rs482843 — CTH

CTH rs482843 — A Placental H₂S Switch and Preeclampsia Risk

Hydrogen sulfide (H₂S) is not just an industrial gas — it is one of the body's own signaling molecules, produced enzymatically in vascular tissue and the placenta to regulate blood flow, suppress inflammation, and protect against hypoxic injury. The enzyme responsible in the cardiovascular system is cystathionine gamma-lyase (CTH, also called CSE)¹¹ cystathionine gamma-lyase (CTH, also called CSE)
encoded by CTH on chromosome 1p31; converts cystathionine to cysteine with H₂S as a byproduct of cysteine catabolism. During pregnancy, CTH-derived H₂S becomes critically important: it dilates placental arteries, counteracts the anti-angiogenic factors that can cause preeclampsia, and promotes the deep placental invasion required for normal fetal growth.

rs482843 is a common intronic variant in CTH (GRCh38 chr1:70,406,697, A>G). Unlike the missense variant rs1021737 (Ser403Ile), rs482843 does not alter the protein sequence. Its functional consequence is regulatory — the intronic position (c.-120+401A>G per Ensembl annotation) likely affects splicing efficiency, transcription factor binding within an intronic regulatory element, or mRNA processing, with net effects on CTH expression levels in placental tissue. The G allele — specifically the GG genotype — carries significantly elevated preeclampsia risk in Caucasian women, while rs1021737 (the coding variant in the same gene) shows no preeclampsia association in the same population.

The Mechanism

Preeclampsia is characterized by inadequate placental vascularization, release of anti-angiogenic factors (sFlt-1 and soluble endoglin), and systemic maternal hypertension after 20 weeks' gestation. The H₂S/CTH system functions as a protective brake²² protective brake
described by Ahmed & Ramma 2015 as an "accelerator-brake" model where loss of endogenous H₂S production removes the protective counter-signal against pathological vascular stress against this process. H₂S generated by CTH in placental trophoblasts and vascular smooth muscle suppresses sFlt-1 and soluble endoglin release, promotes placental growth factor (PlGF) signaling, and maintains endothelial nitric oxide synthase (eNOS) activity — all of which are deficient in preeclampsia.

Experimental work by Ahmed et al. 2017³³ Experimental work by Ahmed et al. 2017
Ahmed A, Rezai H, Broadway-Stringer S. Evidence-Based Revised View of the Pathophysiology of Preeclampsia. Adv Exp Med Biol. 2017. showed that augmenting the H₂S/Cth pathway in mouse preeclampsia models restored placental vasculature and improved fetal growth. If rs482843's G allele reduces CTH expression in placental tissue — even modestly — the protective H₂S signal may be insufficient to prevent the cascade that leads to preeclampsia.

Importantly, this is a placenta-specific phenotype. The same variant shows no significant association with essential hypertension in non-pregnant adults (Li et al. 2008; n=993 Han Chinese adults), suggesting the G allele's effect is conditional on the unique vascular demands of pregnancy, where H₂S production must scale dramatically to accommodate placental blood flow.

The Evidence

The primary association comes from Mrozikiewicz et al. 2015⁴⁴ Mrozikiewicz et al. 2015
The importance of rs1021737 and rs482843 polymorphisms of cystathionine gamma-lyase in the etiology of preeclampsia in the Caucasian population. Ginekol Pol. 2015;86(2):119–25. a case-control study of 60 women with preeclampsia and 120 healthy pregnant controls from a Caucasian Polish population. The GG genotype of rs482843 was significantly more prevalent in preeclampsia cases than controls (p<0.000001), with the G allele itself also reaching genome-wide significance thresholds (p<0.000001). Critically, the companion coding variant rs1021737 showed no significant association with preeclampsia in the same cohort — indicating that rs482843 is the functionally relevant CTH variant for pregnancy-specific vascular dysfunction, while rs1021737 operates through a distinct mechanism relevant to cardiovascular and homocysteine metabolism.

The finding has not yet been replicated in independent large cohorts, and the study size (n=180 total) limits precision. The biological plausibility is strong given the mechanistic data on H₂S in placental biology, but independent replication in diverse populations is needed before this reaches "strong" evidence status.

Practical Actions

For women with the GG genotype who are pregnant or planning pregnancy, the actionable focus is on supporting CTH enzyme output through its cofactor requirements and dietary precursors. CTH is a pyridoxal-5-phosphate (PLP)-dependent enzyme⁵⁵ pyridoxal-5-phosphate (PLP)-dependent enzyme
PLP is the bioactive form of vitamin B6, required for all transsulfuration enzymes including CTH — ensuring optimal B6 status is a direct biochemical support for CTH activity. Providing abundant cysteine precursors (eggs, garlic, onions, cruciferous vegetables) and early prenatal monitoring for preeclampsia signs (blood pressure, proteinuria, placental growth factor levels) are the practical priorities.

Women with the AG genotype have an intermediate picture. The allele-dose effect is consistent with codominant inheritance, and AG carriers warrant prenatal vigilance without the same urgency as GG.

Interactions

rs482843 and rs1021737 are two independent CTH variants with distinct phenotypic profiles — rs482843 is relevant to preeclampsia risk, rs1021737 to homocysteine and cardiovascular disease. A woman carrying GG at rs482843 and TT at rs1021737 would have both H₂S insufficiency during pregnancy and impaired transsulfuration at baseline, creating a compounded vulnerability. Elevated homocysteine from rs1021737 TT is itself a known risk factor for preeclampsia, adding a second mechanistic pathway.

The H₂S system also interacts with eNOS (NOS3): H₂S produced by CTH enhances endothelial nitric oxide availability. Women carrying NOS3 variants with reduced eNOS activity alongside CTH rs482843 GG may face a dual vasodilatory deficit in the placenta.