Hepatic Carnitine Palmitoyltransferase I
Deficiency: Acylcarnitine Profiles in Blood Spots
Are Highly Specific
Ralph Fingerhut,
1*
Wulf Ro ¨ schinger,
2
Ania C. Muntau,
2
Torsten Dame,
1
Jens Kreischer,
1
Ralf Arnecke,
1
Andrea Superti-Furga,
3
Heinz Troxler,
3
Bernhard Liebl,
4
Bernhard Olgemo ¨ ller,
1
and Adelbert A. Roscher
2
Background: In carnitine palmitoyltransferase I (CPT-I)
deficiency (MIM 255120), free carnitine can be increased
with no pathologic acylcarnitine species detectable. As
inclusion of CPT-I deficiency in high-risk and newborn
screening could prevent potentially life-threatening
complications, we tested whether CPT-I deficiency
might be diagnosed by electrospray ionization-tandem
mass spectrometry (ESI-MS/MS).
Methods: A 3.2-mm spot of whole blood dried on filter
paper was extracted with 150 L of methanol. After
derivatization of carnitine and acylcarnitines to their
butyl esters, the samples were analyzed by ESI-MS/MS
with 37.5 pmol of L-[
2
H
3
]carnitine and 7.5 pmol of
L-[
2
H
3
]palmitoylcarnitine as internal standards.
Results: In all dried-blood specimens from each of three
patients with CPT-I deficiency, we found an invariably
increased ratio of free carnitine to the sum of palmitoyl-
carnitine and stearoylcarnitine [C0/(C16 C18)]. The
ratio in patients was between 175 and 2000, or 5- to
60-fold higher than the ratio for the 99.9th centile of the
normal newborn population in Bavaria (n 177 842).
No overlap with the values of children that were known
to be supplemented with carnitine was detected [C0/
(C16 C18), 34 30; mean SD; n 27].
Conclusions: ESI-MS/MS provides a highly specific
acylcarnitine profile from dried-blood samples. The
ratio of free carnitine to the sum of palmitoylcarnitine
and stearoylcarnitine [C0/(C16 C18)] is highly specific
for CPT-I deficiency and may allow presymptomatic
diagnosis.
© 2001 American Association for Clinical Chemistry
In carnitine palmitoyltransferase I (CPT-I)
5
deficiency
(MIM 255120), long-chain fatty acids are not transferred
from CoA to carnitine to form acylcarnitines by palmitoyl-
CoA:l-carnitine O-palmitoyltransferase (EC 2.3.1.21).
Thus, they cannot enter the mitochondria for subsequent
-oxidation (1). There are two distinct tissue-specific
isoforms of the enzyme: the liver-type isoform (CPT-IA)
and the muscle-type isoform (CPT-IB) (2, 3). The two
isoforms are encoded by two different genes (4). Whereas
CPT-IA is expressed in liver, kidney, and fibroblasts and
CPT-IB is expressed in skeletal muscle, cardiac ventricular
myocytes are the only cells known to express both iso-
forms. CPT-IA and CPT-IB are subject to different types of
regulation. CPT-IA is inhibited by malonyl-CoA, whereas
a high-fat diet increases CPT-IA expression specifically in
the liver (5). Therefore, CPT-IA is the key enzyme in the
regulation of fatty acid oxidation. Twenty-two patients
with CPT-IA deficiency in 17 families have been reported
to date. All patients have CPT-IA deficiency (6), which
will subsequently be called “CPT-I”. To date, there has
been no report of a patient with CPT-IB deficiency.
Children with CPT-I deficiency usually present with
life-threatening attacks of fasting hypoketotic hypoglyce-
mia and coma during the first 2 years of life. Persistent
neurologic deficits are common. These children usually
do not have cardiac or skeletal muscle involvement.
However, four new cases were recently described that
1
Labor Becker, Olgemo ¨ ller & Kollegen, D-81671 Munich, Germany.
2
Dr. von Hauner Children’s Hospital, Department of Clinical Chemistry
and Biochemical Genetics, Ludwig-Maximilians-University, D-80337 Munich,
Germany.
3
University Children’s Hospital, CH-8032 Zurich, Switzerland.
4
Public Health Screening Center, D-80764 Oberschleissheim, Germany.
*Address correspondence to this author at: Labor Becker, Olgemo ¨ller &
Kollegen, Fu ¨ hrichstrasse 70, D-81671 Munich, Germany. Fax 49-89-544-654-10;
e-mail fingerhu@labor-bo.de.
Received March 21, 2001; accepted June 22, 2001.
5
Nonstandard abbreviations: CPT-I, carnitine palmitoyltransferase I;
MCT, medium-chain triacylglycerol; ESI-MS/MS, electrospray ionization–
tandem mass spectrometry; and EEG, electroencephalogram.
Clinical Chemistry 47:10
1763–1768 (2001)
Molecular Diagnostics
and Genetics
1763