Rare variants inPPFIA3cause delayed development, intellectual disability, autism, and epilepsy

Abstract

AbstractPPFIA3encodes the Protein-Tyrosine Phosphatase, Receptor-Type, F Polypeptide-Interacting Protein Alpha-3 (PPFIA3), which is a member of the LAR protein-tyrosine phosphatase-interacting protein (liprin) family involved in synaptic vesicle transport and presynaptic active zone assembly. The protein structure and function are well conserved in both invertebrates and vertebrates, but human diseases related to PPFIA3 dysfunction are not yet known. Here, we report 14 individuals with rare mono-allelicPPFIA3variants presenting with features including developmental delay, intellectual disability, hypotonia, autism, and epilepsy. To determine the pathogenicity ofPPFIA3variantsin vivo, we generated transgenic fruit flies expressing either human PPFIA3 wildtype (WT) or variant protein using GAL4-UAS targeted gene expression systems. Ubiquitous expression with Actin-GAL4 showed that thePPFIA3variants had variable penetrance of pupal lethality, eclosion defects, and anatomical leg defects. Neuronal expression with elav-GAL4 showed that thePPFIA3variants had seizure-like behaviors, motor defects, and bouton loss at the 3rdinstar larval neuromuscular junction (NMJ). Altogether, in the fly overexpression assays, we found that thePPFIA3variants in the N-terminal coiled coil domain exhibited stronger phenotypes compared to those in the C-terminal region. In the loss-of-function fly assay, we show that the homozygous loss of flyLiprin-α leads to embryonic lethality. This lethality is partially rescued by the expression of humanPPFIA3WT, suggesting human PPFIA3 protein function is partially conserved in the fly. However, thePPFIA3variants failed to rescue lethality. Altogether, the human and fruit fly data reveal that the rarePPFIA3variants are dominant negative loss-of-function alleles that perturb multiple developmental processes and synapse formation.