PIK3CA-Related Segmental Overgrowth

In: GeneReviews® [Internet]. Seattle (WA): University of Washington, Seattle; 1993–2020.


Clinical characteristics: PIK3CA-associated segmental overgrowth includes disorders of brain (e.g., MCAP [megalencephaly-capillary malformation] syndrome, hemimegalencephaly); and segmental body overgrowth (e.g., CLOVES [congenital lipomatous asymmetric overgrowth of the trunk, lymphatic, capillary, venous, and combined-type vascular malformations, epidermal nevi, skeletal and spinal anomalies] syndrome, fibroadipose hyperplasia [FH]). Heterozygous (usually somatic mosaic) pathogenic variants of PIK3CA are causative.

MCAP syndrome is characterized by the major findings of (1) megalencephaly (MEG) or hemimegalencephaly (HMEG) associated with neurologic findings of hypotonia, seizures, and mild to severe intellectual disability; and (2) cutaneous capillary malformations with focal or generalized somatic overgrowth. Additional findings can include digital anomalies (syndactyly, polydactyly), cortical malformations – most distinctively polymicrogyria (PMG); and variable connective tissue dysplasia.

CLOVES (or CLOVE) syndrome and fibroadipose hyperplasia (FH) may be associated with (1) MEG or HMEG; and (2) patchy segmental overgrowth associated with skeletal anomalies, lipomatosis, vascular malformations, and epidermal nevi.

Diagnosis/testing: PIK3CA-associated segmental overgrowth is confirmed in an individual with a pathogenic variant on one PIK3CA allele, typically in affected tissues. Because the vast majority of PIK3CA pathogenic variants arise postzygotic (and are thus mosaic), more than one tissue may need to be tested. Failure to detect a PIK3CA pathogenic variant does not exclude a clinical diagnosis of the PIK3CA-associated segmental overgrowth disorders in individuals with suggestive features.

Management: Treatment of manifestations: Significant or lipomatous segmental overgrowth may require debulking; scoliosis and leg-length discrepancy may require orthopedic care and surgical intervention. Neurologic complications (e.g., obstructive hydrocephalus, increased intracranial pressure, progressive and/or symptomatic cerebellar tonsillar ectopia or Chiari malformation; epilepsy in those with HMEG) may warrant neurosurgical intervention. Routine treatment of the following, when present, is indicated: cardiac and renal abnormalities; intellectual disabilities and behavior problems; motor difficulties; speech, swallowing, and feeding difficulties.


  1. MCAP syndrome: Follow up no less than every six months until age six years and at least yearly thereafter to monitor for neurosurgical complications, breathing or sleep disorders, seizures and orthopedic complications. Provisionally recommended imaging in early childhood includes brain MRI every six months for the first two years, then yearly until age eight years for neurologic complications (e.g., hydrocephalus, cerebellar tonsillar ectopia). Consider screening for Wilms tumor following the protocol suggested for Beckwith-Wiedemann syndrome (BWS) (by ultrasound examination every 3 months until age 8 years); however, tumor risk in PIK3CA-related segmental overgrowth is undetermined and appears to be lower than in BWS.

  2. CLOVES syndrome and FH: Monitoring for severe scoliosis, infiltrative lipomatous overgrowth, paraspinal high-flow lesions with spinal cord ischemia, lymphatic malformations, cutaneous vesicles, orthopedic problems, central phlebectasias, and thromboembolism.

Genetic counseling: PIK3CA-associated segmental overgrowth is not typically inherited. Most affected individuals with MCAP reported to date (21/24) had somatic mosaicism for pathogenic variants in PIK3CA, suggesting that mutation occurred post-fertilization in one cell of the multicellular embryo. Two of 24 affected individuals had a de novo germline pathogenic variant in PIK3CA. All reported individuals with CLOVES and FH had somatic mosaicism for pathogenic variants in PIK3CA. No confirmed instances of vertical transmission or sib recurrence have been reported. Because family members are not known to have an increased risk, prenatal diagnosis is usually not indicated for family members.

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