Homozygous single nucleotide duplication of SLC38A8 in autosomal recessive foveal hypoplasia: The first Japanese case report.

Purpose: To characterize the clinical and genetic features of a Japanese male patient with foveal hypoplasia caused by a homozygous single nucleotide duplication in the SLC38A8 gene. Methods: We performed a comprehensive ophthalmic examination including full-field electroretinography (FF-ERG) and pattern-reversal visual evoked potentials (PR-VEPs). Whole-exome sequencing (WES) was performed to identify the disease-causing variant; Sanger sequencing was used for confirmation. Results: In the WES analysis, a homozygous single nucleotide duplication (c.995dupG; p.Trp333MetfsTer35) was identified in SLC38A8 of the patient. His unaffected mother carried the variant heterozygously. The patient exhibited hyperopia, congenital nystagmus, low visual acuity, and grade 4 foveal hypoplasia. Slit-lamp examination revealed mild posterior embryotoxon and goniodysgenesis. Fundus examination revealed the absence of foveal hyperpigmentation and foveal avascularity, but there were no retinal degenerative lesions. In the FF-ERG, the amplitudes of rod ERG, standard-flash, and bright-flash ERG were within the normal range; cone-mediated responses also showed nearly normal amplitudes. The PR-VEP findings revealed delayed P100 latencies and decreased amplitudes of the P100 components, but no chiasmal misrouting. Conclusions: This report is the first report on the clinical and genetic characteristics of SLC38A8-associated foveal hypoplasia in the Japanese population. This is also the first report of normal rod- and cone-mediated responses in a patient with this disorder. [ABSTRACT FROM AUTHOR]