Chapter 3 - Genetic basis of inherited disease

Summary

Inherited disease may be caused at the level of the gene and the chromosome. In principle single gene mutations can lead to genetic diseases which may be distinguished on the basis of five simple modes of inheritance: autosomal dominant, autosomal recessive, X-linked recessive, X-linked dominant, and Y-linked. Myotonic dystrophy, DM1, also known as Steinert disease, is a progressive muscular dystrophy caused by the expansion in number of copies of a CTG repeat in the 3ʹ-untranslated part of the DM1 kinase gene on chromosome 19. Huntington disease is a progressive neuropsychiatric, late-onset disorder. Fragile X syndrome is a form of X-linked mental retardation caused by unstable expansion of a CGG repeat in the 5ʹ untranslated region of the FMR1 gene. Ring chromosomes are formed when genetic material is lost from both ends of a chromosome, creating an unstable situation which is resolved by the fusion of the broken ends.