Does the CG genotype of SRD5A2 rs523349 produce intermediate 5α-reductase activity?

The SRD5A2 rs523349 polymorphism (V89L) is a well-characterized genetic variant that directly influences the activity of the 5α-reductase type 2 enzyme, which is responsible for converting testosterone into the more potent androgen, dihydrotestosterone (DHT). Research consistently supports a clear relationship between specific alleles and enzymatic efficiency.

Mechanistic explanations

The polymorphism involves a substitution at codon 89 of the SRD5A2 gene. The C allele encodes the amino acid valine (V), while the G allele (sometimes referenced as T) encodes leucine (L). This structural change significantly alters the enzyme's catalytic properties:

• High-activity form: The C allele (Valine) is associated with the "wild-type" or high-activity form of the enzyme, facilitating rapid conversion of testosterone to DHT.
• Reduced-activity form: The G allele (Leucine) creates a variant with decreased catalytic efficiency, leading to lower levels of DHT production.
• Gene dosage effect: The presence of these alleles follows a co-dominant pattern where the resulting enzyme activity is proportional to the number of high-activity alleles present.

Clinical and effectiveness evidence

Studies across various populations, including large-scale genomic analyses, have validated the functional impact of these genotypes. Clinical evidence includes:

• Allele-Specific Activity: Individuals with the CC genotype (homozygous Valine) show the highest 5α-reductase activity. Those with the GG genotype (homozygous Leucine) exhibit significantly reduced activity, often measured via lower serum DHT levels or altered androgen markers like sex hormone-binding globulin (SHBG).
• Heterozygous Intermediate Activity: The CG genotype (Val/Leu) consistently results in intermediate enzymatic activity. This "middle-ground" profile means heterozygotes generally produce less DHT than CC individuals but more than GG individuals, effectively modulating the androgenic environment.
• Health Implications: This intermediate activity can influence the risk profile for androgen-dependent conditions. For example, the L allele (G) is associated with a lower risk of benign prostatic hyperplasia (BPH) and potentially modified risks for androgenetic alopecia due to the lower overall DHT exposure compared to the C allele.

Bottom line

The claim is accurately supported by science: the C allele represents high activity (Valine), the G allele represents lower activity (Leucine), and the CG genotype produces an intermediate level of 5α-reductase activity through a classic gene-dosage effect.