May experience menstrual irregularities, including early onset of menopause. Occurs in females, but symptoms are less severe. Passes from symptomless male carrier to grandson. Punnett square provides phenotypic ratio if all sperm are given equal chance to fertilize all eggs. This is an autosomal dominant disorder that affects one in 3,000 people.
Affected individuals have tan skin spots at birth, which develop into benign tumors.
Neurofibromas are comprised of nerve cells or other cell types. It is a tumor-suppressor gene active in controlling cell division. This is also an autosomal dominant disorder that affects one in 20,000 people. It leads to progressive degeneration of brain cells, which in turn causes severe muscle spasm, personality disorders, and death in 1015 years from onset. The gene for Huntington disease is located on chromosome 4.