Molecular Diagnostics of Genetic Diseases: Experience from Studies of DMD, APC, TSC1, and OPG Genes. Part 1.

Abstract

Over the past decade geneticists have searched for rapid and efficient means of identification of genetic diseases. Nucleic acid techniques, such as restriction fragment length polymorphisms, polymerase chain reaction, and sequence analysis of amplified DNA are making increasing inroads as tools in diagnostic laboratories. Our laboratory is involved in the molecular diagnostics of several genetic diseases including Duchenne muscular dystrophy, familial adenomatous polyposis coli, tuberous sclerosis, and osteoporosis. Each disease varies in type of molecular lesions and different approaches are applied to achieve the best mutation detection rate. Duchenne/Becker muscular dystrophy (DMD/ BMD) is a lethal X-linked recessive disease caused by mutations within the dystrophin gene (DMD gene). The DMD gene is the largest known human gene, spanning about 2,500kb and consisting of 79 exons. In approximately 60% of DMD/BMD patients, deletions of one or more exons are detected. Carrier detection still causes problems for many cases, because of the enormous size of the DMD gene and the high intragenic recombination frequency. Familial adenomatous polyposis coli (FAP) is a dominantly inherited autosomal disorder caused by germ line mutation in the adenomatous polyposis coli (APC) gene and is characterized by early onset of multiple adenomatous polyps, which leads to the development of colorectal carcinoma. The development of colon carcinoma is associated with loss of heterozygosity (LOH) in the APC gene and accumulation of mutations in a number of tumor suppressor genes. Detection of mutation carriers in FAP families before pathological symptoms occur is very important and makes possible clinical treatment. Molecular changes in the APC gene were found in 30% of the studied patients with familial adenomatous polyposis coli, with a similar frequency for the common delta 1309 mutation as in other populations. In a Polish population of FAP patients, most mutations were localized in a region of the APC gene encompassing codons 1040-1309.