반성유전 질환

Some inherited disorders are caused by mutations to a single gene. And when located on a sex chromosome, the disorder is said to be sex-linked. Depending on which sex chromosome the gene is located on and whether one or both copies are required for proper function, these disorders are considered either Y-linked, X-linked dominant or X-linked recessive.

First, Y-linked disorders such as Y chromosome infertility are caused by mutations on genes located on the Y chromosome and can only be passed down from father to son. Second, X-linked dominant disorders including Fragile X syndrome require only one copy of the mutated gene, affect both females and males and cannot be passed from fathers to sons. Lastly, X-linked recessive disorders affect males much more often because females need two copies of the mutated gene.

Yet, unaffected heterozygous women can be carriers and have a 50% chance to pass it on to their sons. For example, an X-linked recessive disorder called Duchenne Muscular Dystrophy or DMD almost exclusively affect boys. DMD is caused by mutations in the gene encoding dystrophin, a protein involved in the proper contraction and repair of skeletal and cardiac muscle cells. These mutations can lead to structural or functional changes to the dystrophin protein without which muscle cells weaken and eventually atrophy.