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To date, over 150 disease-associated variants in CRB1 have been described, resulting in a range of retinal disease phenotypes including Leber congenital amaurosis and retinitis pigmentosa. Despite this, no genotype-phenotype correlations are currently recognised. We performed a retrospective review of electronic patient records to identify patients with macular dystrophy due to bi-allelic variants in CRB1. In total, seven unrelated individuals were identified. The median age at presentation was 21 years, with a median acuity of 0.55 decimalised Snellen units (IQR = 0.43). The follow-up period ranged from 0 to 19 years (median = 2.0 years), with a median final decimalised Snellen acuity of 0.65 (IQR = 0.70). Fundoscopy revealed only a subtly altered foveal reflex, which evolved into a bull's-eye pattern of outer retinal atrophy. Optical coherence tomography identified structural changes-intraretinal cysts in the early stages of disease, and later outer retinal atrophy. Genetic testing revealed that one rare allele (c.498_506del, p.(Ile167_Gly169del)) was present in all patients, with one patient being homozygous for the variant and six being heterozygous. In trans with this, one variant recurred twice (p.(Cys896Ter)), while the four remaining alleles were each observed once (p.(Pro1381Thr), p.(Ser478ProfsTer24), p.(Cys195Phe) and p.(Arg764Cys)). These findings show that the rare CRB1 variant, c.498_506del, is strongly associated with localised retinal dysfunction. The clinical findings are much milder than those observed with bi-allelic, loss-of-function variants in CRB1, suggesting this in-frame deletion acts as a hypomorphic allele. This is the most prevalent disease-causing CRB1 variant identified in the non-Asian population to date.

Familial hyperaldosteronism type II (FH-II) is an inherited form of hyperaldosteronism associated with hypertension in most patients. The mutations that cause FH-II are unknown, but linkage analysis has mapped them to chromosome 7p22. As FH-II is clinically indistinguishable from sporadic primary aldosteronism, a common and treatable condition, unravelling the cause of FH-II has important implications for these sporadic cases. To investigate whether FH-II is caused by large deletions or insertions, we examined the virtual karyotype of four pairs of affected and unaffected individuals using high-density bead chips. We also sequenced the coding regions of five 7p22 candidate genes that were prioritized because of their putative role in cell growth. We found no evidence of single-nucleotide polymorphism (SNP) copy number variation between pairs, and from the widest gap on the chip, chromosome 7p22 deletions or insertions exceeding ∼50 kb in these pedigrees can be excluded. We found 15 SNPs (two of which were novel), but none of them were non-synonymous and segregated with the disease in the FH-II pedigrees. We have been able to exclude large genomic deletions or insertions at 7p22 and refine the candidate gene list for this locus, but the mutations causing FH-II remain elusive.