Genetic screening of calcium regulation genes in familial hypertrophic cardiomyopathy.

Genes encoding Ca(2+) regulatory proteins responsible for Ca(2+) homeostasis have been suggested as possible candidates for FHC. Mutations in sarcomere genes account for approximately 50% of all FHC cases indicating other genes, including those involved in Ca(2+) handling, may account for the remainder. The aim of this study was to identify causative mutations in genes involved in Ca(2+) regulation in patients with familial hypertrophic cardiomyopathy (FHC). An Australian cohort of 252 unrelated familial hypertrophic cardiomyopathy patients were screened for mutations in the Ca(2+) regulatory genes, sorcin (SRI), calstabin (FKBP1B), calsequestrin (CASQ2), phospholamban (PLN), sarcolipin (SLN), calreticulin (CALR3) and calmodulin (CALM). A total of 17 exonic DNA variants were identified in the 7 Ca(2+) regulatory genes studied, of which 4 were considered of pathogenic significance. Two novel mutations in the CALR3 gene were identified (Lys82Arg, Arg73Gln) and one truncation mutation in the PLN gene (Leu39Ter). A variant was also identified in the CASQ2 gene (Asp63Glu). These four variants were all novel, resulted in changes in conserved amino acids and were not identified in a normal population. In conclusion, mutations in Ca(2+) handling genes are an infrequent but important cause of FHC. DNA variants in Ca(2+) genes may also be involved as modifying factors in phenotype development. Further evaluation of the role of defects in Ca(2+) regulation will shed light on the molecular pathogenesis of FHC.

Cardiac troponin I mutations in Australian families with hypertrophic cardiomyopathy: clinical, genetic and functional consequences.

BACKGROUND: Hypertrophic cardiomyopathy (HCM) is an autosomal dominant disorder caused by mutations in sarcomeric proteins. Cardiac troponin I (cTnI) is a key switch molecule in the sarcomere. Mutations in cTnI have been identified in <1% of genotyped HCM families. METHODS: To study the prevalence, clinical significance and functional consequences of cTnI mutations, genetic testing was performed in 120 consecutive Australian families with HCM referred to a tertiary referral centre, and results correlated with clinical phenotype. Each cTnI mutation identified was tested in a mammalian two-hybrid system to evaluate the functional effects of these mutations on troponin complex interactions. RESULTS: Disease-causing missense mutations were identified in four families (3.3%). Two mutations were located at the same codon in exon 7 (R162G, R162P), and two in exon 8 (L198P, R204H). All four mutations change amino acid residues which are highly conserved and were not found in normal populations. Follow-up family screening has identified a total of seven clinically affected members in these four families, with a further four members who carry the gene mutation but have no clinical evidence of disease. Age at clinical presentation was variable (range 15-68 years) and the mean septal wall thickness was 19.3 +/- 4.6 mm (range 7-33 mm) in clinically affected individuals, including children. In all four families, at least one member had a sudden cardiac death event, including previous cardiac arrest, indicating a more malignant form of HCM. All four mutations disrupted functional interactions with troponin C and T and this may account for the increased severity of disease in these families. CONCLUSIONS: Gene mutations in cTnI occur in Australian families with HCM with a prevalence higher than previously reported and may be associated with a clinically more malignant course, reflecting significant disruptions to troponin complex interactions.

The cryptochrome (cry) gene and a mating isolation mechanism in tephritid fruit flies.

Two sibling species of tephritid fruit fly, Bactrocera tryoni and Bactrocera neohumeralis, are differentiated by their time of mating, which is genetically determined and requires interactions between the endogenous circadian clock and light intensity. The cryptochrome (cry) gene, a light-sensitive component of the circadian clock, was isolated in the two Bactrocera species. The putative amino acid sequence is identical in the two species. In the brain, in situ hybridization showed that cry is expressed in the lateral and dorsal regions of the central brain where PER immunostaining was also observed and in a peripheral cell cluster of the antennal lobes. Levels of cry mRNA were analyzed in whole head, brain, and antennae. In whole head, cry is abundantly and constantly expressed. However, in brain and antennae the transcript cycles in abundance, with higher levels during the day than at night, and cry transcripts are more abundant in the brain and antennae of B. neohumeralis than in that of B. tryoni. Strikingly, these results are duplicated in hybrid lines, generated by rare mating between B. tryoni and B. neohumeralis and then selected on the basis of mating time, suggesting a role for the cry gene in the mating isolation mechanism that differentiates the species.