O2 LRRC4 variants are associated with predominant speech delay, intellectual disability and alterations in neuronal morphology and synapse numbers

Leucine-Rich Repeat Containing 4 (LRRC4) protein, also known as netrin-G ligand 2 (NGL-2), is mainly localised to postsynaptic excitatory synapses and is involved in synapse formation and neurite extension. Recent data suggest that LRRC4 dysfunction is linked to Autism Spectrum Disorder (ASD) and Intellectual Disability (ID). We used GeneMatcher to identify 20 individuals with LRRC4 gene variants from 17 different families across 9 countries. The core characteristics described are speech delay, ID, ASD and motor delay, with seizures as a supporting feature. 13 males and 7 females were included, aged 1 to 55 years. 15 individuals had loss of function variants, 4 had missense and there was one 5′ untranslated region variant. Further, we generated a Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)-edited human induced pluripotent stem cell (hiPSC) line containing the de novo predicted loss of function LRRC4 variant NM_022143.4:c.843_858del. LRRC4 mutant hiPSCs differentiated into human glutamatergic neurons (iNeurons) show decreased LRRC4 protein expression, less complex neurite branching, and lower number of synapses. These iNeurons also have synapses that are larger in size. Together, this work demonstrates LRRC4 is a novel disease-causing gene and provides insights for therapeutic development.