Our comprehensive cohort of 1100 unrelated achromatopsia (ACHM) patients comprises
a considerable number of cases (~5%) harboring only a single pathogenic variant in
the major ACHM gene CNGB3. We sequenced the entire CNGB3 locus in 33 of these patients
in order to find a second variant which eventually explained the patients' phenotype.
Forty-seven intronic CNGB3 variants were identified in 28 subjects after a filtering
step based on frequency and the exclusion of variants found in cis with pathogenic
alleles. In a second step, in silico prediction tools were used to filter out those
variants with little odds of being deleterious. This left three variants that were
analysed using heterologous splicing assays. Variant c.1663-1205G>A, found in 14 subjects,
and variant c.1663-2137C>T, found in two subjects, were indeed shown to exert a splicing
defect by causing pseudoexon insertion into the transcript. Subsequent screening of
further unsolved CNGB3 subjects identified four additional cases harboring the c.1663-1205G>A
variant which makes it the eighth most frequent CNGB3 variant in our cohort. Compound
heterozygosity could be validated in ten cases. Our study demonstrates that whole
gene sequencing can be a powerful approach to identify the second pathogenic allele
in patients apparently harboring only one disease-causing variant. This article is
protected by copyright. All rights reserved.
