The 2p21 microdeletion syndrome consists of cystinuria, neonatal seizures, hypotonia, severe growth and developmental delay, facial dysmorphism, and lactic acidemia. It has been described in seven patients from three families of a small Bedouin clan. Dysmorphic features include frontal bossing, almond-shaped eyes, long eyelashes, depressed nasal bridge, and large, posteriorly rotated ears. Renal lithiasis occurs at an early age in all patients. Reduced activity of the respiratory chain complexes I, III, IV and V was found in patients examined. The syndrome is caused by homozygous deletion of at least four contiguous genes on chromosome 2: SLC3A1, PREPL, PPM1B and C2orf34 (2p21).