greater hair shaft diameter, more numerous sweat glands, smaller mammary fat pad, and increased mammary gland density. [6]
A 2013 study suggested that the EDAR variant (370A) arose about 35,000 years ago in central China, period during which the region was then quite warm and humid. [7] A subsequent study from 2021, based on ancient DNA samples, has suggested that the derived variant became dominant among "Ancient Northern East Asians" shortly after the Last Glacial Maximum in Northeast Asia, around 19,000 years ago. Ancient remains from Northern East Asia, such as the Tianyuan Man (40,000 years old) and the AR33K (33,000 years old) specimen lacked the derived EDAR allele, while ancient East Asian remains after the LGM carry the derived EDAR allele. [8] [9] The frequency of 370A is most highly elevated in North Asian and East Asian populations. [10] In a study of 222 Korean and 265 Japanese subjects, the 370A mutation was found in 86.9% Korean (Busan) and 77.5% Japanese (Tokyo) subjects. [11] This mutation is also implicated in ear morphology differences and reduced chin protrusion. [12]
It has been hypothesized that natural selection favored this allele during the last ice age in a population of people living in isolation in Beringia, as it may play a role in the synthesis of Vitamin D-rich breast milk in dark environments. [13] [14] [15] One study suggested that because the EDAR mutation arose in a cool and dry environment, it may have been adaptive by increasing skin lubrication, thus reducing dryness in exposed facial structures. [16]
The derived G-allele is a variation of the A-allele in earlier hominids, the version found in most modern non-East Asian and non-Native American populations and is found in 100% of Native American skeletal remains within all Native American haplogroups which studies have been done on prior to all contract for foreign population from Africa, Europe, or Asia. The derived allele was present in both the Tibeto-Burman (Magar and Newar) and Indo-European (Brahmin) populations of Nepal. The highest 1540C allele frequency was observed in Magar (71%), followed by Newar (30%) and Brahmin (20%). [5]
Derived variants of EDAR are associated with multiple facial and dental characteristics, such as shovel-shaped incisors. [17] [18] [19] [20]
50% of ancient DNA samples (7,900-7,500 BP) from Motala, Sweden; two (3300–3000 BC) from the Afanasevo culture and one (400–200 BC) Scythian sample were found to carry the rs3827760 mutation. [21]
According to a 2018 study, several ancient DNA samples from the Americas, including USR1 from the Upward Sun River site, Anzick-1, and the 9,600 BP individual from Lapa do Santo, were found to not carry the derived allele. This suggests that the increased frequency of the derived allele occurred independently in both East Asia and the Americas. [22]
A 2021 study analyzed the DNA of 6 Jomon remains from Japan and found that none of them carried the derived EDAR allele that is fixed in modern East Asian populations. [23]
The ectoderm is one of the three primary germ layers formed in early embryonic development. It is the outermost layer, and is superficial to the mesoderm and endoderm. It emerges and originates from the outer layer of germ cells. The word ectoderm comes from the Greek ektos meaning "outside", and derma meaning "skin".
In genetics and bioinformatics, a single-nucleotide polymorphism is a germline substitution of a single nucleotide at a specific position in the genome. Although certain definitions require the substitution to be present in a sufficiently large fraction of the population, many publications do not apply such a frequency threshold.
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Black hair is the darkest and most common of all human hair colors globally, due to large populations with this trait. This hair type contains a much more dense quantity of eumelanin pigmentation in comparison to other hair colors, such as brown, blonde and red. In English, various types of black hair are sometimes described as soft-black, raven black, or jet-black. The range of skin colors associated with black hair is vast, ranging from the palest of light skin tones to dark skin. Black-haired humans can have dark or light eyes.
Ectrodactyly–ectodermal dysplasia–cleft syndrome, or EEC, and also referred to as EEC syndrome and split hand–split foot–ectodermal dysplasia–cleft syndrome is a rare form of ectodermal dysplasia, an autosomal dominant disorder inherited as a genetic trait. EEC is characterized by the triad of ectrodactyly, ectodermal dysplasia, and facial clefts. Other features noted in association with EEC include vesicoureteral reflux, recurrent urinary tract infections, obstruction of the nasolacrimal duct, decreased pigmentation of the hair and skin, missing or abnormal teeth, enamel hypoplasia, absent punctae in the lower eyelids, photophobia, occasional cognitive impairment and kidney anomalies, and conductive hearing loss.
Amastia refers to a rare clinical anomaly in which both internal breast tissue and the visible nipple are absent on one or both sides. It affects both men and women. Amastia can be either isolated or comorbid with other syndromes, such as ectodermal dysplasia, Syndactyly and lipoatrophic diabetes. This abnormality can be classified into various types, and each could result from different pathologies. Amastia differs from amazia and athelia. Amazia is the absence of one or both mammary glands but the nipples remain present, and athelia is the absence of one or both nipples, but the mammary gland remains.
Hypohidrotic ectodermal dysplasia is one of about 150 types of ectodermal dysplasia in humans. Before birth, these disorders result in the abnormal development of structures including the skin, hair, nails, teeth, and sweat glands.
Shovel-shaped incisors are incisors whose lingual surfaces are scooped as a consequence of lingual marginal ridges, crown curvature, or basal tubercles, either alone or in combination.
Hay–Wells syndrome is one of at least 150 known types of ectodermal dysplasia. These disorders affect tissues that arise from the ectodermal germ layer, such as skin, hair, and nails.
NF-kappa-B essential modulator (NEMO) also known as inhibitor of nuclear factor kappa-B kinase subunit gamma (IKK-γ) is a protein that in humans is encoded by the IKBKG gene. NEMO is a subunit of the IκB kinase complex that activates NF-κB. The human gene for IKBKG is located on the chromosome band Xq28. Multiple transcript variants encoding different isoforms have been found for this gene.
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Gap junction beta-6 protein (GJB6), also known as connexin 30 (Cx30) — is a protein that in humans is encoded by the GJB6 gene. Connexin 30 (Cx30) is one of several gap junction proteins expressed in the inner ear. Mutations in gap junction genes have been found to lead to both syndromic and nonsyndromic deafness. Mutations in this gene are associated with Clouston syndrome.
GATA3 is a transcription factor that in humans is encoded by the GATA3 gene. Studies in animal models and humans indicate that it controls the expression of a wide range of biologically and clinically important genes.
Ectodysplasin A (EDA) is a protein that in humans is encoded by the EDA gene.
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Ectodysplasin-A receptor-associated adapter protein is a protein that in humans is encoded by the EDARADD gene.
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Hypohidrotic/anhidrotic ectodermal dysplasia with immune deficiency is a rare genetic condition characterized by a combination of the features of ectodermal dysplasia alongside immunodeficiency.
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