Hypotonia-Failure To Thrive-Microcephaly Syndrome Watchlist (log in to enable) Retrieved 2021-01-23 Source Orphanet Trials — Genes LTC4S Drugs — Interested in hearing about new therapies? Registered! Leukotriene C4 synthase deficiency is an extremely rare fatal neurometabolic developmental disorder characterized clinically by muscular hypotonia, psychomotor retardation, failure to thrive, and microcephaly.