Discovering the Gene(s) Causing Developmental Dysplasia of the Hip (RP#2)

Developmental dysplasia of the hip (DDH), formerly known as Congenital Dislocation of the Hip (CDH) is a relatively common disorder that can lead to early onset arthritis of the hip. It is believed that DDH is the major cause of arthritis of the hip in young patients. The majority of patients with DDH are unaware of their condition. Only a very small number of these patients with the extremely severe form of the disease (dislocated hip) are identified at birth. The remaining patients usually seek help when severe arthritis is present and joint preservation treatment is not possible. The exact etiology of this condition remains elusive. Based on reports in the literature, DDH is believed to have a genetic basis.

Dr. Javad Parvizi at Rothman Institute (RT) in Philadelphia has extensive experience with this condition because their center provides joint preservation procedures such as pelvic and femoral osteotomy. They also have extensive experience with hip replacement in these patients. They are aware of some families with many affected individuals. Close history taking and examination of these patients has suggested that there may indeed be a genetic basis for DDH. Based on our findings so far, we believe that a dominant pattern of inheritance may exist, implying that this disorder may be inherited in a Mendelian manner (Single gene disorder).

Furthermore, Dr. Parvizi's group have documented a peculiar pattern of dominant inheritance in which all affected males give rise to only affected female children, suggesting that the disorder may be inherited as an X-linked dominant trait. X-linked dominant is the mode of inheritance in which a gene on the X chromosome is dominant. The X-linked dominant inheritance may in part account for the large number of females affected with the trait. Understanding the inheritance mechanism of this disease will allow better genetic counseling and monitoring of affected individuals and their families.

The reason behind this study is to investigate the possible genetic inheritance of the disease. Knowing this information will allow us to test patients for the disease early and before arthritis develops. In addition it is possible that better treatments may be designed based on this knowledge.

DDH is a relatively common condition. Although the most severe form of DDH is usually diagnosed during birth (dislocated hip), the majority (>80%) of patients with this condition do not even know that they suffer from this disease and usually discover their condition when disabling arthritis of the hip develops in early adulthood.