A blood test for cerebrotendinous xanthomatosis with potential for disease detection in newborns

Cerebrotendinous xanthomatosis (CTX) is a rare, diffi cult-to-diagnose genetic disorder of bile acid (BA) synthesis that can cause progressive neurological damage and premature death. Detection of CTX in the newborn period would be benefi cial because an effective oral therapy for CTX is available to prevent disease progression. There is no suitable test to screen newborn dried bloodspots (DBS) for CTX. Blood screening for CTX is currently performed by GC-MS measurement of elevated 5 - -cholestanol. We present here LC-ESI/MS/MS methodology utilizing keto derivatization with ( O -(3-trimethylammonium-propyl) hydroxylamine) reagent to enable sensitive detection of ketosterol BA precursors that accumulate in CTX. The availability of isotopically enriched derivatization reagent allowed ready tagging of ketosterols to generate internal standards for isotope dilution quantifi cation. Ketosterols were quantifi ed and their utility as markers for CTX was compared with 5 - -cholestanol. 7 - ,12 - - Dihydroxy-4-cholesten-3-one provided the best discrimination between CTX and unaffected samples. In two CTX, newborn DBS concentrations of this ketosterol (120-214 ng/ml) were - 10-fold higher than in unaffected newborn DBS (16.4 ± 6.0 ng/ml), such that quantifi cation of this ketosterol provides a test with potential to screen newborn DBS for CTX. Early detection and intervention through newborn screening would greatly benefi t those affected with CTX by preventing morbidity and mortality.