Torticollis in an infant caused by hereditary muscle aplasia.

Torticollis is a common condition presenting to the general or pediatric orthopedist. We describe the case of a child with severe torticollis caused by a hereditary unilateral absence of the sternocleidomastoid and trapezius muscles. Both his father and paternal grandfather had a forme fruste, with similar but milder findings. Electromyography and cross-sectional imaging were valuable in making the diagnosis. We believe this is the first reported case of hereditary unilateral muscle aplasia presenting as torticollis in an infant.