Hemihyperplasia, formerly called hemihypertrophy, is a rare disorder in which one side of the body grows more than the other due to an excess production of cells, causing asymmetry. In a normal cell, there is a mechanism that turns off growth once the cell reaches a certain size. However, in hemihyperplasia, the cells on one side aren’t able to stop growing. This causes the affected body area(s) to continue growing or enlarge abnormally. The disorder is congenital, which means that it is evident at birth.
No one is exactly sure what causes hemihyperplasia, but there is some evidence that the disorder runs in families. Genetics seem to play a role, but the genes that seem to cause hemihyperplasia can differ from person to person. A mutation on chromosome 11 is suspected to be associated with hemihyperplasia.
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 others. Also, sometimes the asymmetry or overgrowth of one side can be so slight that it isn’t easily recognizable.
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 noticeable.
Children with hemihyperplasia are at an increased risk for tumors, specifically those that occur in the abdomen. Tumors are abnormal growths that can be benign (noncancerous) or malignant (cancer). In hemihyperplasia, the cells that form a tumor have often lost the ability to stop or “turn off” the growth mechanism. Wilms’ tumor, which is a cancer that occurs in the kidneys, is the most common. Other types of cancerous tumors that are associated with hemihyperplasia are hepatoblastomas (of the liver), adrenocortical carcinomas (of the adrenal gland), and leiomyosarcomas (of the muscle).
A diagnosis is usually made by a physical exam. Symptoms are associated with other conditions, like Beckwith-Wiedemann syndrome (BWS), Proteus syndrome, Russell-Silver syndrome, and Sotos syndrome. Before diagnosing, your health care provider should rule these out. They may also order diagnostic imaging 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 it.
There is no cure for hemihyperplasia. Treatment is centered on screening the patient for tumor growth and treating the tumors. For abnormal limb size, orthopedic treatment and corrective shoes can be recommended.
Next steps after diagnosis
If you think your child has hemihyperplasia or if you have been diagnosed, 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 your doctor on 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.