Hypotonia-cystinuria syndrome

Hypotonia-cystinuria syndrome (HCS) is a rare contiguous gene deletion syndrome caused by deletions on chromosome 2p21 that encompass at least two adjacent genes: SLC3A1 (associated with cystinuria) and PREPL (associated with hypotonia). Because the deletion removes both genes simultaneously, affected individuals present with features of both conditions. The syndrome is also known as 2p21 deletion syndrome. The hallmark features of hypotonia-cystinuria syndrome include neonatal and infantile hypotonia (low muscle tone), failure to thrive, feeding difficulties, and cystinuria — a condition in which excessive amounts of the amino acid cystine are excreted in the urine, predisposing individuals to recurrent kidney stone formation. Affected infants typically present at birth or in the neonatal period with marked hypotonia and poor feeding requiring nutritional support. Growth retardation and developmental delay may also be observed. Some patients may exhibit additional features depending on the extent of the chromosomal deletion, which can occasionally involve neighboring genes. There is no cure for hypotonia-cystinuria syndrome, and management is supportive and symptom-directed. Treatment of cystinuria involves high fluid intake, urinary alkalinization, and in some cases thiol-binding drugs (such as D-penicillamine or tiopronin) to reduce cystine stone formation. Hypotonia and feeding difficulties are managed with physical therapy, occupational therapy, and nutritional support. Regular monitoring of renal function and urinary cystine levels is essential. Early intervention programs can help optimize developmental outcomes in affected children.

Data sourced from FDA regulatory filings and ClinicalTrials.gov. Updated periodically.

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