A Comprehensive Study of BTD: Total Reported Variants, In-silico Analyses and Overview of Functional Studies

BTD encodes the biotinidase enzyme, responsible for recycling and maintaining biotin homeostasis in the human body. Biotin is a water-soluble micronutrient essential for various metabolic processes, with most being recycled by the biotinidase enzyme under normal physiological conditions. The process involves Holocarboxylase synthetase covalently attaching free biotin to Apocarboxylases, such as pyruvate carboxylase, 3-methylcrotonyl-CoA carboxylase, propionyl-CoA carboxylase, and acetyl-CoA carboxylase, forming active Holocarboxylases. These active forms are then proteolyzed into biocytin and/or biotin peptides, which are subsequently cleaved by biotinidase enzyme, thus completing the biotin recycling loop. Variants within BTD disrupt the catalytic activity of biotinidase, leading to an inability to recycle biotin. Biotinidase deficiency, an autosomal recessive inherited metabolic disorder, can result from this disruption, causing the accumulation of biotin metabolites and subsequent damage to the peripheral and central nervous systems. The objective of this study was to analyze BTD variants and assess their structural, functional, and clinical significance in biotinidase deficiency. This study presents a comprehensive analysis of BTD variants, identifying a total of 740 reported variants, with exon 4 being a significant hotspot with 452 variants, indicating its potential importance for future genetic screening and diagnostic strategies. The research further provides an in-silico analysis of the BTD proteins, detailing their pathogenicity, domain structure, conserved regions, and key amino acids involved in interaction and structural integrity. Functional studies utilizing animal models demonstrate that BTD knockout adversely affects physiological features and metabolic pathways, with these effects being reversible upon biotin supplementation.