Expanding the clinical, allelic, and locus heterogeneity of retinal dystrophies.

PURPOSE: Retinal dystrophies (RD) are heterogeneous hereditary disorders of the retina that are usually progressive in nature. The aim of this study was to clinically and molecularly characterize a large cohort of RD patients. METHODS: We have developed a next-generation sequencing assay that allows known RD genes to be sequenced simultaneously. We also performed mapping studies and exome sequencing on familial and on syndromic RD patients who tested negative on the panel. RESULTS: Our panel identified the likely causal mutation in >60% of the 292 RD families tested. Mapping studies on all 162 familial RD patients who tested negative on the panel identified two novel disease loci on Chr2:25,550,180-28,794,007 and Chr16:59,225,000-72,511,000. Whole-exome sequencing revealed the likely candidate as AGBL5 and CDH16, respectively. We also performed exome sequencing on negative syndromic RD cases and identified a novel homozygous truncating mutation in GNS in a family with the novel combination of mucopolysaccharidosis and RD. Moreover, we identified a homozygous truncating mutation in DNAJC17 in a family with an apparently novel syndrome of retinitis pigmentosa and hypogammaglobulinemia. CONCLUSION: Our study expands the clinical and allelic spectrum of known RD genes, and reveals AGBL5, CDH16, and DNAJC17 as novel disease candidates.Genet Med 18 6, 554-562.

Autozygome maps dispensable DNA and reveals potential selective bias against nullizygosity.

PURPOSE: Copy number variants are an important source of human genome diversity. The widespread distribution of hemizygous copy number variants in the DNA of healthy humans suggests that haploinsufficiency is largely tolerated. However, little is known about the extent to which corresponding nullizygosity (two-copy deletion) is similarly tolerated. METHODS: We analyzed a cohort of first cousin unions to enrich for shared parental hemizygous events and tested their Mendelian inheritance in offspring. RESULTS: Analysis of autozygous DNA blocks (autozygome) in the offspring not only proved an efficient method of mapping "dispensable" DNA but also revealed potential selective bias against the occurrence of nullizygous changes. This bias was not restricted to genic copy number variants and was not accounted for by a high rate of miscarriages. CONCLUSIONS: The autozygome is an efficient way to map dispensable segments of DNA and may reveal selective bias against nullizygosity in healthy individuals.