Which type of inheritance does Vitamin D-resistant rickets fall into?

• A. X-linked dominant
• B. X-linked recessive
• C. Autosomal dominant
• D. Autosomal recessive

Answer: (A)

Vitamin D-resistant rickets is classified as X-linked dominant inheritance. This condition arises from mutations in the gene responsible for the production of a protein that is critical for regulating phosphate levels in the body, which is essential for bone mineralization. The fact that it is X-linked means that the gene is located on the X chromosome, and because it is dominant, only one copy of the mutated gene is sufficient to cause the disorder.

In X-linked dominant disorders, affected males can pass the condition to all of their daughters but not their sons, because males have only one X chromosome. Affected females can pass the condition to both their daughters and sons, which is a unique characteristic of X-linked dominant inheritance. This pattern fits well with Vitamin D-resistant rickets, as it often displays traits consistent with this mode of inheritance, leading to characteristic symptoms in those affected.

Understanding the way inheritance works in this context helps clarify the broader implications for genetic counseling and the potential for passing on the condition within families.