Genetic aspects of orthopedic conditions.

Genetic conditions seen by orthopedists may be divided into Mendelian disorders, chromosome abnormalities and multifactorial conditions. Mendelian disorders involve the abnormality of a single gene and obey the rules of Mendelian inheritance. Chromosome abnormalities are caused by the absence or duplication of a sufficient number of genes to allow this abnormality to be detected by chromosome studies. Chromosome studies are used to confirm the diagnosis of well described syndromes of deletion or trisomy. These studies are also necessary to determine whether mongolism has been caused by non-disjunction or translocation, so that proper genetic counseling can be carried out in these conditions. Multifactorial conditions are determined by several genes or more commonly, by a combination of genetic and environmental factors. These conditions recur in families in a greater incidence than one would expect in the general population but do not obey the rules of Mendelian inheritance. Genetic counseling cannot be performed without an absolute diagnosis, an absolute knowledge of the patterns of inheritance and a well documented family pedigree. The basic principles of genetics covered in this article should allow the orthopedist to understand when genetic counseling is indicated for his patients.