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L. Gradstein, E.J. FitzGibbon, J.F. Hejtmancik, J. Tang, R.C. Caruso, D. Blain, B.P. Brooks; Atypical Phenotype and Genotype in a Family With Suspected X–Linked Ocular Albinism . Invest. Ophthalmol. Vis. Sci. 2006;47(13):2508.
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© ARVO (1962-2015); The Authors (2016-present)
X–linked ocular albinism (XLOA) caused by mutations in OA1 gene on chromosome Xp22.3 is typically characterized by ocular hypopigmentation, low vision and nystagmus. We present a family suspected of having XLOA without nystagmus and investigate molecular mechanisms responsible for it.
Five members of a family with suspected XLOA underwent a complete ophthalmic examination. The affected 9–year old male proband had also eye movement and flash visual evoked potentials (VEP) recordings. Linkage analysis with OA1 region flanking polymorphic microsatellite markers (DXS7108, DXS8051) was performed on 5 family members. Direct sequence analysis of the coding region of the OA1 gene of the proband was carried out using automated fluorescence dideoxy method.
The proband had a visual acuity of 20/100 OD and 20/80 OS, mild hyperopia and no clinically discernable nystagmus. He showed iris transillumination, mild lenticular opacities, fundus hypopigmentation and foveal hypoplasia confirmed by the optical coherence tomography. Eye movement recordings confirmed no nystagmus and revealed fixation instability with square–wave jerks and fine drift. VEP detected excessive decussation of the optic nerve fibers at the chiasm typical of albinism. The proband’s mother had a visual acuity of 20/20, no nystagmus, scattered iris transillumination defects and patchy fundus hypopigmentation. The examination of other family members revealed normal eyes except for a mild juvenile cataract, transmitted in an autosomal dominant fashion through the paternal line, seemingly unrelated to the albinism. The analysis with the OA1 region flanking markers was consistent with linkage to this region on chromosome X; however a direct sequencing of the gene failed to identify any causative mutation in the entire OA1 coding sequence of the proband.
Although nystagmus is a prominent clinical feature in most individuals with XLOA, some patients may not display it and rather have a mild fixation instability noted only with eye movement recordings. Lack of causative mutation in the coding sequence of the OA1 gene of the proband requires further investigation in order to elucidate the genetic mechanism responsible for albinism in this family.
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