Based on HLA typing, what is the probability of their children developing ankylosing spondylitis?

The probability of children developing ankylosing spondylitis (AS) based on HLA typing is primarily influenced by the presence of the HLA-B27 antigen, which is strongly associated with the disease. When one parent is HLA-B27 positive, the risk for their children to inherit this allele increases significantly.

If one parent is HLA-B27 positive, there is typically a 50% probability that each child will inherit the HLA-B27 allele from that parent. While inheriting the allele increases the likelihood of developing ankylosing spondylitis, it does not guarantee that the child will develop the disease, as environmental factors and additional genetic components also play significant roles in disease manifestation.

In contrast, if both parents were HLA-B27 positive, the probability could be higher, but that isn't specified in this question. The question focuses on the scenario with one HLA-B27 positive parent, which supports the idea that the probability of their children developing AS is around 50%, as they have a 50% chance to inherit the allele from the affected parent.

This interpretation aligns with the genetic principles of inheritance and the specific associations of HLA-B27 with ankylosing spondylitis, making 50%