An Extremely Preterm Infant With PIK3CA-Related Overgrowth Spectrum (PROS): Alpelisib Treatment and Outcome.

Phosphatidylinositol 4,5-bisphosphate 3-kinase catalytic subunit alpha (PIK3CA)-related overgrowth spectrum (PROS) is a group of rare genetic asymmetric and atypical overgrowth disorder syndromes. Affecting skin, adipose and connective tissues, brain, bone, and vasculature and severity influenced by the gestational age at which the change occurred, PROS is phenotypically heterogeneous. This paper shares the case report of a former extremely preterm infant diagnosed with a subtype of PROS, megalencephaly-capillary malformation/megalencephaly-capillary malformation polymicrogyria (MCAP) syndrome, for whom treatment with alpelisib was initiated at 10 months of age (7 months corrected age). To our knowledge, this patient is the third and youngest to be included in this expanded access program for compassionate use for patients under 2 years of age.