Is the IRS1 rs2943641 CC genotype associated with reduced insulin sensitivity and impaired insulin signaling?

At age 53, the rs2943641 genotype may be relevant as one contributor to insulin-resistance risk, but it does not by itself establish an individual’s metabolic status or treatment needs.

Clinical/metabolic evidence

• The overall claim is substantially supported for insulin sensitivity: the IRS1 rs2943641 C allele is consistently associated with higher fasting insulin, higher HOMA-IR, and hyperinsulinemia. CC homozygosity therefore marks relatively lower insulin sensitivity than T-containing genotypes.
• In one cohort, T-allele carriers had a 13.3% lower insulin area under the curve than CC homozygotes, directionally supporting greater insulin resistance in CC individuals.
• These associations are based mainly on fasting measures, HOMA-IR, and oral-glucose-tolerance testing rather than euglycemic clamp measurements. The precise magnitude of insulin-sensitivity reduction attributable to CC status is therefore not established.

Mechanistic evidence

• Human skeletal-muscle biopsy data provide a biologically coherent explanation: C-allele carriers had lower basal IRS1 protein and reduced insulin-stimulated IRS1-associated PI3K activity.
• IRS1–PI3K signaling is a proximal post-receptor insulin-signaling pathway; reduced IRS1 abundance and PI3K activation are compatible with weaker cellular insulin responses.
• However, these functional findings were reported for C-allele carriage, not specifically as CC-versus-CT/TT comparisons. Direct downstream evidence in CC carriers—such as AKT phosphorylation, glucose transport, or muscle glucose uptake—has not been demonstrated. Because rs2943641 is intergenic and approximately 500 kb from IRS1, the findings do not prove that this variant directly alters IRS1 transcription or function.

Bottom line

• CC genotype is a moderately supported marker of relatively reduced insulin sensitivity, with plausible but incompletely genotype-specific evidence of impaired IRS1–PI3K insulin signaling. Its clinical relevance is best interpreted alongside measured glycemia, insulin-resistance indices, adiposity, and other cardiometabolic risk factors.