Identification of the mutations in BTD gene in Iranian patients with biotinidase deficiency and evaluating their genotype-phenotype correlations.

BACKGROUND

Biotinidase (BTD, encoded by the BTD gene) deficiency is an autosomal recessive neurometabolic disease caused by abnormal BTD activity in the biotin cycle. The clinical symptoms of patients, which are mainly neurocutaneous, range from mild to severe based on the enzyme activity level. This study aimed to identify BTD gene mutations in suspected BTD deficiency patients for the first time in the southwest of Iran and evaluate their genotype-phenotype correlations.

METHODS

11 clinically and biochemically suspected patients from nine unrelated families and their available family members were subjected to Sanger sequencing. Segregation analysis was performed for novel mutation. The effect of each mutation on protein stability and hydropathicity, as well as the pathogenicity prediction of all detected mutations were assessed using various in silico analysis tools.

RESULTS

Six mutations including a novel and five previously reported mutations were identified in patients with different ethnicities. Three out of five known mutations were reported for the first time in Iran. Various common clinical manifestations and a rarely reported coexistence of celiac disease in biotinidase deficiency patients were observed. The novel missense variant c.787G > A (p.Glu263Lys) was detected in exon 4 of the BTD gene, within the biotinidase-like domain of the BTD protein. This variation was found in two cousins of a family, both developed the same initial clinical presentation. In silico analyses revealed that this missense substitution decreased protein stability and increased protein hydrophilicity. Additionally, the known frameshift mutation c.1264delG (p.val422serfster59), was the most frequent allele in the studied population. We also predicted and visualized the effects of the novel and frameshift mutations on protein structure.

CONCLUSION

Our findings expanded the mutational spectrum of the BTD gene and provided valuable data on genotype-phenotype correlations, which helps in genetic counseling. Furthermore, the necessity of performing molecular analysis along with enzymatic analysis was highlighted by this study.