A report of two cases of familial occipitalization of the atlas in a father and his daughter.

Occipitalization of the atlas (OA) (atlantooccipital assimilation) is a rare congenital anomaly that results in fusion of the C0-C1 complex. Here, we report the two cases of familial OA occurring in a father and his daughter and describe the pathologic features of this rare developmental anomaly. A 70-year-old father and his 30-year-old daughter seeking conservative care for musculoskeletal complaints presented to a chiropractic clinic. Radiographs of the cervical spine demonstrated OA. This represents a novel example of this anomaly in two patients with a direct familial relationship.