ISLR2 (immunoglobulin superfamily containing leucine-rich repeat 2), encodes a protein involved in axon guidance in brain development (hence the other name leucine-rich repeat domain- and immunoglobulin domain-containing axon extension proteins; LINX). A recently described mouse knockout displays hydrocephalus. However, the corresponding phenotype in humans is unknown. Here, we describe a multiplex consanguineous family in which a homozygous truncating variant in ISLR2 segregates with severe congenital hydrocephalus, arthrogryposis multiplex congenita and abdominal distension. We suggest this syndrome may represent the human "knockout" phenotype for ISLR2.