Brachydactyly type A1

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The IHH gene at 2q35 codes for the 411 amino acid peptide indian hedgehog protein with autoproteolysis and cholesterol transferase activity which is further processed into:

  1. Indian hedgehog protein N-product
    • Active species in both local and long-range signalling
    • N-palmitoylation is required for full activity
  2. Indian hedgehog protein C-product
    • No signalling activity
    • Diffuses from the cell

It is essential for a variety of patterning events during development and endochondral ossification. It induces parathyroid hormone-related protein. The defective IHH gene can cause:

  • Brachydactyly type A1 (BDA1)
    • Autosomal dominant disorder with middle phalanges rudimentary or fused with the terminal phalanges. The proximal phalanges of the thumbs and big toes are short.
  • Acrocapitofemoral dysplasia (ACFD)
    • Short stature of variable severity. Cone-shaped epiphyses or similar epiphyseal configuration with premature epimetaphyseal fusion results in shortened skeletal components.
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