Homozygous deletion of chromosome 2p21, containing two closely located genes, SLC3A1, and PREPL, has been linked to the hypotonia–cystinuria syndrome. Symptoms include generalized hypotonia at birth, failure to thrive, cystinuria, and growth retardation. The disease is homozygous 2p21 microdeletion syndrome (EFO_0700082, an Experimental Factor Ontology identifier). Also known as: 2p21 contiguous gene deletion syndrome.