UNC5D and fetal growth restriction: Third, SLITRK1 regulates the synapse formation between hippocampal neurons and neuronal survival.65,66 To date, only 1 study found that Slitrk1 knockout mice had a lower body weight during postnatal development.67 Last, UNC5D is a netrin receptor that promotes the outgrowth and guidance of spinal axons toward the floor plate during embryogenesis in vertebrates.68 An epidemiological study in 80 mother-newborn pairs69 showed that maternal netrin-4 blood levels decreased as birth weight centiles increased for fetuses with an intrauterine growth restriction.