Falsely elevated C4-carnitine as expression of glutamate formiminotransferase deficiency in tandem mass spectrometry newborn screening

✍ Scribed by Sabrina Malvagia; Giancarlo la Marca; Bruno Casetta; Serena Gasperini; Elisabetta Pasquini; Maria Alice Donati; Enrico Zammarchi

• Publisher: John Wiley and Sons
• Year: 2006
• Tongue: English
• Weight: 100 KB
• Volume: 41
• Category: Article
• ISSN: 1076-5174
• DOI: 10.1002/jms.964

✦ Synopsis

Falsely elevated C4-carnitine as expression of glutamate formiminotransferase deficiency in tandem mass spectrometry newborn screening

After the first report by Millington et al., 1 the development of electrospray tandem mass spectrometry (MS/MS) has enabled in recent years the introduction of expanded newborn screening programs in many countries. 2,3 This has led to an increase in the capacity to detect rare metabolic disorders during the neonatal period.

The increase of the only C4-acylcarnitine, as detected by tandem mass spectrometry in newborn screening, is reported to be related to short chain acyl-CoA dehydrogenase (SCAD) deficiency (butyrylcarnitine) or isobutyryl-CoA dehydrogenase (IBD) deficiency (isobutyrylcarnitine). 4 Expanded Newborn Screening Pilot Program using MS/MS is being conducted in three provinces of Tuscany since January 2001, and, being officially mandated by a legislative action, screens all babies born in Tuscany since November 2004 (approximately 30 000/year) for selected acylcarnitines and amino acids. We report on a newborn in which the screening showed an isolated apparent elevation of C4-acylcarnitine usually associated with SCAD or IBD deficiency. A careful evaluation of the results and the subsequent biochemical investigations allowed us to demonstrate that this alteration was due to accumulation of formiminoglutamate (FIGLU).

Acylcarnitines and amino acids in all dried blood spots from newborn were analysed as butyl esters with the same methodology described by la Marca et al. 5 An Applied Biosystems-Sciex (Toronto, Canada) API 4000 triplequadrupole mass spectrometer equipped with a Turbo V-Spray source was employed.

MS and MS/MS spectra were collected in continuous flow mode by connecting the infusion pump directly to the Turbo V-Spray source. A standard solution of 1 ng/µl of each amino acid and acylcarnitine in water : acetonitrile (30 : 70) containing 0.05% formic acid was infused at 5 µl/ min. Measurements on samples were performed by using a Series 1100 Agilent Technologies (Waldbronn, Germany) CapPump coupled to an Agilent Micro ALS autosampler, both fully controlled from the API 4000 data system. Experimental flow rate was 70 µl/ min using water : acetonitrile (30 : 70) containing 0.05% formic acid. The eluent from the column was directed to the Turbo V-Spray probe. The acquired data were processed using the Analyst 1.4.1 proprietary software including the 'Explore' option (for spectral interpretation) and the ChemoView software (for quantitative information generation).

The child was born from consanguineous Pakistani parents (first cousins) after five uneventful pregnancy. The family history was unremarkable: two brothers and two sisters were normal. The delivery was made by caesarean section because of foetal distress at the 36th week of gestation. At birth, the APGAR score was 9 I and 10 V , weight 2700 g, length 49 cm, and head circumference 33 cm. Since the first days of life, the infant presented poor sucking and brought up milk. Expanded newborn screening for metabolic diseases by tandem mass spectrometry showed levels of C4-acylcarnitine mildly increased (using a cutoff value of the mean C 2SDs). The physical examination at 20 days of life showed normal cardiac, respiratory and abdominal findings and no dysmorphic features. Increased tendon reflex and mild axial hypotonia with hypertonia of legs were present. EEG showed diffuse paroxystic activity. Abdominal and cerebral ultrasound investigations as well as brain auditory-evoked potentials (BAEPs) and visual-evoked potentials (VEPs) were normal. Fundus oculi, ECG and cardiac ultrasound were normal. Laboratory investigations revealed normocytic anaemia (Hb 10,9, MCV 80,1 fl). Plasma and