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Any overgrowth syndrome where the cause of the disease is a gain-of-function variant in the AKT3 gene.
No HPO annotations are available for this condition.
MPPH syndrome is a developmental brain disorder characterized by megalencephaly (brain overgrowth) with the cortical malformation bilateral perisylvian polymicrogyria. To date, fewer than than 100 individuals with features of MPPH syndrome have been reported with either a clinical diagnosis (presence of the 2 core clinical and imaging findings: megalencephaly and polymicrogyria) , and/or a molecularly confirmed diagnosis [, , , , , , , , , , , , , , , , , , , ]. Table 2. MPPH Syndrome: Frequency of Select Features
MPPH syndrome should be suspected in individuals with the following clinical and imaging findings . Note: Findings shown in bold are core features.
Clinical findings
Macrocephaly or megalencephaly (occipital frontal circumference ≥2 SD above the mean); onset either prenatally or postnatally
Postaxial polydactyly of one or more extremities
No approved treatments are currently available for AKT3-related overgrowth spectrum. The disease remains an area of unmet medical need.
To establish the extent of disease and needs in an individual diagnosed with megalencephaly-postaxial polydactyly-polymicrogyria-hydrocephalus (MPPH) syndrome, the evaluations summarized (if not performed as part of the evaluation that led to diagnosis) are recommended.
Table 5.
Given the limited number of individuals reported with MPPH syndrome, formal surveillance guidelines do not exist. Table 7. Recommended Surveillance for Individuals with MPPH Syndrome
System/Concern |
|---|
No clinical trials have been registered for AKT3-related overgrowth spectrum.
3 publications have been identified in PubMed for AKT3-related overgrowth spectrum. Research spans Review / Meta-Analysis (33%), Basic Science / Preclinical (33%), and Epidemiology / Natural History (33%).
Prina ML (2026). [PMID: 41802265](https://pubmed.ncbi.nlm.nih.gov/41802265/). *Brain*. [Basic Science / Preclinical]
Miremberg H (2026). [PMID: 41353713](https://pubmed.ncbi.nlm.nih.gov/41353713/). *Prenat Diagn*. [Epidemiology / Natural History]
Wang X (2025). [PMID: 40032969](https://pubmed.ncbi.nlm.nih.gov/40032969/). *Sci Rep*. [Review / Meta-Analysis]
Data assembled from 3 of 12 sources · Last updated Sep 20, 2026, 11:24 AM UTC
Common questions about AKT3-related overgrowth spectrum
Feature | % of Persons w/Feature | Comment |
|---|---|---|
Megalencephaly | 100% | — |
Cortical malformations | 100% | Typically BPP but other types of PMG have also been seen |
Hydrocephalus | ~50% | Ventriculomegaly seen in most individuals |
Oromotor dysfunction | ~50% | Specifically assoc w/BPP |
Hypotonia | ~80% | — |
Epilepsy | ~100% | — |
Intellectual disability | 100% | — |
Postaxial polydactyly | 50% | BPP = bilateral perisylvian polymicrogyria; PMG = polymicrogyria Megalencephaly (brain overgrowth). Most individuals with MPPH syndrome reported to date have congenital or early postnatal megalencephaly (i.e., rapidly progressive megalencephaly within the first year of life). |
Source: GeneReviews — "MPPH Syndrome"
Hypotonia
Early-onset epilepsy
Intellectual disability
Oromotor dysfunction (including speech/swallowing difficulties, excessive drooling, expressive speech delays)
Imaging findings
Source: GeneReviews — "MPPH Syndrome"
Table 4. Genes of Interest in the Differential Diagnosis of MPPH Syndrome
Gene(s) | DiffDx Disorder | MOI | Features of DiffDx Disorder |
|---|---|---|---|
MTOR | MTOR-related disorders2 | De novo / somatic mosaic | MEG (congenital or postnatal); PMG (incl BPP) |
PIK3CA | MCAP syndrome (See PIK3CA-Related Overgrowth Spectrum.) | De novo / somatic mosaic1 | MEG (congenital or postnatal); BPP; postaxial polydactyly; ventriculomegaly or hydrocephalus |
Nevoid basal cell carcinoma syndrome | AD | MEG, polydactyly | Calcine calcification, BCCs, jaw cysts, epidermal cysts, wide ribs, many other skeletal multisystem features PTEN |
PTEN hamartoma tumor syndrome | De novo / AD3 | MEG (congenital or postnatal); focal segmental cortical malformations (rare) | Papillomatous papules; trichilemmomas; vascular malformations (hemangiomas, arteriovenous malformations); cancer predisposition (thyroid, breast, endometrium) |
STRADA (LYK5) | STRADA-related disorders (OMIM 611087) | AR | MEG (congenital or postnatal); early-onset epilepsy |
Source: GeneReviews — "MPPH Syndrome"
System/Concern | Evaluation | Comment
| Physical exam w/particular attn to head size (OFC) |
| Assessment by pediatric neurologist w/eval of suspected seizures as indicated | • To incl baseline brain MRI careful eval for medulloblastoma, incl diffusion-weighted imaging to differentiate early neoplastic transformation w/in dysplastic cerebellar tissue early consideration of contrast-enhanced studies in suspicious cases
In the presence of hydrocephalus /or cerebellar tonsillar ectopia, full spinal MRI to evaluate for syringomyelia or syrinx formation
Gastrointestinal/
| Feeding assessment by feeding specialist, nutritionist, gastroenterologist for evidence of chewing swallowing difficulties dysphagia | Consider eval for gastric tube placement as needed.
| Developmental assessment | • To incl motor, adaptive, cognitive, speech/language eval
Eval for early intervention / special education
| Referral to orthopedist as needed for polydactyly |
Eyes | Ophthalmologic eval | To assess for vision abnormalities
| Echocardiogram | To...
Source: GeneReviews — "MPPH Syndrome"
Search ClinicalTrials.gov in the US and EU Clinical Trials Register in Europe for access to information on clinical studies for a wide range of diseases and conditions. Note: There may not be clinical trials for this disorder.
Source: GeneReviews — "MPPH Syndrome"
View trials for AKT3-related overgrowth spectrum
Evaluation
Frequency |
|---|
medulloblastoma | Careful eval of serial brain imaging w/particular attn to posterior fossa for medulloblastoma | Consider brain imaging every 6 mos for medulloblastoma risk. Feeding |
Endocrine | Endocrine eval for hypoglycemia, GHD /or thyroid issues | As recommended by endocrinologist Family/ |
Community | Assess family need for social work support (e.g., palliative/respite care, home nursing, other local resources), care coordination or follow-up genetic counseling if new questions arise (e.g., family planning). | At each visit GHD = growth hormone deficiency |
Source: GeneReviews — "MPPH Syndrome"
AI-curated news mentioning AKT3-related overgrowth spectrum
Updated Jul 21, 2026
FDA approved Casgevy CRISPR gene therapy for children as young as 2 with sickle cell disease on July 1, 2026. Here's what families need to know about this milestone. Approximately 5,500 additional American children are now eligible for this established one-time therapy, according to Vertex Pharmaceuticals, Casgevy's developer. Casgevy also covers transfusion-dependent beta-thalassemia in this new age indication. Sickle cell disease is a lifelong inherited blood disorder that warps red blood cells into stiff, crescent shapes that can block blood flow, starving organs and tissues of oxygen. The world's first CRISPR-based gene therapy has been approved for children as young as two years old, opening the possibility of a single, potentially curative treatment to thousands of American children with sickle cell disease before years of organ damage can narrow what medicine can do for them. Families with children aged 2 and older who have sickle cell disease should speak with their pediatric hematologist about whether Casgevy is appropriate to consider at this stage of their child's disease. Ask specifically which authorized treatment centers perform Casgevy in your region. Treatment is available only at specialized sites, and geographic access remains limited. Contact your child's insurance plan or Medicaid office to ask about coverage. Medicaid coverage for gene therapies varies by state, and some states have developed outcomes-based payment models for high-cost therapies. "With today's decision, pediatric patients as young as 2 years of age can now access a critical additional treatment option to treat these debilitating, life-threatening diseases," said Karim Mikhail, acting director of the Office of Therapeutic Products at the FDA's Center for Biologics Evaluation and Research, according to the FDA press announcement. Casgevy is a non-viral, ex vivo CRISPR/Cas9 gene-edited cell therapy.
A new treatment for children aged 2 or older with sickle cell disease has been approved by the U.S. Food & Drug Administration. In a press release on Wednesday, the FDA announced it had approved Casgevy, the first gene therapy for children with sickle cell disease. (NewsNation) — A new treatment for children aged 2 or older with sickle cell disease has been approved by the Food & Drug Administration (FDA). In a Wednesday news release, the FDA announced it had approved Casgevy, the first gene therapy for children with the disease. “Casgevy is a gene therapy consisting of the patient’s own (autologous) hematopoietic (blood) stem cells, administered as a one-time single dose for intravenous infusion,” the release noted. “Pediatric patients as young as 2 years of age can now access a critical additional treatment option to treat these debilitating, life-threatening diseases,” Karim Mikhail, the acting director of the Center for Biologics Evaluation and Research, wrote. “These disorders carry a heavy burden for children and their families, affecting growth, development, and long-term health in profound ways,” Megha Kaushal, acting deputy director of the Office of Therapeutic Products in CBER, said in the release.