Hypotonia-Cystinuria syndrome (HCS) is a rare disease, caused by a mutation in two contiguous genes (SLC3A1 and PREPL) localized on chromosome 2p21, and it is characterized by both renal involvement with cystine stones and nervous involvement with hypotonia.
Hypotonia-cystinuria syndrome is a very rare autosomal recessive contiguous gene deletion syndrome of PREPL and SLC3A1 at 2p21 with neuromuscular and neuroendocrinologic presentation.
Different recessive contiguous gene deletion syndromes involving PREPL and a variable combination of SLC3A1 (hypotonia-cystinuria syndrome), CAMKMT (atypical hypotonia-cystinuria syndrome), and PPM1B (2p21 deletion syndrome) have been described.
In addition to isolated cystinuria, patients suffering from the hypotonia-cystinuria syndrome have been reported carrying deletions including at least the SLC3A1 and the PREPL genes in 2p21.
Taken together, these results suggest that PREPL is a novel oligopeptidase, with unique structural and functional characteristics, involved in hypotonia-cystinuria syndrome.
The prolyl endopeptidase-like protein PREPL has recently attracted attention because its gene is located within two contiguous gene-deletion syndromes, the 2p21 deletion syndrome and the hypotonia-cystinuria syndrome.