Familial predisposition to developmental dysplasia of the hip

Developmental dysplasia of the hip (DDH) is a common birth defect and is thought to have genetic contributions to the phenotype. It is likely that DDH is genetically heterogeneous with environmental modifiers. The Utah Population Database (UPDB) is a computerized integration of pedigrees, vital statistics, and medical records representing over 6 million individuals, and is a unique resource providing the ability to search for familial factors beyond the nuclear family, decreasing the effect of a shared environment. The purpose of this study is to assess the degree of relationship between individuals with DDH.

Datasets were created from UPDB statewide birth certificates and from the University of Utah Health Sciences Center enterprise data warehouse using records for DDH and linked to the UPDB. Controls for the dataset were selected that matched cases on birth year and sex and 10 controls were selected per case. Statistics computed for each family were the number of descendants, the observed number of affected, the expected number of affected, P value, familial standardize incidence ratio, relative risks (RRs), and standard error. A kinship analysis tool was used to find pedigrees with excess DDH.

The combined data resulted in 1649 distinct individuals with DDH. RR was significantly increased in first-degree relatives (RR=12.1; P<0.000001), siblings (RR=11.9; P<0.000001) and first cousins (RR=1.7; P=0.04). A total of 468 families were identified with at least 5 affected individuals in a family. These results were then filtered to only contain families that had a P value of less than 0.01. This resulted in 141 founders with anywhere between 4 and 30 affected living descendants with a P value of less than 0.01 with family sizes ranging from 594 to 44,819 descendants. A total of 28 founders had a familial standardize incidence ratio of greater than 5.0.

These data suggest a genetic contribution to DDH with a 12-fold increase in risk for first-degree relatives. Better phenotypic characterization and classification will be critical for future genetic analyses.