Abstract: Disclosed are new approaches to detecting adenosine deaminase (ADA) deficiency. There is provided a method of determining ADA activity, comprising: dividing a sample obtained from blood into two portions, adding an ADA inhibitor to one portion, measuring levels of ADA activity in both portions, and determining the ADA activity. Also provided is a method of measuring ADA substrate, comprising: measuring an ADA substrate in a sample obtained from blood of subject, and comparing this to at least one control sample obtained from blood and comprising an ADA inhibitor, and a known quantity of the ADA substrate. Multiplexed methods of measuring ADA enzymatic activity along with other metabolic markers are also provided. The methods are particularly useful for the analysis of samples obtained from dried blood spots (DBSs), and may be incorporated into existing newborn screening programs. Associated diagnostic methods, control samples, and apparatuses are also disclosed.

Abstract: There is provided a method of measuring methylcitrate (MCA) in a sample by derivatizing the MCA, for example with 4-[2-(N,N-dimethylamino)ethylaminosulfonyl]-7-(2-aminoethylamino)-2,1,3-benzoxadiazole (DAABD-AE); measuring a level of the derivatized MCA; and determining the level of MCA from the measured level. The sample may be a dried blood spot (DBS), and the extraction and derivatization may be carried out simultaneously. No separate extraction or purification step is required, thereby reducing sample handling. Measuring may be carried out by mass spectrometry. The method may be used to screen for subjects having or at increased risk of a propionylcarnitine (C3) related disorder. The method may be used as a first tier screen, or as a second tier test for a sample that previously triggered a positive result in a primary screen. The method may be applied to newborn screening. Related kits and uses are also provided.