Biallelic null variants in PNPLA8 cause microcephaly through the reduced abundance of basal radial glia

Abstract

PNPLA8, one of the calcium-independent phospholipase A2 enzymes, is involved in various physiological processes through the maintenance of membrane phospholipids. However, little is known about its role in brain development. Here, we report 12 individuals from 10 unrelated families with biallelic ultra-rare variants in PNPLA8 presenting with a wide spectrum of clinical features ranging from developmental and epileptic-dyskinetic encephalopathy (DEDE) to progressive movement disorders. Complete loss of PNPLA8 was associated with the severe end of the spectrum, showing DEDE manifestations and congenital or progressive microcephaly. Using cerebral organoids generated from human induced pluripotent stem cells, we found that loss of PNPLA8 reduced the number of basal radial glial cells (bRGCs) and upper-layer neurons. By spatial transcriptomic analysis targeting apical radial glial cells (aRGCs), we found the downregulation of bRGC-related gene sets in patient-derived cerebral organoids. Lipidomic analysis revealed a decrease in the amount of lysophosphatidic acid, lysophosphatidylethanolamine, and phosphatidic acid, indicative of the disturbed phospholipid metabolism in PNPLA8 knockout neural progenitor cells. Our data suggest that PNPLA8 has a critical role in the bRGC-mediated expansion of the developing human cortex by regulating the fate commitment of aRGCs.