Perthes disease is a bone disorder, affecting ball and socket joint of the hip.1 It most commonly affects only one hip, but in 10-15% cases, it can affect both the hips. It is a childhood disease that mostly affects children between the age group of 4-8 years and affects boys more than girls in a frequency of 5:1. The synonyms of Perthes disease include Legg Calve Perthes disease, LCPD, Calve Perthes disease and coxaplana.
Perthes disease is characterized by the breakdown or necrosis of the upper end or femoral head of thighbone, which forms the ball in the ball and socket joint of the hip. Necrosis of femoral head is brought about by disruption of blood supply to the head of femur. This necrosis of the head of femur (ball) leads to change in the round shape of the femoral head that incapacitates the free movement of the femur in the hip socket.
This restricted joint movement could lead to symptoms of limited range of motion of the joint, hip pain, limping, cramps and muscle wasting of the affected thigh and hip. It could also lead to referred pain to the knee joint and result and in leg length discrepancy. The remodeling of bone takes place as soon as there is restoration of blood supply to the area. This healing process and reossification takes several years to complete. Osteoarthritis is a very common complication faced by affected children in their adulthood.
Is Perthes Disease Inherited?
The cause of Perthes disease is yet unknown. There have been several studies, which are still ongoing, and there have been no direct correlation to genetic factors. It is most commonly seen in white people with a frequency of 1 to 3 in 20,000 children.
Inheritance refers to a condition that is either hereditary and runs in family. Genetics play an important role in the inheritance of a disease. There can be three classes of diseases based on genetics, namely, strongly genetic, partially genetic and non-genetic diseases. Strongly genetic diseases are inherited, partially genetic diseases are occasionally inherited and non-genetic diseases are not inherited. Previous studies have linked Perthes disease to genetic factors and low birth weight. However, based on newer studies it has been found that Perthes disease is not inherited, although, it did show familial clustering, no major genetic correlation was found. No strong correlation was found between low birth weights also.
In very few cases, there have been mutations in COL2A1 gene that has led to bone deformities resembling that of Perthes disease.2 COL2A1 gene is related to a protein that is responsible in the formation of type II collagen. This type II collagen makes up cartilage (a tough and flexible tissue that forms skeletal structure during early development), which later converts to bone (except cartilage found in nose, ears and forms protective covering of the ends of bones). Type II collagen is necessary for the normal development of bones and connective tissue, which forms the supportive framework of the body.
In Perthes disease, the mutation in COL2A1 gene causes production of an altered protein and the collagen formed from this protein may be abnormal and weak. Necrosis of bone in Perthes disease is related to disruption in blood flow to the head of femur, which is responsible for the bone necrosis. It is still unclear how abnormal type II collagen is related to this or why only hip joint is affected.
When Perthes disease is associated with COL2A1 gene mutation, it is inherited as autosomal dominant pattern. This means only one copy of the altered gene is sufficient to cause this condition. Most of the cases associated with COL2A1 gene mutation are new mutations that have no familial history; these cases are known as sporadic cases. In other, rare cases, this condition is inherited by family (an affected person inherits it from one of the parents) and this is known as familial case.