Thompson & Thompson Genetics in Medicine

Human Genome Project

Efforts to catalogue all human genes, understand their structure and regulation, determine the extent of variation in these genes in different populations, and uncover how genetic variation contributes to disease.

Genomic Medicine

Large-scale analysis of the human genome and its products, including the control of gene expression, human gene variation, and interactions between genes and the environment, to medical care.

Chromosome Disorders

Mistake due to excess or a deficiency of the genes located on entire chromosomes or chromosome segments. Common, affecting approximately 7 per 1000 liveborn infants and accounting for approximately half of all spontaneous abortions occurring in the first trimester of pregnancy.

Single-Gene Defects

Caused by pathogenic mutations in individual genes. The mutation may be present on both chromosomes of a pair (one of paternal origin and one of maternal origin) or on only one chromosome of a pair (matched with a normal copy of that gene on the other copy of that chromosome). These defects often cause diseases that follow one of the classic inheritance patterns in families (autosomal recessive, autosomal dominant, or X-linked). The mutation may be in the mitochondrial rather than in the nuclear genome in a few cases. Usually rare with a frequency that may be as high as 1 in 500 to 1000 individuals. The incidence of serious single-gene disorders in the pediatric population has been estimated to be approximately 1 per 300 liveborn infants; over an entire lifetime, the prevalence of single-gene disorders is 1 in 50.

Multifactorial Disease with Complex Inheritance

The majority of diseases in which there is a genetic contribution, as evidenced by increased risk for disease (compared to the general public) in identical twins or close relatives of affected individuals, and yet the family history does not fit the inheritance patterns seen typically in single-gene defects. There appears to be no single error in the genetic information in many of these conditions. The disease is the result of the combined impact of variant forms of many different genes; each variant may cause, protect from, or predispose to a serious defect, often in concert with or triggered by environmental factors. Estimates of the impact of multifactorial disease range from 5% in the pediatric population to more than 60% in the entire population.