A useful multi-analyte blood test for cerebrotendinous xanthomatosis.
OBJECTIVE
Cerebrotendinous xanthomatosis (CTX) is a rare genetic disorder of bile acid (BA) synthesis that can cause progressive neurological damage and premature death. Blood (normally serum or plasma) testing for CTX is performed by a small number of specialized laboratories, routinely by gas chromatography-mass spectrometry (GC-MS) measurement of elevated 5α-cholestanol. We report here on a more sensitive biochemical approach to test for CTX particularly useful for confirmation of CTX in the case of a challenging diagnostic sample with 5α-cholestanol that, although elevated, was below the cut-off used for diagnosis of CTX (10 μg/mL or 1.0 mg/dL).


METHODS
We have previously described liquid chromatography-electrospray ionization-tandem mass spectrometry (LC-ESI-MS/MS) methodology utilizing keto derivatization to enable the sensitive quantification of plasma ketosterol BA precursors that accumulate in CTX. We have expanded this methodology to perform isotope dilution LC-ESI-MS/MS quantification of a panel of plasma ketosterol BA precursors, with internal standards readily generated using isotopically-enriched derivatization reagent.


RESULTS
Quantification of plasma ketosterol BA precursors (7α-hydroxy-4-cholesten-3-one, 7α,12α-dihydroxy-4-cholesten-3-one and 7α,12α-dihydroxy-5β-cholestan-3-one) in a single LC-ESI/MS/MS test provided better discrimination between a CTX-positive and negative samples analyzed (n=20) than measurement of 5α-cholestanol alone.


CONCLUSIONS
Quantification of plasma ketosterol BA precursors provides a more sensitive biochemical approach to discriminate between CTX negative and positive samples. A multiplexed LC-ESI-MS/MS test quantifying a panel of plasma ketosterols, with simple sample preparation, rapid analysis time and readily available internal standards, can be performed by most clinical laboratories. Wider availability of testing will benefit those affected with CTX.
Department of Physiology & Pharmacology, Oregon Health & Science University (OHSU), Portland, OR 97239, USA. Electronic address: debarber@ohsu.edu.
Andrea E
AE
DeBarber
Department of Physiology & Pharmacology, Oregon Health & Science University (OHSU), Portland, OR 97239, USA.
Jenny
J
Luo
Medical Genetics Service, Hospital de Clinicas de Porto Alegre, Brazil; Department of Genetics, Federal University of Rio Grande do Sul, Porto Alegre, Brazil.
Roberto
R
Giugliani
Department of Genetics, Federal University of Rio Grande do Sul, Porto Alegre, Brazil.
Carolina F M
CF
Souza
Casey Molecular Diagnostic Laboratory, OHSU, USA.
John Pei-Wen
JP
Chiang
Department of Pediatrics, OHSU, USA.
Louise S
LS
Merkens
Department of Pediatrics, OHSU, USA.
Anuradha S
AS
Pappu
Department of Pediatrics, OHSU, USA; Department of Molecular & Medical Genetics, Child Development & Rehabilitation Center, Doernbecher Children's Hospital, OHSU, USA; Marshfield Research Clinic Foundation, Marshfield, WI 54449, USA.
Robert D
RD
Steiner
D002777:Cholestanols / Q000097:blood; D005260:Female; D006801:Humans; D007664:Ketosteroids / Q000097:blood; D012015:Reference Standards; D021241:Spectrometry, Mass, Electrospray Ionization / Q000592:standards; D053719:Tandem Mass Spectrometry / Q000592:standards; D019294:Xanthomatosis, Cerebrotendinous / Q000097:blood* / Q000175:diagnosis*; D055815:Young Adult
D002777:Cholestanols; D007664:Ketosteroids
Bile acids; CYP27A1; Cerebrotendinous xanthomatosis; Cholestanol; Ketosterols