Next generation sequencing uncovers a missense mutation in COL4A1 as the cause of familial retinal arteriolar tortuosity.

OBJECTIVES: Our aim was to determine the molecular cause of autosomal dominant familial retinal arteriolar tortuosity (FRAT) in a family with three affected subjects. MATERIAL AND METHODS: Ophthalmologic evaluation included determination of best-corrected visual acuity (BCVA), slit-lamp and dilated fundus inspection, applanation tonometry, fundus photography, and fluorescein retinal angiography (FA). Molecular methods included whole exome sequencing analysis and Sanger sequencing validation of putative causal mutation in DNA from affected individuals. RESULTS: Typical signs of familial retinal arteriolar tortuosity were observed in all three patients. Exome sequencing identified a heterozygous c.1528G > A (p. Gly510Arg) mutation in COL4A1. Sanger sequencing confirmed that all three patients harbored the same pathogenetic mutation in COL4A1. The p. Gly510Arg variant in COL4A1 was absent in DNA from an available unaffected daughter, from a set of control alleles, and from publicly available databases. CONCLUSIONS: The molecular basis of familial retinal arteriolar tortuosity was identified for the first time, thus expanding the human phenotypes linked to COL4A1 mutations. Interestingly, the COL4A1 p.Gly510Arg mutation has been previously identified in a family with HANAC (Hereditary Angiopathy with Nephropathy, Aneurysm and Cramps), a multisystemic disease featuring retinal arteriolar tortuosity. No cerebral, neurologic, renal, cardiac or vascular anomalies were recognized in the pedigree described here. These data indicate that identical mutations in COL4A1 can originate both eye-restricted and systemic phenotypes.

A novel mutation confirms MFRP as the gene causing the syndrome of nanophthalmos-renititis pigmentosa-foveoschisis-optic disk drusen.

PURPOSE: To describe the clinical and genetic characteristics of the second family with a recently described recessive syndrome characterized by posterior microphthalmos, retinitis pigmentosa, foveoschisis, and optic disk drusen. DESIGN: Observational case report. METHODS: Three affected subjects and one healthy sibling from a consanguineous marriage from Spain were studied. Complete ophthalmologic examinations including A- and B-mode ultrasonography (US), electroretinography (ERG), fluorescein retinal angiography (FA), and optical coherence tomography (OCT) were performed in each individual. Genetic analysis included polymerase chain reaction amplification and direct nucleotide sequencing of the complete MFRP gene. RESULTS: All three affected siblings had bilateral shortening of the posterior ocular segment associated with high hyperopia and normal anterior segment dimensions. Best-corrected visual acuity ranged from 20/200 to 20/60. Funduscopy, ERG, and FA were compatible with retinitis pigmentosa, and B-mode ultrasound showed optic disk drusen. OCT analysis revealed outer retinal layer schisis with absence of foveal pit. Inheritance of this syndrome followed an autosomal recessive pattern. Molecular analysis revealed a novel homozygous 1-bp deletion (c.498delC) in exon 5 of MFRP, predicting a prematurely truncated protein (P166fsX190). A healthy sister demonstrated to be a carrier of the mutation. CONCLUSIONS: We confirmed that the syndrome of posterior microphthalmos, retinitis pigmentosa, foveoschisis, and optic disk drusen constitutes a distinct autosomal recessive entity. The novel frameshift mutation identified in the family described here validates MFRP as the gene responsible for this particular disease, which characteristically involves structures located at the posterior segment of the eye.