Basic Genetic Concepts for the Orthopedic Surgeon

Abstract

As a result of scientific advances in genetics understanding of a large number of defects and inherited diseases has been increased including many that involve orthopdic conditions. These disorders in which defects in genetic information are of prime importance are distinguished from those in which a combination of genetic and environmental factors are responsible. Disorders resulting from environmental hazards are not dealt with in this presentation. The focus is on the genetic disorders that are of 3 types - single gene defects chromosomal aberrations and multifactorial traits. Single gene defects are caused by mutant genes and these mutations may be present singly or in a double dose. Discussion focuses on autosomal inheritance sex linkage and irregularities in Mendelian pedigree patterns. Chromosomal aberrations are discussed in terms of numerical and structural aberrations causes of chromosomal aberrations and Downs syndrome. A number of relatively common defects and diseases that are familiar do not fit all the expectations for Mendelian inheritance. These have been shown to be accounted for by multifactorial inheritance of a continuously distributed variable with a developmental threshold separating the continuous distribution into 2 discontinuous segments those showing and those not showing the defect. The characteristic features of the family distribution of certain congenital malformations are presented. Genetic counseling frequently involves the occurrence of a particular disease in a child and the concern of the parents as to whether their future children might be similarly affected. Other areas of concern that lead people to seek genetic counseling are presented along with a discussion of the genetic counseling interview and information pertaining to locating a genetic counselor.