Patient Population and Genetic Analysis

Patients with bi-allelic molecularly confirmed pathogenic variants in LRAT were collected from the database for hereditary eye diseases (Delleman archive) at the Academic Medical Center (AMC) in Amsterdam, the Netherlands, resulting in a cohort of 12 patients from a Dutch genetic isolate. One Turkish–Belgian patient (Turkish descent) was included from Ghent University Hospital, Belgium. Informed consent was obtained from Dutch patients in this study, and the study adhered to the tenets of the Declaration of Helsinki. For the Belgian patient, informed consent for this retrospective study was waivered by the Ethics Committee of Ghent University Hospital.

Mutational analyses for Dutch patients were performed at the AMC, and at the Ghent University Hospital for the Belgian patient. In the Dutch patients, no pathogenic variants were found with the autosomal recessive RP chip (version 2011/2012; Asper Biotech, Tartu, Estonia), which included RPE65, but sequence analysis of LRAT revealed a previously described homozygous frameshift mutation,28 which led to a premature stop codon (c.12del; p.[Met5Cysfs*53]; {"type":"entrez-nucleotide","attrs":{"text":"NM_004744.4","term_id":"675022747","term_text":"NM_004744.4"}}NM_004744.4), and segregated with the disease. Because the Dutch patients originated from the same genetic isolate as the previously described CRB1-RP cohorts,29,30 the presence of bi-allelic CRB1 mutations was excluded in all patients. The Turkish–Belgian patient carried a homozygous missense mutation in LRAT (c.326G>T; p.[Arg109Leu]), found through identity by descent–guided Sanger sequencing,31 and a heterozygous rare variant in CRB1 (c.4060G>A; p.[Ala1354Thr]), found with LCA chip analysis. Sanger sequencing of the coding regions and intron–exon borders revealed no second CRB1 mutation.