PIK3CA and overgrowth syndrome: PIP3 generation triggers activation of downstream effectors including PDK1 and then AKT, which promote cell growth and survival.6 Somatic mosaic activating variants in PIK3CA, encoding the p110α catalytic subunit of the PI3K heterodimer, have been well described in vascular malformations and overgrowth syndromes.7 Among the regulatory subunits of PI3K, PIK3R1 encodes three distinct protein products (p85α, p55α and p50α), generated through alternative splicing.