Improved Identification of Partial Biotinidase Deficiency by Newborn Screening Using Age-Related Enzyme Activity Cutoffs: Reduction of the False-Positive Rate

Nicole Vanvleck,Harry Hawkins,Kristin Monaghan,Barry Wolf,Bonita Taffe,Mary Seeterlin,Eleanor Stanley

doi:10.3390/ijns1010045

Abstract

Background: Biotinidase deficiency is an inherited metabolic disorder that if untreated can result in neurological and cutaneous features. Profound biotinidase deficiency presents in early childhood with severe symptoms, whereas partial biotinidase deficiency can also present with symptoms under times of stress. Symptoms can be prevented by administering biotin. Newborn screening for the disorder is performed using dried blood spots. We examined the relationship between biotinidase activity and age at collection to determine how best to identify infants with partial biotinidase deficiency. Methods: Biotinidase activity in dried blood spots is determined using a quantitative fluorometric assay. Subsequent specimens with biotinidase activity ≤100 U were analyzed by mutation analysis to determine the range of activities expressed in infants with partial biotinidase deficiency. Results: Enzyme activity increased with age, beginning at about three days of age, and rose until plateauing at about 11 days of age. An increase of about 47.6% was observed. A total of 54 specimens had mutation analysis performed identifying 20 affected infants who would not have been identified using the original cutoff activity of 50 U. Conclusion: Biotinidase activity in infants increases with age. Age-related cutoffs assist in selectively identifying infants with partial biotinidase deficiency.

Highlights

Biotinidase (EC 3.5.1.12) is the enzyme that cleaves biotin bound to protein to recycle free biotin from biocytin, the product the proteolytic degradation of biotinlylated proteins [1,2]
Positive (S+, infants directly referred for diagnostic testing) and borderline positive (B+, infants requiring a repeat dried blood spot specimen) cutoff activities were established for the PerkinElmer Neonatal Biotinidase Kit by testing 5000 dried blood spots from normal infants and dried blood spots from infants confirmed to have biotinidase deficiency
The S+ cutoff activity was established at 34 U (0.01 percentile); above the enzyme activities of all infants confirmed to have profound biotinidase deficiency

Summary

Introduction

Biotinidase (EC 3.5.1.12) is the enzyme that cleaves biotin bound to protein to recycle free biotin from biocytin, the product the proteolytic degradation of biotinlylated proteins [1,2]. An autosomal recessively inherited disorder caused by deficient activity of biotinidase (OMIM: 253260) can produce neurological and cutaneous symptoms, including seizures, hypotonia, skin rash and alopecia, usually between the second to fifth months of life [3,4]. Children with profound biotinidase deficiency (less than 10% of mean normal activity in serum) are effectively treated with pharmacological doses of biotin (5–20 mg daily). Biotinidase deficiency is an inherited metabolic disorder that if untreated can result in neurological and cutaneous features. We examined the relationship between biotinidase activity and age at collection to determine how best to identify infants with partial biotinidase deficiency. Methods: Biotinidase activity in dried blood spots is determined using a quantitative fluorometric assay. Subsequent specimens with biotinidase activity ≤100 U were analyzed by mutation analysis to determine the range of activities expressed in infants with partial biotinidase deficiency. A total of 54 specimens had mutation analysis performed identifying 20 affected infants who would not have been identified using the original cutoff activity of 50 U

Methods

Results

Conclusion