Albinism, Oculocutaneous, type IA; OCA1A

What is Albinism, Oculocutaneous, type IA; OCA1A?

Albinism, Oculocutaneous, type IA; OCA1A is a rare disease. It is also known as Albinism - temperature sensitive Albinism I OCA OCA1 OCA2 OCA3 OCA4 Oculo-cutaneous albinism Oculocutaneous albinism - type I Oculocutaneous Albinism, Type I; Oca1 Oculocutaneous Albinism, Tyrosinase-negative; Atn.

In its simplest form there are at least two types of oculocutaneous albinism (OCA), and there is good evidence from chance matings between those with albinism who produce normally pigmented offspring of there being more types. It is difficult clinically to distinguish between the type I (tyrosinase negative) albinism and the type II (tyrosinase positive) albinism. However, in type II pigmented nevi can occur (Akiyama et al., 1992), and in black people the hair tends to be slightly yellow. In type I iris translucency occurs in about 70% of carriers, and even the skin and hair can be mildly involved. Visual handicap occurs in most homozygotes, although only 20% need special educational facilities because of visual problems. Greater than 50% of optic nerve fibres cross the optic chiasma, causing problems with binocular vision. The fovea is poorly developed and photophobia and nystagmus occur. Biswas and Lloyd (1999) provide a good review of the ocular features. Holmes and Cronin (1991) reported a case with Duane syndrome. Bodensteiner et al., (1990) reported a girl with ocular albinism and a hypoplastic corpus callosum. They postulated a general defect of neuronal migration associated with albinism. Gül et al., (2000 reported two sibs with oculocutaneous albinism together with evidence of osteopenia, but only on bone scanning. Intelligence was normal.
Type I OCA is uncommon in African and Afro-American black individuals, whereas type II OCA is quite common in this group.
Type I OCA maps to 11q14-21 and has been shown to be caused by a deficiency of the enzyme tyrosinase. Type II OCA maps to 15q11-12 (Ramsay et al., 1992). Lee et al., (1994) demonstrated mutations in the P gene (the homologue of the mouse pink-eye dilution (p) gene) in three patients with type II OCA, one of whom also had Prader-Willi syndrome. Lee et al., (1994) reported mutations in seven unrelated African-American patients with type II OCA. There were three large deletions, two small in-frame deletions and six different point mutations. Stevens et al., (1995) and Spritz et al., (1995) also found an intragenic deletion in 75-80% of mutant alleles in the African Bantu population, where the overall prevalence of the disorder is 1 in 1,400-3,900. Lund (1996) and Puri et al., (1997) found a similar prevalence in Zimbabwe and review other studies of the condition in Africa. Mutations in the P gene in the German population were reported by Passmore et al., (1999). Ti et al., (2003) showed that a 122.5-kilobase deletion in the P gene is responsible for the high prevalence of OCA2 in the Navajo population. The P protein is a transmembrane polypeptide that may transport small molecules such as tyrosine.
Boissy et al., (1996) reported mutations in a further type of oculocutaneous albinism, brown OCA, which in black individuals presents with light brown skin, light hair and blue to brown irises associated with nystagmus. The condition has not yet been reported in caucasians. Boissy et al., (1996) demonstrated a mutation in the tyrosinase related protein-1 (TYRP1) gene. This gene maps to 9p23. Manga et al., (2001) found mutations in the OCA2 gene at 15q in individuals with brown oculocutaneous albinism. Of ten unrelated individuals nine had a 2.7-kb deletion in one copy of the gene. No other mutations were identified.
King et al., (2003) identified eight probands with oculocutaneous albinism (OCA) who had red hair at birth. Mutations in the P gene (OCA2) were identified in all eight, and mutations in the MC1R gene were responsible for the red (rather than yellow/blond) hair in the six of eight who continued to have red hair after birth. OCA2 can be clinically, very mild, and a Japanese man reported by Kawai et al., (2005) was only recognized when he developed extensive sun burn blistering. He had mild skin hypopigmentation, but normal hair and eye colour.
Ruferous albinism is similar to brown OCA. It has mainly been reported in black populations. The skin colour is brick red, mahogany, or bronze and the hair is ginger or reddish brown. the irises are blue or brown and visual anomalies are mild with about 75% of cases having nystagmus. Manga et al., (1997) mapped this gene to 9p23 and demonstrated mutations in the TYRP1 gene.
Spritz (1994) provides a good review of the molecular pathology. Prenatal diagnosis of oculocutaneous albinism has depended on fetal skin biopsy with EM examination, however DNA methods are now becoming available (Falik-Borenstein et al., 1995).
Newton et al., (2001) demonstrated mutations in a gene encoding protein MATP4 (membrane-associated-transporter-protein). In a a rare form of oculocutaneous albinism - OCA4 mutations in the same gene cause the mouse phenotype uw - underwhite.
Mutations in C10orf11 in a number of individuals from the Faroe Islands and one originally from Lithuania have been reported (Gronskov et al., 2013) to also cause albinism.
A large inbred Pakistani family (Kausar et al., 2013) whose affected members had golden hair, white skin, nystagmus, photophobia, foveal hypoplasia, mapped to 4q24

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* This information is courtesy of the L M D.

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What gene changes cause Albinism, Oculocutaneous, type IA; OCA1A?

The syndrome is inherited in the following inheritance pattern/s:

Autosomal Recessive - Autosomal recessive inheritance means an affected individual receives one copy of a mutated gene from each of their parents, giving them two copies of a mutated gene. Parents, who carry only one copy of the gene mutation will not generally show any symptoms but have a 25% chance of passing the copies of the gene mutations onto each of their children.

In some cases, a genetic syndrome may be the result of a de-novo mutation and the first case in a family. In this case, this is a new gene mutation that occurs during the reproductive process.

OMIM Number - 203100 (please check the OMIM page for updated information)

The syndrome can be caused by mutations in the following gene/s location/s:
TYR - 11q14.3

What are the main symptoms of Albinism, Oculocutaneous, type IA; OCA1A?

The typical symptoms of the syndrome are:
Albinism, Aplasia/Hypoplasia of the corpus callosum, Astigmatism, Abnormality of visual evoked potentials, Blue irides, White hair, Absent skin pigmentation, Strabismus, Reduced bone mineral density, Congenital onset, Myopia, Neoplasm of the skin, Freckling, Hypoplasia of the fovea, Generalized hypopigmentation, Hyperkeratosis, Visual impairment, Autosomal recessive inheritance, Photophobia, Ocular albinism, Optic atrophy, Nystagmus

How does someone get tested for Albinism, Oculocutaneous, type IA; OCA1A?

The initial testing for Albinism, Oculocutaneous, type IA; OCA1A can begin with facial genetic analysis screening, through the FDNA Telehealth telegenetics platform, which can identify the key markers of the syndrome and outline the type of genetic testing needed. A consultation with a genetic counselor and then a geneticist will follow.

Based on this clinical consultation with a geneticist, the different options for genetic testing will be shared and consent will be sought for further testing.

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