Hyperekplexia-4 is an autosomal recessive severe neurologic disorder apparent at birth. Affected infants have extreme hypertonia and appear stiff and rigid. They have little if any development, poor or absent visual contact, and no spontaneous movement, consistent with an encephalopathy. Some patients have early-onset refractory seizures, and many have inguinal or umbilical hernia. Most patients die in the first months of life due to respiratory failure or other complications (summary by {2:Piard et al., 2018}).nnFor a general description and a discussion of genetic heterogeneity of hyperekplexia, see HKPX1 (OMIM:149400). The disease is hyperekplexia 4 (MONDO_0044330, a Monarch Disease Ontology entry).