Hemihyperplasia, formerly called hemihypertrophy, is a rare disorder in which one side of the body grows more than other, causing asymmetry. In a normal cell, there is a mechanism that turns off growth once the cell reaches a certain size. However, in hemihypertrophy, the cells on one side aren’t able to stop growing. This causes the body to continue growing or enlarge abnormally. This disorder is congenital, which means that it is evident at birth.
No one is sure what causes hemihyperplasia, but there is some evidence that this disease runs in families. Genetics seems to play a role, but the genes that seem to cause hemihyperplasia can differ from person to person. A mutation on gene 11 is suspected to be the cause.
Statistics vary on how many people actually have this disorder. There are several reasons for this. First, the symptoms of hemihyperplasia are similar to other diseases, so sometimes the diagnosis can be confused with other diseases. Also, sometimes the asymmetry or overgrowth of one side can be so slight that it isn’t easily recognizable. Hemihyperplasia affects approximately 1 in 13,200 births, though other research indicates about 1 in 86,000 births (Beck, 1968, Parker 1969).
The most obvious symptom of hemihyperplasia is the tendency for one side of the body to be larger than the other side. An arm or a leg can be longer or larger in circumference. In some cases, the trunk or the face on one side is larger. Sometimes this isn’t really noticeable unless the individual lies on a bed or flat surface (called the bed test). In other cases the difference in posture and gait (how someone walks) is very obvious.
Children with hemihyperplasia are at an increased risk for tumors, specifically those that occur in the abdomen. Wilms tumors, which occur in the kidneys, are the most common. Tumors are an abnormal cancerous growth that can be benign (harmless) or malignant (harmful). Like hemihyperplasia, the cells that form a tumor have often lost the ability to stop or “turn off” the growth mechanism. Other types of tumors that are associated with hemihyperplasmia are hepatoblastomas (tumor of the liver), adrenal cell carcinomas, and leiomyosarcomas (tumor of the muscle tissue).
A diagnosis is usually made by a physical exam. Symptoms of this disease are associated with other diseases, like Beckwith-Wiedemann syndrome (BWS), Proteus syndrome, Russell-Silver syndrome, and Sotos syndrome. Before diagnosing, your health care provider should rule out these diseases. They may also order radiologic exams to screen for tumors.
Because this disorder is rare and often overlooked, it is recommended that the diagnosis be made by a clinical geneticist who is familiar with the syndrome.
There is no cure for this disorder. Treatment is centered on screening the patient for tumor growth and treating the tumors. For abnormal limbs size, orthopedic treatment and corrective shoes can be recommended.
If you think your child has hemihyperplasia or if you have a diagnosis, you should also consider the following:
- Get a referral to a clinical geneticist for evaluation.
- Know your doctor’s plan for tumor surveillance. Some guidelines recommend screening for tumors for the first six years. Others recommend abdominal ultrasounds every three months until the age of 7.
- Consult the doctor in whether a serum alpha-fetoprotein (SAF) measurement should be taken. Some guidelines recommend that the SAF level be measured every three months until the age of 4. In some cases, the SAF, a type of protein, is very high in infants with hemihyperplasia.
If your child is diagnosed with hemihyperplasia, it is a good idea to regularly perform an abdominal examination of your child. Ask your doctor for recommendations on how to do this. Parental involvement in treatment has shown to be effective in some cases.