[Hypertrophic cardiomyopathy: practical application of genetic research]

Hypertrophic cardiomyopathy is usually familial with an autosomal dominant mode of transmission. The condition is genetically heterogeneous. The first defective gene to be described was that of the beta heavy chain of cardiac myosin (beta-MHC, chromosome 14 q11-q12) where over 20 different localised false sense mutations and a hot point of mutation in exon 13 have been reported. This locus seems to be implicated in 30% of families studied. Systematic screening of the genome has led to the detection of new sites on chromosomes 1, 11 and 15. No gene has yet been identified in these three new loci. For all new families, present strategy consists in determining the locus responsible for the disease by linkage analysis. For beta-MHC locus a panel of several markers (the two MYO I and MYO II microsatellites of the beta-MHC gene and two new AFN microsatellites) has been established which allows accurate detection of whether the haplotype cosegregates with the disease, even in relatively small families. It is then necessary to define the mutation by PCR amplification of the exons followed by electrophoresis on Hydrolink-MDE gels and sequencing of the mutant exons. Some subjects are genotypically affected but phenotypically normal and it seems the penetrance varies with the type of mutation. Analysis of the genotype/phenotype relationship should be continued in order to improve our knowledge of the consequences of each mutation. The genotype diagnosis is therefore complex and cannot be undertaken at present of the examination of the propositus. Whole families must be sampled.(ABSTRACT TRUNCATED AT 250 WORDS)