Do common LDLR variants rs2228671 and rs688 increase LDL cholesterol by reducing LDLR-mediated clearance?

The Low-Density Lipoprotein Receptor (LDLR) plays a critical role in maintaining cholesterol homeostasis by clearing LDL particles from circulation. Common genetic variants within the LDLR gene can influence the efficiency of this process, leading to variations in plasma lipid profiles and subsequent cardiovascular risk.

Clinical evidence and cholesterol levels

Research indicates that the rs688 (C>T) variant is a significant modulator of LDL cholesterol (LDL-C) levels. In human cohorts and liver sample studies, the T allele—particularly the TT genotype—is associated with significantly higher total and LDL cholesterol. This effect has been observed to be especially pronounced in women, though it impacts the lipid profiles of both sexes. Conversely, the rs2228671 variant presents a more complex clinical picture. While it is strongly linked to LDL-C levels, several large-scale studies suggest that the minor T allele of rs2228671 is actually associated with lower LDL-C and a reduced risk of coronary heart disease, which contradicts the direction of the claim regarding elevated levels for this specific variant.

Mechanistic explanations

The primary mechanism linking these variants to cholesterol levels involves altered receptor availability and splicing efficiency:

• Splicing Disruption (rs688): The rs688 variant disrupts an exonic splicing enhancer (ESE) in exon 12 of the LDLR gene. This disruption impairs the inclusion of exon 12 during pre-mRNA splicing, leading to increased production of dysfunctional isoforms or mRNA that undergoes nonsense-mediated decay (NMD).
• Reduced Receptor Clearance: The resulting decrease in functional LDLR protein on the hepatocyte surface directly reduces the liver's capacity to clear LDL particles from the blood. This reduction in receptor-mediated clearance is the established molecular pathway leading to elevated circulating LDL-C.
• Linkage and Variation: While rs688 and rs2228671 are sometimes discussed together due to their proximity, they appear to have distinct or even opposing functional impacts. The mechanism for rs688 is well-defined as a loss-of-function effect via splicing, whereas the protective nature of rs2228671 suggests a different, potentially gain-of-function or distinct regulatory influence on LDL clearance.

Bottom line

The claim is partially supported: the rs688 variant is robustly linked to reduced LDL receptor splicing and impaired clearance, leading to higher LDL-C levels. However, the rs2228671 variant is more frequently associated with lower LDL-C levels in clinical literature, suggesting that these common variants do not uniformly contribute to reduced clearance and elevated cholesterol.