Analysis of CYP2D6 Allele Frequencies and Identification of Novel SNPs and Sequence Variations in Sardinians

The CYP2D6 enzyme is involved in the metabolism of many commonly prescribed drugs. The presence of polymorphisms in the CYP2D6 gene may modulate the enzyme level and activity affecting individual responses, to pharmacological treatment in drug level, response and adverse reactions. Aims. This study aimed to analyze the determination of allele frequencies in Sardinians and the comparison to frequencies found in the Caucasian Population. Methods and Materials. We used a Long PCR strategy coupled to direct genomic DNA sequencing analysis. An amplification allele-specific was carried out to infer the correct allelic phase. The TaqMan Gene Copy Number Assay (Applied Biosystems) was used to verify the presence of gene deletions/multiplications. Results and Conclusions. Our results indicated that CYP2D6 allele frequencies in Sardinians differed from those previously detected in the Caucasian Population. Moreover, three new SNPs and four novel haplotypes were identified. 1. Introduction Cytochrome P450 2D6 (CYP2D6) is a highly polymorphic gene, which is responsible for the metabolism of several key endogenous substrates and other xenobiotics [1] and about 25% of the most commonly prescribed drugs [2–4] (Table 1). More than 130 Single Nucleotide Polymorphisms (SNPs) have been identified within the CYP2D6 gene, including numerous nonsynonymous variations, as well as silent, promoter, and intronic changes. The 82 allelic variants and numerous subvariants reported to date are summarized in the Human CYP Allele Nomenclature Committee website [5]. The presence of SNPs can alter CYP2D6 enzymatic activity with effects ranging considerably within a population and includes individuals with ultrarapid (UM), extensive (EM), intermediate (IM), and poor (PM) metabolizer status. Furthermore, rearrangements within the gene locus have created multiple functional gene copies or deleted the entire gene, resulting in increased or absent drug metabolism, respectively [6, 7]. Genotypic analysis to identify individual polymorphisms has become increasingly important during drug development and for selection of individualized therapies. This analysis aims to increase the number of responders and to limit the incidences of adverse events. Table 1: Class list of major CYP2D6 isoenzyme substrates [ 3, 4]. In our previous work [8], we tried to create a complete genotyping method for the simultaneous analysis of CYP3A4, CYP3A5, CYP2C9, CYP2C19, and CYP2D6 SNPs. The genotyping of the CYP2D6 gene was difficult due to its polymorphic nature, the presence of two flanking pseudogenes, and copy