Patella Aplasia-Hypoplasia

Clinical Features

Aplasia or hypoplasia of the patella, except as a feature of the nail-patella syndrome (NPS; 161200), is rare. Familial occurrence was reported by Bernhang and Levine (1973) and by Kiss et al. (1977). Braun (1978) reported a father with bilateral absence and son with pronounced hypoplasia.

Mapping

Mangino et al. (1999) investigated a 4-generation family segregating an autosomal dominant, isolated PTLAH. By genomewide scanning, they localized the gene responsible for this defect to 17q21-q22. Multipoint analysis gave a maximum lod score of 3.39, with a most likely location for the PTLAH locus between D17S787 and D17S1604.

Molecular Genetics

In a family segregating PTLAH mapping to 17q21-q22, Mangino et al. (1999) sequenced the Noggin gene (NOG; 602991) and found no mutations in affected subjects.

Bongers et al. (2004) stated that mutations in the TBX4 gene (601719), which cause the small patella syndrome (147891), are unlikely to cause PTLAH because the gene maps outside the critical region for PTLAH. They found no mutations in the TBX4 gene in a family with PTLAH, but could not exclude disruption of long-range TBX4 regulatory elements as a cause of the disorder.

Heterogeneity

Bongers et al. (2002) described a family with isolated patella aplasia-hypoplasia in 3 generations in which linkage to the nail-patella syndrome locus on 9q34 and the PTLAH locus on 17q was excluded. The proband, aged 28 years, had bilateral small patellae and had complained of instability and dislocation of the patellae since the age of 7 years. Surgery for patellar dislocation was performed at ages 13 and 14 years. There were no iliac horns or other skeletal features of NPS. Her father and paternal grandmother had patellar anomalies on physical examination. In addition to PTLAH, the proband and her father had hereditary motor and sensory neuropathy, type 1A, or CMT1A (118220), due to duplication of the PMP22 gene (601097) on 17p. The paternal grandmother had no clinical characteristics of CMT and normal PMP22 status was established.