Name a common autosomal dominant disorder.

Huntington's disease is a well-known example of an autosomal dominant disorder. This type of disorder occurs when only one copy of the mutant gene, inherited from an affected parent, is sufficient to express the condition. In Huntington's disease, the mutation is found in the HTT gene, which leads to the production of an abnormal form of the huntingtin protein, causing progressive neurodegeneration.

Individuals with Huntington's disease typically have a 50% chance of passing the mutated gene to each of their offspring, which is characteristic of autosomal dominant inheritance. The features of this disorder often manifest in mid-adulthood, with symptoms including movement disorders, cognitive decline, and psychiatric issues, which can significantly impact daily living and quality of life.

In contrast, the other conditions listed are associated with different modes of inheritance. Sickle cell disease and cystic fibrosis are examples of autosomal recessive disorders, meaning that an individual must inherit two copies of the mutant gene to exhibit the disease. Phenylketonuria (PKU) is also an autosomal recessive disorder, requiring both alleles to be mutated for the condition to present. Understanding these inheritance patterns helps in genetic counseling and in managing these conditions effectively.