ABSTRACT
BACKGROUND: Congenital long QT syndrome (LQTS) is an inherited, potentially fatal arrhythmogenic disorder. At least 16 genes have been implicated in LQTS; the yield of genetic analysis of 3 genes (KCNQ1, KCNH2, and SCN5A) is about 70%, with KCNQ1 mutations accounting for â¼50% of positive cases. LQTS is mostly inherited in an autosomal dominant pattern. Systemic analysis of LQTS has not been previously conducted in a population with a high degree of consanguinity. OBJECTIVES: To describe the clinical and molecular profiles of LQTS in the highly consanguineous Saudi population. METHODS: Fifty-six Saudi families with LQTS were consecutively recruited and evaluated. Sequencing of KCNQ1, KCNH2, and SCN5A genes was conducted on all probands, followed by screening of family relatives. RESULTS: Genetic analysis was positive in 32 (57.2%) families, with mutations in KCNQ1 identified in 28 families (50%). Surprisingly, 17 (53.1%) probands were segregating homozygous mutations. Family screening identified 123 individuals with mutations; 89 (72.4%) were heterozygous, 23 (18.7%) were homozygous, and 11 (8.9%) were compound heterozygous. Compared to heterozygous, the phenotype was more severe in homozygous individuals, with cardiac symptoms in 78.3% (vs 12.4%), family history of sudden death in 64.7% (vs 44.4%), and prolonged QT interval in 100% (vs 43.8%). Congenital deafness was found in 11 (47.8%) homozygous probands. CONCLUSION: Our study provides insight into the clinical and molecular profiles of LQTS in a consanguineous population. It underscores the importance of preemptive management in homozygous patients with LQTS and the value of clinical and molecular screening of at-risk relatives.
Subject(s)
Consanguinity , Genetic Testing/methods , Long QT Syndrome/genetics , Adolescent , Adult , Child , Child, Preschool , Female , Follow-Up Studies , Genotype , Heterozygote , Homozygote , Humans , Incidence , Infant , Infant, Newborn , Long QT Syndrome/epidemiology , Male , Middle Aged , Pedigree , Phenotype , Retrospective Studies , Saudi Arabia/epidemiology , Survival Rate/trends , Young AdultABSTRACT
Desbuquois dysplasia is an autosomal recessive dysplasia characterized by severe growth restriction and distinct hand and proximal femur appearance in addition to cognitive impairment. The critical interval for this disease has been mapped to 17q25.3 using homozygosity mapping. We have identified a newborn with classical features of the disease whose parents are first cousins. Assuming genetic homogeneity of this disorder, we were able to narrow the critical interval to a region that only contained 10 annotated genes by combining the results of our homozygosity mapping with those of others. Serial sequencing of the genes contained within the interval revealed a 5 bp duplication in Calcium-Activated Nucleotidase 1 gene (CANT1), consistent with the very recent report by Huber et al. [Huber et al. (2009); Am J Hum Genet 85:706-710]. This report cements the role of CANT1 in the causation of this dysplasia and demonstrates the high value of even single cases in the setting of genetically homogeneous disorders when homozygosity mapping is used.
