Rare and isolated. During the early weeks of pregnancy, the child’s fingers and toes form in a “mitten” of skin. By the end of the second month of pregnancy, the extra skin dissolves, and the fingers and toes should separate. Syndactyly occurs when the fingers and toes do not fully separate during development. Some forms of syndactyly are inherited, while others are sporadic, . Most cases of syndactyly are isolated.