Paula and Bobby
Parents of Lillie
Albinism, Ocular, Type I
What is Albinism, Ocular, Type I?
Albinism, Ocular, Type I is a rare disease. It is also known as Nettleship-falls Type Ocular Albinism Nettleship-Falls type of ocular albinism OA1 Ocular albinism - X-linked.
Ocular features predominate although there is pigment dilution of skin and of hair as compared to unaffected relatives. Visual acuity is reduced with nystagmus and foveal hypoplasia. Rarely nystagmus may be absent and the acuity as good as 6/9. Iris translucency is common although not invariably present, especially if the irides are brown. The condition has a frequency of 1 in 60,000 live births (Oetting, 2002).
Posterior embryotoxon or Axenfeld anomaly occurs in about 1/3, but glaucoma is rare. More than half have a refractive error of more than 2 dioptres which may be hypermetropia or myopia. Astigmatism of more than 2 dioptres is very common. Best corrected distance vision is at least 6/36 in both eyes together, in about 80% of cases and more than 90% read N6+ either unaided or with a magnifier.
There is much variation even within a family. Giant spherical macromelanosomes are found in skin and ocular melanocytes in males and in 84% of carrier females which suggests that this may be a disorder of melanin secretion rather than a defect in synthesis.
Macromelanosomes are not unique to ocular albinism. In more than 90% of obligate heterozygotes there is a "mosaical" ocular fundus pigmentation with a "mud-splattered" appearance, or hyperpigmented streaks in the periphery. Winship et al., 1984, reported a large South African kindred with associated middle age onset sensorineural deafness in affected males.
The gene has been mapped to Xp22.3-22.2 and the gene has been cloned (Bassi et al., 1995). About 92% of obligate female carriers had a mud-splattered appearance of the fundus with hyperpigmented streaks. In 74% this was associated with iris translucency (Charles et al., 1992). Nineteen independent missense mutations were characterized by d'Addio et al., (2000). These authors found that a significant number of the mutations caused protein misfolding. Intagenic deletions occur in fewer than 10% of European patients, but in more than half of North American patients. A four generation family with a 29 bp deletion in exon 1, was reported by Rudolph et al., (2001). To date (Camand et al., 2003) 41 mutations have been reported. Heterozygous females show a 'mud-splattered' mosaic appearance. Some show so-called bear tracts (Costa et al., 2003).
Six Chinese families had GPR143 mutations (Fang et al., 2008).Of the 15 patients (15) only 1 had obvious iris hypopigmentation and 8 had normal fundal pigmentation. All had severe foveal hypoplasia.
* This information is courtesy of the L M D.
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What gene changes cause Albinism, Ocular, Type I?
The syndrome is inherited in the following inheritance pattern/s:
X-Linked Recessive - Syndromes inherited in an X-linked recessive pattern generally only affect males. Males only have one X chromosome, and so one copy of a gene mutation on it causes the syndrome. Females, with two X chromosomes, only one of which will be mutated, are not likely to be affected.
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 - 300500 (please check the OMIM page for updated information)
The syndrome can be caused by mutations in the following gene/s location/s:
GPR143 - Xp22.2
What are the main symptoms of Albinism, Ocular, Type I?
The typical symptoms of the syndrome are:
Nystagmus, Ocular albinism, Photophobia, Abnormal macular morphology, Abnormal pupil morphology, Astigmatism, Depigmented fundus, Strabismus, X-linked inheritance, Nystagmus-induced head nodding, Freckling, Giant melanosomes in melanocytes, Visual impairment, Neoplasm of the skin, Myopia
How does someone get tested for Albinism, Ocular, Type I?
The initial testing for Albinism, Ocular, Type I 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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