Acronym for Megalencephaly-Polymicrogyria-Polydactyly-Hydrocephalus

Incidence < 1/1.106. Generally caused by a de novo but sometimes autosomal dominant transmission mutation of the PIK3R2 (19p13.11)(type 1) [MIM 603 387], AKT3 (1q43-q44) (sometimes a duplication 1q43-q44) (type 2) [MIM 615 937], or CCND2 (12p13.32) (type3) [MIM 615 938] gene. This disease of brain development is usually caused by germline mutations but somatic mosaics have been described. The phenotype is close to the megalencephaly-capillary malformation syndrome or CAPM (see this term).

Association of:

-        megalencephaly: the head circumference varies from normal to more than 6 × the standard deviation for age; later it varies from + 3 to + 10 standard deviations for age; a Chiari malformation is sometimes present

-        bilateral perisylvial polymicrogyria leading to neurological disorders: hypotonia, oral dysfunction (dysphagia, severe drooling, speech disorders) (100 %), epilepsy (100 %), moderate to severe intellectual deficit (100 %)

-        post-axial hexadactyly (50 %)

-        hydrocephalus: ventriculomegaly is present in almost all patients but 50 % have true hydrocephalus

-        sometimes: feeding problems (gastrostomy), visual disorders, cardiac malformation (ASD, VSD)

Anesthetic implications:

epilepsy, large head, risk of intracranial hypertension

References :

-        Tohyama J, Akasaka N, Saito N, Yoshimura J, Nishiyama K, Kato M.
Megalencephaly and polymicrogyria with polydactyly syndrome.
Pediatr Neurol 2007 ; 37 : 148-51.

Updated: September 2021