Retrospective evaluation of patients diagnosed with biotinidase deficiency through the neonatal screening program

Background: Biotin is a water-soluble vitamin found in several nutrients. Biotin binds to proteins and is released by the enzyme named biotinidase when necessary. Free biotin combines with apocarboxylases by means of holocarboxylase synthetase to form holocarboxylases, and acts as a cofactor of these enzymes. Free biotin and lysine are reformed from biocytin by biotinidase. Biotinidase deficiency is an autosomal recessive metabolic disease caused by a defect in the BTD gene located in 3p25.1. Aim: The aim of this study is to evaluate the genotype-phenotype relationship in patients diagnosed with biotinidase deficiency through the neonatal screening program at Dokuz Eylül University Faculty of Medicine, Department of Pediatrics, Pediatric Nutrition and Metabolism Division. Materials and Methods: The study was conducted at Dokuz Eylül University Faculty of Medicine, Department of Pediatrics, Pediatric Nutrition and Metabolism Division. Charts of patients referred with a provisional diagnosis of biotinidase deficiency by the neonatal screening program and diagnosed with biotinidase deficiency were evaluated retrospectively. Eighty-three cases were enrolled in the study. Demographic data (age, sex, parental consanguinity), age at the time of diagnosis, age at the onset of treatment, follow-up period, treatment and doses were documented. Biotinidase enzyme activity levels at the time of admission, highest and lowest biotinidase enzyme activity levels in the follow-up period, and BTD gene mutation analyzes were recorded. SPSS 23.0 program was used for statistical analysis. Results: Forty-one (49.4%) of the patients were female and 42 (50.6%) were male. The median age of the patients was 11 days (5-46). Of the 83 patients included in the study, 62 (74.7%) had no parental consanguinity, while 21 (25.3%) had consanguinity between their parents. Biotinidase deficiency (BTD) gene (OMIM 253260) analysis was performed in all cases. Twenty-six cases (31.3%) had homozygous mutations and fifty-seven cases (68.7%) had compound heterozygous mutations. When BTD gene analysis results were examined, the most common mutations were c.1330G>C (p.D444H) (87; 52.4%), c.470G>A (p.R157H) (25; 15.1%) and c 98-104delinsTCC (p.C33fs) (17; 10.2%). One of the patients had a previously identified possible pathogenic variation of c.625C>T (p.R209C). When the cases were stratified into 3 groups according to their p.D444H mutation status in BTD gene, 20 (24.3%) had homozygous p.D444H mutations, 48 (57.8%) had compound heterozygote mutation with p.D444H and another mutation, and 15 (17.9%) had p.D444H-free mutations. When the level of biotinidase enzyme deficiency was examined in these three patient groups, ten (52.6%) of the twenty-two cases (52.6%) with severe enzyme deficiency were found to have no p.D444H. mutation. In addition, all thirteen cases with heterogeneous enzyme deficiency had either homozygous p.D444H mutation or heterozygous mutations containing p.D444H. Thirty-three (64.7%) of the fifty cases with partial enzyme deficiency had compound heterozygous mutations containing p.D444H. There was a statistically significant negative correlation between p.D444H mutation and enzyme deficiency level. In our hospital, the mother, father and siblings born before 2008 of the cases diagnosed through the neonatal screening are also routinely screened for biotinidase deficiency. As a result of family screening, biotinidase deficiency was detected in the mother in 6 cases, the father in 1, and in one sister and two sisters in 2 cases. Conclusion: Although screening studies have allowed early diagnosis and treatment, thereby preventing emergence of phenotypic findings, our study demonstrated a genotypic-phenotype relationship. The neonatal screening program has been shown to be one of the most effective screening programs, and prevents symptoms. The screening program has also been shown to be useful for diagnosing asymptomatic mothers, fathers and siblings of diagnosed cases. Biotin treatment at a dose of 10-20mg has been shown to be safe and sufficient. Keywords: Biotinidase deficiency, neonatal screening