PT - JOURNAL ARTICLE AU - Claire Redin AU - Stéphanie Le Gras AU - Oussema Mhamdi AU - Véronique Geoffroy AU - Corinne Stoetzel AU - Marie-Claire Vincent AU - Pietro Chiurazzi AU - Didier Lacombe AU - Ines Ouertani AU - Florence Petit AU - Marianne Till AU - Alain Verloes AU - Bernard Jost AU - Habiba Bouhamed Chaabouni AU - Helene Dollfus AU - Jean-Louis Mandel AU - Jean Muller TI - Targeted high-throughput sequencing for diagnosis of genetically heterogeneous diseases: efficient mutation detection in Bardet-Biedl and Alström Syndromes AID - 10.1136/jmedgenet-2012-100875 DP - 2012 Aug 01 TA - Journal of Medical Genetics PG - 502--512 VI - 49 IP - 8 4099 - http://jmg.bmj.com/content/49/8/502.short 4100 - http://jmg.bmj.com/content/49/8/502.full SO - J Med Genet2012 Aug 01; 49 AB - Background Bardet-Biedl syndrome (BBS) is a pleiotropic recessive disorder that belongs to the rapidly growing family of ciliopathies. It shares phenotypic traits with other ciliopathies, such as Alström syndrome (ALMS), nephronophthisis (NPHP) or Joubert syndrome. BBS mutations have been detected in 16 different genes (BBS1-BBS16) without clear genotype-to-phenotype correlation. This extensive genetic heterogeneity is a major concern for molecular diagnosis and genetic counselling. While various strategies have been recently proposed to optimise mutation detection, they either fail to detect mutations in a majority of patients or are time consuming and costly. Method We tested a targeted exon-capture strategy coupled with multiplexing and high-throughput sequencing on 52 patients: 14 with known mutations as proof-of-principle and 38 with no previously detected mutation. Thirty genes were targeted in total including the 16 BBS genes, the 12 known NPHP genes, the single ALMS gene ALMS1 and the proposed modifier CCDC28B. Results This strategy allowed the reliable detection of causative mutations (including homozygous/heterozygous exon deletions) in 68% of BBS patients without previous molecular diagnosis and in all proof-of-principle samples. Three probands carried homozygous truncating mutations in ALMS1 confirming the major phenotypic overlap between both disorders. The efficiency of detecting mutations in patients was positively correlated with their compliance with the classical BBS phenotype (mutations were identified in 81% of ‘classical’ BBS patients) suggesting that only a few true BBS genes remain to be identified. We illustrate some interpretation problems encountered due to the multiplicity of identified variants. Conclusion This strategy is highly efficient and cost effective for diseases with high genetic heterogeneity, and guarantees a quality of coverage in coding sequences of target genes suited for diagnosis purposes.