Clinical, metabolic, and imaging characterization of seven patients followed by homozygosity mapping and linkage analysis were performed. OligoMix was used to generate molecular inversion probes (MIP) and next generation sequencing, bioinformatics, and segregation analyses followed, to determine a loss of function sequence variation in the phospholipase A2-activating protein encoding gene (PLAA). Expression and functional studies of the encoded protein were performed and included measurement of prostaglandin E2 and cytosolic phospholipase A2 activity in membrane fractions of fibroblasts derived from patients and healthy controls. Plaa-null mice were generated and prostaglandin E2 levels were measured in different tissues.
The novel phenotype of their patients was found to be segregated with a homozygous loss-of-function sequence variant, causing the substitution of leucine at position 752 to phenylalanine, in PLAA, which caused disruption of the protein’s ability to induce prostaglandin E2 and cytosolic phospholipase A2 synthesis in patients’ fibroblasts. Plaa-null mice were perinatal lethal with reduced brain levels of prostaglandin E2.
The non-functional phospholipase A2-activating protein and the associated neurological phenotype, reported herein for the first time, join other complex phospholipid defects that cause leukoencephalopathies in humans, emphasizing the importance of this axis in white matter development and maintenance.
PGE2 levels in embryonic mouse tissues. Wild-type, Plaa+/−, and Plaa−/− embryos were sacrificed at embryonic Day 18.5 and organs were isolated and prostaglandin levels determined for the lung (A), brain (B), liver (C), and heart (D). Data represented arithmetic means ± SD from tissues representing three wild-type, three Plaa+/−, and four Plaa−/− embryos and obtained from three independent littermates. Significance was determined by one-way ANOVA with Tukey post hoc correction. *P < 0.05 ***P < 0.001.