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A polymalfomative syndrome characterized by cutaneous capillary malformations, megalencephaly, cortical brain malformations (most distinctively polymicrogyria), abnormalities of somatic growth with body and brain asymmetry, developmental delay, and characteristic facial dysmorphism.
Features include very common findings: Wide mouth, Macrocephaly, Facial asymmetry, and Nevus flammeus and others; and common findings: Low muscle tone (hypotonia), Hydrocephalus, Enlarged brain ventricles (ventriculomegaly), and Intellectual disability and others. 55 total HPO annotations.
Organ System | Phenotype Count | Example Features |
|---|---|---|
Brain and nerves | 7 | Seizure, Hydrocephalus, Enlarged brain ventricles (ventriculomegaly) |
Arms and legs | 4 | Hand polydactyly, Toe syndactyly, Foot polydactyly |
Muscles | 3 | Low muscle tone (hypotonia), Generalized hypotonia, Damage to the optic nerve (optic atrophy) |
Head and neck | 3 | Progressive macrocephaly, Macrocephaly, Facial asymmetry |
Heart and blood vessels | 2 | Ventricular septal defect, Arrhythmia |
Growth and development | 2 | Asymmetric growth, Failure to thrive |
Bones and joints | 1 | Joint hypermobility |
Kidneys and urinary system | 1 | Nephroblastoma |
Skin | 1 | Visible small blood vessels on skin (telangiectasia of the skin) |
Reproductive system | 1 | Abnormal nervous system morphology |
Eyes | 1 | Damage to the optic nerve (optic atrophy) |
Neoplasm | 1 | Neoplasm |
PIK3CA-related overgrowth spectrum (PROS) includes overgrowth of a broad range of tissues that may or may not be accompanied by cellular dysplasia. Prior to the understanding of the molecular nature of PROS, a number of distinct but overlapping phenotypes were clinically described and given names . In general, PROS can be divided into an isolated form (when a person has a focal lesion that affects only one tissue or body part; see ) and a syndromic form (i.e., overgrowth plus at least two other features in two systems; see ). A targeted therapy aimed at inhibiting PI3K-related pathway overgrowth has been approved by the FDA . Table 2. Selected Isolated PIK3CA-Related Overgrowth Phenotypes by Affected Organ or Tissue
Organ or Tissue | Phenotype | Comment |
|---|---|---|
Brain/Head | HMEG: brain overgrowth affecting 1 hemisphere w/or w/o cortical dysplasia | Cognitive developmental disabilities; Seizures are common.; Focal neurologic deficits may be present.; May result in facial asymmetry Focal cortical dysplasia1 |
PIK3CA function has not been fully characterized.
Megalencephaly-capillary malformation-polymicrogyria syndrome is associated with mutations in the PIK3CA gene on chromosome 3.
PIK3CA-related overgrowth spectrum (PROS) encompasses a range of clinical findings in which the core features are congenital or early-childhood onset of segmental/focal overgrowth with or without cellular dysplasia in the absence of a family history of similarly affected individuals (i.e., single occurrence in a family). Prior to the identification of PIK3CA as the causative gene, PROS was separated into distinct clinical syndromes based on the tissues and/or organs involved .
PROS should be considered in individuals with the following clinical, brain MRI, and family history findings .
Clinical features
Source: GeneReviews — "PIK3CA-Related Overgrowth Spectrum"
A number of overgrowth and megalencephaly disorders overlap with the PIK3CA-related overgrowth spectrum (PROS), including those summarized in . Table 4. Genes of Interest in the Differential Diagnosis of PIK3CA-Related Overgrowth Spectrum (PROS)
Gene(s) | Disorder | MOI | Clinical Features of Disorder |
|---|---|---|---|
Proteus syndrome | NA (somatic) | Focal somatic overgrowth, epidermal nevi, vascular malformations, dysplastic adipose tissue | Cerebriform connective tissue nevi postnatal onset of overgrowth (vs congenital onset in PROS). Absence of characteristic truncal fatty-vascular mass, spinal paraspinal fast-flow lesions, acral abnormalities of CLOVES syndrome AKT3 CCND2 PIK3R2 |
Genetic testing for PIK3CA is available. Testing is considered confirmatory for diagnosis.
No approved treatments are currently available for megalencephaly-capillary malformation-polymicrogyria syndrome. The disease remains an area of unmet medical need.
Clinical practice guidelines for PIK3CA-related overgrowth spectrum have been published (full text). Additionally, a targeted pharmacologic therapy has been FDA approved .
To establish the extent of disease and needs in an individual with PIK3CA-related overgrowth spectrum (PROS), the evaluations summarized (if not performed as part of the evaluation that led to the diagnosis) are recommended. Note: Assessment is complicated by variable findings in individuals with this condition. Accurate and thorough assessment of medical history is necessary to evaluate for vascular malformations as well as other clinical features.
Table 5.
Recommended Evaluations Following Initial Diagnosis in Individuals with PIK3CA-Related Overgrowth Spectrum
System/Concern | Evaluation | Comment
Constitutional
(overgrowth) | Measure growth parameters incl head circumference, total body length, length of arms, hands, legs feet. | To assess for generalized segmental overgrowth (incl leg length discrepancy) macrocephaly
Consider whole-body MRI. | In those w/truncal overgrowth
Consider limb radiographs subsequent limb MRI. | In those w/segmental or generalized overgrowth of a limb
Consider spinal ultrasound in infants spinal MRI (w/MR angiography) in older persons. | In those w/evidence of spinal involvement (See also Cardiovascular/Vascular in this table.)
Clinical assessment for pain functional impairment |
Constitutional
(undergrowth
or generalized
growth
Source: GeneReviews — "PIK3CA-Related Overgrowth Spectrum"
2 trials found
Table 8. Recommended Surveillance for Individuals with PIK3CA-Related Overgrowth Spectrum
System/Concern | Evaluation | Frequency |
|---|---|---|
restriction) | Measurement of growth parameters, incl head circumference, length of arms, hands, legs,1 feet2 | At each visit; Ultrasound or MRI follow up in those w/truncal overgrowth2; Radiographs of limbs in those w/overgrowth of a limb or portion of a limb; Spinal MRI in those w/scoliosis or deformities that affect the spine |
Neurologic | Serial head MRI imaging | Depending on severity of findings on initial assessment degree of brain maturation3; Monitor those w/seizures as clinically indicated.; Assess for new manifestations incl seizures, changes in tone, other signs/symptoms of Chiari malformation.4,5 |
Behavioral | Behavioral assessment for anxiety, attention, aggressive or self-injurious behavior | At each visit in children, adolescents, adults Musculoskeletal |
malformations | Clinical assessment monitoring, ideally by a vascular anomalies team6 | As clinically indicated |
Genitourinary | Consideration of renal ultrasound | Every 3 mos until age 8 yrs7 |
Hematologic | Hematology consultation w/recommendations for assessment for thrombosis coagulopathy risk | After any surgical intervention, esp in those w/CLOVES phenotype /or vascular malformations Endocrinologic |
Source: GeneReviews — "PIK3CA-Related Overgrowth Spectrum"
Phenotype severity distribution: 12 very common features, 14 common features.
Estimated prevalence: <1 in 1,000,000 (VERY_RARE).
2 clinical trials registered, 2 recruiting. Interventions under study include drug therapy and procedural interventions. Pipeline includes 2 PHASE2. Research is sponsored by a mix of industry and academic institutions.
8 publications have been identified in PubMed for megalencephaly-capillary malformation-polymicrogyria syndrome. Research spans Case Report / Case Series (63%), Review / Meta-Analysis (13%), and Clinical Trial Publication (13%).
Bryan M (2026). [PMID: 41579065](https://pubmed.ncbi.nlm.nih.gov/41579065/). *Pediatric blood & cancer*. [Epidemiology / Natural History]
Anderson S (2025). [PMID: 41064377](https://pubmed.ncbi.nlm.nih.gov/41064377/). *Case reports in genetics*. [Case Report / Case Series]
Gazzin A (2025). [PMID: 39870398](https://pubmed.ncbi.nlm.nih.gov/39870398/). *Journal of medical genetics*. [Case Report / Case Series]
Toaiari F (2025). [PMID: 41041879](https://pubmed.ncbi.nlm.nih.gov/41041879/). *Italian journal of dermatology and venereology*. [Review / Meta-Analysis]
Kaan H (2025). [PMID: 40660698](https://pubmed.ncbi.nlm.nih.gov/40660698/). *Clinical psychopharmacology and neuroscience : the official scientific journal of the Korean College of Neuropsychopharmacology*. [Case Report / Case Series]
Andrade BP (2025). [PMID: 39631263](https://pubmed.ncbi.nlm.nih.gov/39631263/). *Pediatric neurology*. [Case Report / Case Series]
Luu M (2024). [PMID: 39806603](https://pubmed.ncbi.nlm.nih.gov/39806603/). *BMJ open*. [Clinical Trial Publication]
Wedemeyer MA (2024). [PMID: 39455600](https://pubmed.ncbi.nlm.nih.gov/39455600/). *Scientific reports*. [Case Report / Case Series]
Data assembled from 8 of 12 sources · Last updated Sep 18, 2026, 7:59 PM UTC
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Limb |
Hemihyperplasia |
May incl whole limb, part of limb, or only hand or foot (acral overgrowth); May involve soft tissue, muscle, /or bone Macrodactyly |
Lymphatics7 | Isolated lymphatic malformations: dilated vascular channels lined by lymphatic endothelial cells | Fluid-filled cysts usually grow proportionally w/growth of affected person; may pain /or morbidity if they are infiltrative. |
Vascular7 | Vascular malformations | Incl capillary, venous, or mixed malformations Skin |
Source: GeneReviews — "PIK3CA-Related Overgrowth Spectrum"
Megalencephaly-polydactyly-polymicrogyria-hydrocephalus (MPPH) syndrome |
AD (de novo) or somatic |
Brain overgrowth (MEG), polymicrogyria, hydrocephalus, polydactyly, connective tissue or joint laxity |
Absence of consistent vascular/lymphatic malformations or severe focal somatic overgrowth HRAS KRAS |
NRAS | Linear nevus sebaceous syndrome (LNSS) (OMIM 163200) | NA (somatic) | Cutaneous findings (incl epidermal nevi vascular malformations) |
Smith-Kingsmore syndrome | AD (de novo) or somatic | Brain overgrowth (MEG), polymicrogyria, cutaneous findings (incl hyperpigmented nevi) | Absence of consistent vascular/lymphatic malformations PTCH1 SUFU |
Basal cell nevus syndrome | AD | Brain overgrowth (MEG), polydactyly, syndactyly | Calcine calcification, BCCs, jaw cysts, epidermal cysts, wide ribs, many other skeletal other multisystem features |
PTEN | PTEN hamartoma tumor syndrome (PHTS) | AD | Brain overgrowth (MEG), vascular malformations (incl capillary malformations), lipomas |
Source: GeneReviews — "PIK3CA-Related Overgrowth Spectrum"