Quantitative Analytical Method for the Determination of Biotinidase Activity in Dried Blood Spot Samples

Accurate determination of Biotinidase activity in serum by HPLC and its utilization as second tier test for the confirmation of initial positive newborn screening results

Diagnosis of Biotinidase deficiency (BTD) is extremely important to avoid several neurodevelopmental problems in early childhood. Colorimetric and fluorometric methods lack specificity and selectivity due to several interferences resulting in a high number of false positive results. We developed an HPLC method for BTD activity in serum with fluorescent detection. In colorimetric assays, biotinidase attacks the amide linkage of the artificial substrate biotinidyl-4-aminobenzoic acid (B-PABA) and releases p-aminobenzoic acid (PABA), which is converted to a purple dye by diazotization reaction. The newly developed method injects the reaction mixture directly into the HPLC column and quantifies using a six-point calibration curve without coupling and diazotization reaction. The method is linear over the 5-1000 μmol/L range. The detection and quantitation limits were 2.5 μmol/L and 5.0 μmol/L, respectively. When compared with colorimetric assay, the correlation coefficient (R2) was 0.9963. The within-assay and between-assay precision was <10.0% for four levels of quality control samples. No significant variation in BTD activity was detected due to hemolysis, icteric, and lipemic samples. The newly developed method eliminates the potential interference due to the presence of aromatic amines and significantly reduces the false positive results observed with the colorimetric method. It is simple, specific, sensitive, faster in sample preparation, and requires a small sample volume. The newly developed HPLC method was used in our laboratory as a secondary tier test for initial positive BTD samples from newborn screening programs. To our knowledge, no similar HPLC method has been reported to date.

Analysis of Biotinidase Activity in Serum by Digital Imaging Colorimetry Detection

Biotinidase deficiency (BD) is an autosomal recessive inherited disorder of biotin recycling that leads to neurological and cutaneous consequences if left untreated. The clinical features of BD can be ameliorated or prevented by the administration of pharmacological doses of the vitamin biotin. Since it is a treatable disorder, BD is included in the newborn screening program in Türkiye as in many other countries. Therefore, monitoring of biotinidase enzyme activity (BEA) is of vital importance, especially for patients. The aim of this study was to develop a simple and reliable colorimetric method based on digital imaging for the analysis of BEA in serum samples. To determine the optimum distance and LED light source in the analyzer box that we fabricated in the laboratory, images of the solutions in a 96-well microplate were taken with a mobile phone camera, and each color space was examined. The most reliable relationship was between blank subtracted intensities of green channel and analyte concentrations, which was in the range of 35-400 ng/mL p-aminobenzoic acid (r2 = 0.999). The limit of detection and limit of quantification were 11 and 35 ng/mL, respectively. The proposed method was successfully applied to serum samples of 60 patients with BD and 60 healthy controls. We claim that the method can be easily performed for determination of BEA anywhere without needing expensive instruments.

Laboratory diagnosis of biotinidase deficiency, 2017 update: a technical standard and guideline of the American College of Medical Genetics and Genomics

Disclaimer: These ACMG Standards and Guidelines are intended as an educational resource for clinical laboratory geneticists to help them provide quality clinical laboratory genetic services. Adherence to these Standards and Guidelines is voluntary and does not necessarily assure a successful medical outcome. These Standards and Guidelines should not be considered inclusive of all proper procedures and tests or exclusive of others that are reasonably directed to obtaining the same results. In determining the propriety of any specific procedure or test, clinical laboratory geneticists should apply their professional judgment to the specific circumstances presented by the patient or specimen. Clinical laboratory scientists and geneticists are encouraged to document in the patient's record the rationale for the use of a particular procedure or test, whether or not it is in conformance with these Standards and Guidelines. They also are advised to take notice of the date any particular guideline was adopted, and to consider other relevant medical and scientific information that becomes available after that date. It also would be prudent to consider whether intellectual property interests may restrict the performance of certain tests and other procedures.Biotinidase deficiency is an autosomal recessively inherited disorder of biotin recycling that is associated with neurologic and cutaneous consequences if untreated. Fortunately, the clinical features of the disorder can be ameliorated or prevented by administering pharmacological doses of the vitamin biotin. Newborn screening and confirmatory diagnosis of biotinidase deficiency encompasses both enzymatic and molecular testing approaches. These guidelines were developed to define and standardize laboratory procedures for enzymatic biotinidase testing, to delineate situations for which follow-up molecular testing is warranted, and to characterize variables that can influence test performance and interpretation of results.