Homozygous frameshift variant in NTNG2, encoding a synaptic cell adhesion molecule, in individuals with developmental delay, hypotonia, and autistic features

Regulation of neuronal connectivity and synaptic communication are key to proper functioning of the brain. The Netrin-G subfamily and their cognate receptors are vertebrate-specific synaptic cell adhesion molecules with a role in synapse establishment and function, which seem to have co-evolved to contribute to higher brain functions. We identified a homozygous frameshift variant in NTNG2 (NM_032536.3: c.376dup), encoding Netrin-G2, in eight individuals from four families with global developmental delay, hypotonia, secondary microcephaly, and autistic features. Comparison of haplotypes established this as a founder variant. Previous studies showed that Ntng2-knockout mice have impaired visual, auditory, and motor coordination abilities required for demanding tasks, as well as possible spatial learning and memory deficits. Knockout of Ntng2 in a cellular model resulted in short neurites, and knockout of its trans-synaptic partner Ngl2/Lrrc4 in mice revealed autistic-like behavior and reduced NMDAR synaptic plasticity. The Ngl2/Lrrc4-knockout mouse phenotype was rescued by NMDAR activation, suggesting a mechanistic link to autism spectrum disorder. We thus propose NTNG2 as a candidate disease gene and provide further support for the involvement of Netrin-G2 in neuropsychiatric phenotypes.