A pattern of Mendelian inheritance whereby an affected individual possesses one copy of a mutant allele and one normal allele. (In contrast, recessive diseases require that the individual have two copies of the mutant allele.) Individuals with autosomal dominant diseases have a 50-50 chance of passing the mutant allele and hence the disorder onto their children. Examples of autosomal dominant diseases include Huntington's disease, neurofibromatosis, and polycystic kidney disease.
An autosomal dominant gene is one that occurs on an autosomal (non-sex determining) chromosome. As it is dominant, the phenotype it gives will be expressed even if the gene is heterozygous. This contrasts with recessive genes, which need to be homozygous to be expressed.
The chances of an autosomal dominant disorder being inherited are 50% if one parent is heterozygous for the mutant gene and the other is homozygous for the normal, or wild type gene. This is because the offspring will always inherit a normal gene from the parent carrying the wild-type genes, and will have a 50% chance of inheriting the mutant gene from the other parent. If the mutant gene is inherited, the offspring will be heterozygous for the mutant gene, and will suffer from the disorder. If the parent with the disorder is homozygous for the gene, the offspring produced from mating with an unaffected parent will always have the disorder. See Mendelian inheritance.
The term vertical transmission refers to the concept that autosomal dominant disorders are inherited through generations. This is obvious when you examine the pedigree chart of a family for a particular trait. Because males and females are equally affected, they are equally likely to have affected children.
Although the mutated gene should be present in successive generations in which there are more than one or two offspring, it may appear that a generation is skipped if there is reduced penetrance.
Examples of dominant genes include the tumor supressor genes BRCA1 and BRCA2. Mutations in these genes lead to the development of breast cancer, as the tumor-suppressing functions of the proteins encoded by the genes have been disabled.
Another example of an autosomal dominant disorder is Huntington's disease, which is a neurological disorder resulting in impaired motor function. The mutant gene results in an abnormal protein, containing large repeats of amino acid glutamine. This defective protein is toxic to neural tissue, resulting in the characteristic symptoms of the disease.
Other forms of inheritance are: autosomal recessive, X-linked and mitochondrial.