Page 91 - Basic _ Clinical Pharmacology ( PDFDrive )

CHAPTER 5 Pharmacogenomics 77

TABLE 5–1 Major alleles and frequencies in African, Asian, and European populations. (Continued)

Fraction Fraction Fraction in
in African in Asian European
1
Gene Allele(s) dbSNP Number Amino Acid Function Activity Populations Populations Populations
G6PD
B Reference — Normal IV — — —
A rs1050829 N126D Normal III–IV 0.31–0.35 0.00 0.00–0.060
A- (rs1050829, rs1050828) (N126D, V68M) Decreased III 0.00–0.30 n/a n/a
A- (rs1050829, rs137852328) (N126D, R227L) (5–10%)
A- (rs1050829, rs76723693) (N126D, L323P)
Mediterranean (rs5030868) S188P Decreased II 0.00–0.052 0.00–0.31 0.00–0.074
(< 1%)
Canton (rs72554665), Kaiping R459L/R463H Decreased II
Mahidol G163S Decreased III
(5–32%)
Chinese-5, Gaohe L342F Decreased III
H32R
SLCO1B1
*1a Reference — Normal — 0.17 0.27 0.50
*1b rs2306283 N130D Normal — 0.78 0.60 0.22
*5 rs4149056 V174A Decreased — 0.00 0.00 0.01
*15, *17 rs4149056, others V174A others Decreased — 0.03 0.13 0.14
HLA-B
*57:01 — — positive — 0.010 0.016 0.068
IFNL3
TT/CT Reference — Unfavorable — — — —
CC rs12979860 — Favorable — 0.39 0.87 0.63
CYP2C9
*1 Reference — Normal —
*2 rs1799853 R144C Decreased — 0.03 0.00 0.13
*3 rs1057910 I359L Decreased — 0.02 0.04 0.07
VKORC1
–1639G Reference — Normal —
–1639A rs9923231 Reduced Decreased — 0.11 0.91 0.39
expression
1 The Single Nucleotide Polymorphism Database (dbSNP) is an online public repository of genomic variation established by the National Center for Biotechnology Information
(NCBI), https://www.ncbi.nlm.nih.gov/SNP/.

a frequency of approximately 20% in Europeans and is nearly Asian populations, suggesting that this mutation likely took place
absent (< 1%) in Asians (Table 5–1). Based on Hardy-Weinberg prior to the separation of the three major races more than 100,000
principles (see Glossary), the percentage of Europeans who are years ago. Clinically, since some genotyping platforms are specific
homozygous for the CYP2D6*4 allele, ie, who carry the *4 allele to a single ethnicity, it is important to ensure alleles applicable
on both maternal and paternal chromosomes, would be 4%, to the patient population being treated are tested. Of note, rare
whereas that of those who are heterozygotes would be 32%. This or previously undiscovered variants are typically not included in
parallels the lower number of PMs (defined as having two non- commercial tests, and thus novel or rare polymorphisms, which
functional alleles, eg, PMs are homozygous for *3, *4, *5, *6, or may exhibit altered function, will be missed.
any combination of nonfunctional alleles such as *4/*5 ), observed Example: Codeine is a phenanthrene derivative prodrug opi-
in Asian populations (∼1%) compared with European populations oid analgesic indicated for the management of mild to moderately
(∼5–10%) (Table 5–1). In contrast, the *5 gene deletion is found severe pain (Chapter 31). Codeine, like its active metabolite
at similar frequencies (∼3–5%) across European, African, and morphine, binds to μ-opioid receptors in the central nervous