McCann, Mark

SummaryNewborns identified with profound biotinidase deficiency (BTD) by the Minnesota Newborn Screening Program (MN NBS) between 1 October 2004 and 30 May 2008 were all from new immigrant groups. Thirty‐three positive cases of BTD were identified out of 264 727 infants screened by the Wolf colorimetric system during the period of this study by MN NBS. Five cases of profound BTD (0.1 to <0.6 nmol/min per ml) and 26 cases of partial BTD (0.9 to 2.3 nmol/min per ml) were later confirmed through measurement of serum biotinidase activity. The incidence of combined partial and profound BTD of 1/8540 and that of profound BTD of 1/52 945 in Minnesota are unusually high in comparison with the reported worldwide numbers of 1/61 067 for combined BTD and 1/137 401 for profound BTD. Four out of the 5 cases of profound BTD ascertained in the MN NBS cohort were of Somali ethnic background, and the remaining case was of Asian (Pakistani/Indian) ethnic background. All four Somali patients have the P497S mutation, with one of the four being homozygous for the mutation. The three compound heterozygotes all have a novel mutation (P142T) and two of them have another change (Y428Y) that has never been described. Within the last two decades, Minnesota has become home to an estimated 40 000 Somali immigrants and their children (<1% of the total Minnesota population). New population demographics prompt careful analysis of case cohorts to identify specific groups at risk for rare inborn errors of metabolism.

Abstract Background: Newborn screening for congenital adrenal hyperplasia (CAH) involves measurement of 17α-hydroxyprogesterone (17-OHP), usually by immunoassay. Because this testing has been characterized by high false-positive rates, we developed a steroid profiling method that uses liquid chromatography–tandem mass spectrometry (LC-MS/MS) to measure 17-OHP, androstenedione, and cortisol simultaneously in blood spots. Methods: Whole blood was eluted from a 4.8-mm (3/16-inch) dried-blood spot by an aqueous solution containing the deuterium-labeled internal standard d8-17-OHP. 17-OHP, androstenedione, and cortisol were extracted into diethyl ether, which was subsequently evaporated and the residue dissolved in LC mobile phase. This extract was injected into a LC-MS/MS equipped with pneumatically assisted electrospray. The steroids were quantified in the selected-reaction monitoring mode by use of peak areas in reference to the stable-isotope-labeled internal standard. We analyzed 857 newborn blood spots, including 14 blood spots of confirmed CAH cases and 101 of false-positive cases by conventional screening. Results: Intra- and interassay CVs for 17-OHP were 7.2–20% and 3.9–18%, respectively, at concentrations of 2, 30, and 50 μg/L. At a cutoff for 17-OHP of 12.5 μg/L and a cutoff of 3.75 for the sum of peak areas for 17-OHP and androstenedione divided by the peak area for cortisol, 86 of the 101 false-positive samples were within reference values by LC-MS/MS, whereas the 742 normal and 14 true-positive results obtained by conventional screening were correctly classified. Conclusion: Steroid profiling in blood spots can identify false-positive results obtained by conventional newborn screening for CAH.