FIG. 2. Increasing alanine repeats and decreasing dosage of Hox genes cause similar defects. Top panel from left to right shows hands from: a patient with a +7 alanine expansion and syndactyly of fingers III/IV, the mildest form of SPD, a patient with a +10 alanine expansion showing the full clinical picture with syndactyly III/IV (surgically removed) and polydactyly in the syndactylous web, mother of this patient with a homozygous +10 alanine expansion showing severe brachydactyly, syndactyly of fingers III/IV and oligodactyly of feet. Bottom panel shows dose dependent variation of dactyly in feet of mice with varying Hox genotypes. Genes from the Hoxd and Hoxa clusters were inactivated as schematized below with the genes whose functions were removed in black. The progressive inactivation goes together with a transition from pentadactyly (left) to polydactyly (middle) to oligodactly (right). From Zakany et al (1997), with permission.

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