A total of 24 cases of IVA and 3 cases of SBCADD were detected (Fig.
The resulting total incidence for IVA was 1:67 000 (95% CI: 1:45 000-1:107 000), whereas the total incidence for SBCADD was 1:403 000 (95% CI: 1:161 0001:1 612 000).
With this strategy all cases of IVA, including the variant cases, but only 1 of the 4 cases of SBCADD would have been detected.
The suggestion that SBCADD is a benign biochemical variant has been based on the finding that individuals identified by NBS have remained asymptomatic so far, even without treatment, and also on the identification by family screening of asymptomatic individuals with the condition (2, 17).
4] Nonstandard abbreviations: IVA, isovaleric acidemia; CoA, coenzyme A; C5, isovalerylcarnitine; NBS, newborn screening; SBCADD, short/branched-chain acyl-CoA dehydrogenase (2-methylbutyryl-CoA dehydrogenase) deficiency; PPV, positive predictive value; ESI-MS/MS, electrospray ionization-tandem mass spectrometry; C8, octanoylcarnitine; C4, butyrylcarnitine; C3, propionylcarnitine.
The first identified patient with SBCADD was reported only in the year 2000 (1).
Judging by the number of diagnosed patients, SBCADD would appear to be a rare disorder.
Awareness of 2-ethylhydracrylic aciduria as an indicator of SBCADD may lead to increasing diagnosis of this disorder and further definition of its phenotype.
Patient 1 with SBCADD was identified by newborn screening and is healthy with normal development, whereas patients 2-4 were identified after metabolic studies performed for evaluation of clinical disease.
In all samples there was increased excretion not only of 2-MBG, as expected in SBCADD, but also of 2-EHA.
In the samples from the SBCADD patients, the height of the 2-EHA peak always exceeded that of the 2-MBG peak, with the exception of patient 4 (Fig.
It is noteworthy that the blood-spot C5 carnitine concentration was within the reference interval in one of the first reported SBCADD patients (2).