Brachydactyly type A1

Patient 1 has Brachydactyly type A1, which causes the middle fingers of fingers and toes to be reduced or absent. Short stature and malformed epiphyses is also common in patients with this disease. Brachydactyly type A1 is usually caused by a mutation on the BDA1B gene or on the IHH (Indian Hedgehog gene). It is inherited in an autosomal dominant fashion. While there are different types of mutations on BDA1B or IHH that can lead to the disease, missense mutations on IHH are a common pathological cause. The mutant Hedgehog protein encoded by IHH is unable to bind to a receptor called Patched-1, which is responsible for differentiation. This mutation along with others on BDA1 and IHH have the potential to prevent cellular growth, condensation and differentiation, which can lead to abnormal bone development.