X-linked recessive diseases are genetic disorders caused by mutations on the X chromosome. Males (who have only one X chromosome) are more frequently affected by X-linked recessive conditions than females. Affected males typically do not transmit the disorder to their sons (who inherit their Y chromosome) but do transmit the gene mutation to their daughters (who inherit their X chromosome).
Here are some of the most common X-linked recessive diseases:
- Fragile X: Fragile X syndrome is a genetic condition that causes a range of developmental problems including learning disabilities and cognitive impairment. Usually, males are more severely affected by this disorder than females.
- Duchenne Muscular Dystrophy (DMD) and Becker Muscular Dystrophy: These are both caused by mutations in the dystrophin gene. DMD is more severe than Becker, with symptoms appearing in early childhood and progressing rapidly.
- Hemophilia A and Hemophilia B:
- Hemophilia A is caused by a deficiency of factor VIII.
- Hemophilia B (also known as Christmas disease) is due to a deficiency of factor IX. Both conditions result in impaired blood clotting, leading to prolonged bleeding and easy bruising.
- Color Blindness (Red-Green): This is the inability to distinguish between certain shades of red and green. It’s caused by mutations in the genes encoding the red or green photopigments in the retina.
- Glucose-6-phosphate Dehydrogenase (G6PD) Deficiency: Affected individuals may have episodes of hemolysis (breakdown of red blood cells) when exposed to certain triggers like fava beans, certain infections, or specific medications.
It’s important to note that while these diseases are X-linked recessive, some female carriers can manifest milder symptoms or have clinical findings related to the disease, especially if there’s unfavorable X-inactivation (also called lyonization) in their cells. Genetic counseling is beneficial for families with a history of X-linked recessive diseases.