Targeted next-generation sequencing identifies a homozygous nonsense mutation in ABHD12, the gene underlying PHARC, in a family clinically diagnosed with Usher syndrome type 3
1 Bioscientia Center for Human Genetics, Konrad Adenauer-Str. 17, Ingelheim 55218, Germany
2 Department of Human Genetics, McGill University Health Center, Montreal, Canada
3 Department of Obstetrics and Gynecology, McGill University Health Center, Montreal, Canada
4 Department of Ophthalmology, American University of Beirut, Beirut, Lebanon
5 Center for Molecular Medicine Cologne, University of Cologne, Cologne, Germany
6 Cologne Center for Genomics, University of Cologne, Cologne, Germany
7 Institute of Human Genetics, University Hospital of Cologne, Cologne, Germany
8 Department of Human Genetics, RWTH Aachen University, Aachen, Germany
9 Center for Clinical Research, University Hospital of Freiburg, Freiburg, Germany
Orphanet Journal of Rare Diseases 2012, 7:59 doi:10.1186/1750-1172-7-59Published: 2 September 2012
Usher syndrome (USH) is an autosomal recessive genetically heterogeneous disorder with congenital sensorineural hearing impairment and retinitis pigmentosa (RP). We have identified a consanguineous Lebanese family with two affected members displaying progressive hearing loss, RP and cataracts, therefore clinically diagnosed as USH type 3 (USH3). Our study was aimed at the identification of the causative mutation in this USH3-like family.
Candidate loci were identified using genomewide SNP-array-based homozygosity mapping followed by targeted enrichment and next-generation sequencing.
Using a capture array targeting the three identified homozygosity-by-descent regions on chromosomes 1q43-q44, 20p13-p12.2 and 20p11.23-q12, we identified a homozygous nonsense mutation, p.Arg65X, in ABHD12 segregating with the phenotype.
Mutations of ABHD12, an enzyme hydrolyzing an endocannabinoid lipid transmitter, cause PHARC (polyneuropathy, hearing loss, ataxia, retinitis pigmentosa, and early-onset cataract). After the identification of the ABHD12 mutation in this family, one patient underwent neurological examination which revealed ataxia, but no polyneuropathy. ABHD12 is not known to be related to the USH protein interactome. The phenotype of our patient represents a variant of PHARC, an entity that should be taken into account as differential diagnosis for USH3. Our study demonstrates the potential of comprehensive genetic analysis for improving the clinical diagnosis.