Intrapelvic bulging of the medial acetabular wall.

Mucopolysaccharidosis type IX (MPS9) is a rare progressive lysosomal storage disorder caused by the deficiency of the enzyme hyaluronoglucosaminidase-1, which degrades hyaluronan (summary by Imundo et al., 2011).

Autosomal dominant multiple epiphyseal dysplasia (MED) presents in early childhood, usually with pain in the hips and/or knees after exercise. Affected children complain of fatigue with long-distance walking. Waddling gait may be present. Adult height is either in the lower range of normal or mildly shortened. The limbs are relatively short in comparison to the trunk. Pain and joint deformity progress, resulting in early-onset osteoarthritis, particularly of the large weight-bearing joints.

Autosomal domiant spondyloepiphyseal dysplasia tarda (autosomal dominant SEDT) is an inherited condition that affects bone growth. Signs and symptoms are generally physically apparent by puberty; however, abnormalities may be seen on X-ray at an earlier age. Affected people may have skeletal abnormalities, short stature (with a short neck and trunk, specifically), scoliosis, kyphosis, lumbar hyperlordosis (exaggerated curvature of the lower back), and early-onset progressive osteoarthritis of the hips and knees. Some cases of autosomal dominant SEDT may be caused by changes (mutations) in the COL2A1 gene. As the name suggests, the condition is inherited in an autosomal dominant manner. Treatment is based on the signs and symptoms present in each person and may include surgery and pain management strategies.

Developmental dysplasia of the hip (DDH) is a debilitating condition characterized by incomplete formation of the acetabulum leading to dislocation of the femur, suboptimal joint function, and accelerated wear of the articular cartilage, resulting in arthritis. Undetected hip dysplasia is the leading cause of osteoarthritis of the hip in young individuals, causing over 40% of cases in that age group (summary by Feldman et al., 2013). For discussion of genetic heterogeneity of developmental dysplasia of the hip, see DDH1 (142700).

Avascular necrosis of the femoral head (ANFH) is a debilitating disease that usually leads to destruction of the hip joint in the third to fifth decade of life. The disorder is characterized by progressive pain in the groin, mechanical failure of the subchondral bone, and degeneration of the hip joint. Nearly one-half of patients require hip replacement before 40 years of age. ANFH represents a specific form of the broader disease category of osteonecrosis (summary by Mont and Hungerford, 1995). Genetic Heterogeneity of Primary Avascular Necrosis of the Femoral Head ANFH2 is caused by mutation in the TRPV4 gene (605427) on chromosome 12q24. Mutation in COL2A1 has also been found in Legg-Calves-Perthes disease (LCPD; 150600), a form of ANFH in growing children.

Inclusion body myopathy associated with Paget disease of bone (PDB) and/or frontotemporal dementia (IBMPFD) is characterized by adult-onset proximal and distal muscle weakness (clinically resembling a limb-girdle muscular dystrophy syndrome), early-onset PDB, and premature frontotemporal dementia (FTD). Muscle weakness progresses to involve other limb and respiratory muscles. PDB involves focal areas of increased bone turnover that typically lead to spine and/or hip pain and localized enlargement and deformity of the long bones; pathologic fractures occur on occasion. Early stages of FTD are characterized by dysnomia, dyscalculia, comprehension deficits, and paraphasic errors, with minimal impairment of episodic memory; later stages are characterized by inability to speak, auditory comprehension deficits for even one-step commands, alexia, and agraphia. Mean age at diagnosis for muscle disease and PDB is 42 years; for FTD, 56 years. Dilated cardiomyopathy, amyotrophic lateral sclerosis, and Parkinson disease are now known to be part of the spectrum of findings associated with IBMPFD.