Segmental overgrowth describes a condition where there is an excess of growth in different parts of the body, but normal growth elsewhere.

Examples of segmental overgrowth conditions include:

  • PIK3CA related overgrowth spectrum (PROS)

Within the PROS category we see the following conditions:

 Hemihyperplasia multiple lipomatosis (HHML)


 Fibroadipose overgrowth (FA0)

 Muscle hemihypertrophy

 Facial Infilitrating lipomatosis

Congenital  lipomatous overgrowth, vascular malformations, epidermal  naevi and skeletal abnormalities (CLOVES)

 Megalencephaly-capillary malformation (MCAP)

Skin disorders: Epidermal Nevi, Seborrheic keratose, Benign lichenoid keratoses

Klippel-Trenauney Syndrome (KTS)

What causes segmental overgrowth?

The underlying cause of many of these conditions are genetic changes in the genes important for controlling growth e.g PIK3CA, PIK3R2, AKT1, AKT3 and mTOR. The gene changes are not inherited or passed on to children, and are only found in the parts of the body that are affected by the overgrowth.

What kind of problems do patients with segmental overgrowth have?

Patients may have overgrowth of any part of their body. This could be an enlarged toe, finger, arm or leg, or more extensive overgrowth affecting both legs, the brain or one side of the the body. Tissues in the body affected my include fat, muscle, bone, blood vessels, skin and nerves. For most patients, overgrowth is present at birth or develops in early childhood and for some the growth will slow down or stop in early adulthood, but for others the growth may carry on into adult life.

What treatments are available?

Surgery is the only available treatment at present. In the future, it is possible that tablets could become available to help slow the growth. These tablets are currently under investigation in a laboratory setting, with plans for clinical trials in the next few years.

How do I get myself or child tested?

To get tested for these gene changes, doctors will need to look at genes in the affected tissue and this may involve taking a small skin biopsy. You can speak to your local doctor about getting tested, or alternatively contact a research group with a special interest in segmental overgrowth, see contact details in the other support group tab