Oxford nanopore sequencing-based assay for BTD gene screening: Design, clinical validation, and variant frequency assessment in the Turkish population

Biotinidase deficiency (BTD) is an autosomal recessive disorder characterized by impaired recycling of the water-soluble vitamin biotin which leads to a spectrum of clinical manifestations ranging from mild to severe, including mainly neurological and cutaneous symptoms. Biotin supplementation is a cornerstone of treatment, but diagnosis often relies on measuring serum enzyme activity, which needs to be confirmed by genetic analysis. Thus, molecular methods become necessary in the differential diagnosis of BTD. Accordingly, countries with a high-incidence have implemented next-generation sequencing (NGS) techniques to newborn screening programs for BT. Nevertheless, NGS platforms, while well-established, present challenges in cost, labor, accessibility, and duration for newborn screening programs targeting BTD, therefore these limitations necessitate the exploration of alternative systems to ensure efficient and widespread screening. Here, third-generation sequencing platforms, notably Oxford Nanopore Technology (ONT), present promising solutions to the associated challenges. Hence, in the present study, we aimed to develop an ONT-based assay for the screening of BTD gene. After designing and optimizing primers for long-PCR using reference DNA, we assessed the performance of the ONT assay in BTD patients previously diagnosed by enzyme assay and confirmed using Illumina-based sequencing. The results demonstrate a strong correlation between the two methods, indicating the reliability of the ONT-based assay. Moreover, this first in-house single gene testing specifically tailored for BTD successfully detected previously known genetic variants with high sequencing depths, affirming the effectiveness of ONT-based sequencing in human genetics.