Clinical and molecular characterization of familial exudative vitreoretinopathy associated with microcephaly

PURPOSE: Familial exudative vitreoretinopathy (FEVR) is a rare finding in patients with genetic forms of microcephaly. This study documents the detailed phenotype and expands the range of genetic heterogeneity. Design; Retrospective case-series METHODS: Twelve patients (ten families) with a diagnosis of FEVR and microcephaly were ascertained from pediatric genetic eye clinics and underwent full clinical assessment including retinal imaging. Molecular investigations included candidate gene Sanger sequencing, whole-exome sequencing (WES) and whole-genome sequencing (WGS).

RESULTS: All patients had reduced vision and nystagmus. Six were legally blind. Two probands carried bi-allelic LRP5 variants, both presenting with bilateral retinal folds. A novel homozygous splice variant, and two missense variants were identified. Subsequent bone density measurement, identified osteoporosis in one proband.Four families had heterozygous KIF11 variants. Two probands had a retinal fold in one eye and chorioretinal atrophy in the other; the other two had bilateral retinal folds. Four heterozygous variants were found, including two large deletions not identified on Sanger sequencing or WES.Finally, a family of two children with learning difficulties, abnormal peripheral retinal vasculogenesis and rod-cone dystrophy were investigated. They were found to have bi-allelic splicing variants in TUBGCP6.Three families remain unsolved following WES and WGS.

CONCLUSIONS: Molecular diagnosis has been achieved in seven of ten families investigated including a previously unrecognized association with LRP5. WGS enabled molecular diagnosis in three families after prior negative Sanger sequencing of the causative gene. This has enabled patient-specific care with targeted investigations and accurate family counseling.