Use of genome-wide SNP homozygosity mapping in small pedigrees to identify new mutations in VSX2 causing recessive microphthalmia and a semidominant inner retinal dystrophy.

Mutations in the visual system homeobox 2 gene (VSX2, also known as CHX10), which encodes a retinal transcription factor from the paired homeobox family, have been implicated in recessive isolated microphthalmia. In this study, we use genome-wide single nucleotide polymorphism homozygosity mapping in unrelated small consanguineous pedigrees and a candidate gene approach to identify three further causative VSX2 mutations (two novel and one previously reported). All affected individuals with homozygous mutations had bilateral anophthalmia or severe microphthalmia with absent vision. In addition, we identified a novel inner retinal dystrophy in two carrier parents suggesting a semidominant effect for this particular VSX2 mutation. A further study of individuals with retinal degenerative conditions may reveal a causative role for heterozygous mutations in VSX2.

Seeing clearly: the dominant and recessive nature of FOXE3 in eye developmental anomalies.

FOXE3 is a lens-specific transcription factor with a highly conserved forkhead domain previously implicated in congenital primary aphakia and anterior segment dysgenesis. Here, we identify new recessive FOXE3 mutations causative for microphthalmia, sclerocornea, primary aphakia, and glaucoma in two extended consanguineous families by SNP array genotyping followed by a candidate gene approach. Following an additional screen of 236 subjects with developmental eye anomalies, we report two further novel heterozygous mutations segregating in a dominant fashion in two different families. Although the dominant mutations were penetrant, they gave rise to highly variable phenotypes including iris and chorioretinal colobomas, Peters' anomaly, and isolated cataract (cerulean type and early onset adult nuclear and cortical cataract). Using in situ hybridization in human embryos, we demonstrate expression of FOXE3 restricted to lens tissue, predominantly in the anterior epithelium, suggesting that the extralenticular phenotypes caused by FOXE3 mutations are most likely to be secondary to abnormal lens formation. Our findings suggest that mutations in FOXE3 can give rise to a broad spectrum of eye anomalies, largely, but not exclusively related to lens development, and that both dominant and recessive inheritance patterns can be represented. We suggest including FOXE3 in the diagnostic genetic screening for these anomalies.

Clinical and genetic features of PKAN patients in a tertiary centre in Turkey.

OBJECTIVE: Pantothenate kinase-associated neurodegeneration (PKAN) is caused by mutations of the pantothenate kinase 2 (PANK2) gene. The major clinical sign of PKAN is dystonia and the eye-of-the-tiger pattern on the MRI has been a clue for the diagnosis. We aim to discuss clinical and genetic findings of 22 PKAN patients from 13 families. METHODS: Twenty-two patients were clinically diagnosed with PKAN and screened for PANK2 mutations. The patients were classified according to their onset age and progression rate. RESULTS: Mutation screening revealed 5 novel and 7 previously reported sequence variants in PANK2. The variants identified were in the form of missense changes, small exonic deletions and intronic mutations with a probable splicing effect. The presenting features were dystonia and gait disturbance in early onset patients, whereas the presenting symptoms were variable for the late onset group. The progression rate of the disease was not uniform. CONCLUSION: The current report is the first patient series of PKAN from Turkey that expands the clinical and genetic spectrum of the disease.