rs34311866 — TMEM175

TMEM175 p.Met393Thr — When the Lysosomal Drain Gets Clogged

Deep inside every cell, lysosomes act as the cell's recycling plant — breaking down old proteins, clearing misfolded aggregates, and recycling the parts. Maintaining the right internal pH (around 4.5–5.0) is essential for the digestive enzymes inside to work. TMEM175 encodes a lysosomal ion channel¹¹ lysosomal ion channel
proton-activated, proton-selective K+/H+ channel that fine-tunes lysosomal acidity — a molecular pressure-relief valve. The rs34311866 C allele introduces a methionine-to-threonine substitution at position 393 that partially disables this valve, with consequences that reach all the way to Parkinson's disease risk.

The Mechanism

The M393T substitution reduces channel current amplitude²² The M393T substitution reduces channel current amplitude compared to wild-type, placing function midway between the functional and knockout states. When the channel cannot adequately regulate lysosomal pH, two downstream failures occur: First, autophagosome clearance is impaired³³ autophagosome clearance is impaired — cellular debris builds up rather than being digested. Second, and most critically for neurodegeneration, alpha-synuclein — the protein that aggregates into Lewy bodies in Parkinson's disease — accumulates in its phosphorylated (aggregation-prone) form. Wild-type TMEM175 overexpression reduces phospho-α-synuclein; M393T overexpression does not. The channel is also considered a druggable target for lysosomal dysfunction in neurodegeneration⁴⁴ druggable target for lysosomal dysfunction in neurodegeneration, with selective inhibitors and activators under active investigation.

The Evidence

The genetic signal is one of the strongest in Parkinson's disease research. Chang et al. 2017 (Nature Genetics) identified the TMEM175 locus with OR 1.23, p=1×10⁻⁵⁰⁵⁵ Chang et al. 2017 (Nature Genetics) identified the TMEM175 locus with OR 1.23, p=1×10⁻⁵⁰ across 26,035 cases and 403,190 controls — one of 17 novel PD risk loci. The Nalls et al. 2019 Lancet Neurology meta-analysis of 37,688 cases and 1.4 million controls⁶⁶ Nalls et al. 2019 Lancet Neurology meta-analysis of 37,688 cases and 1.4 million controls confirmed the locus among 90 independent genome-wide significant signals. Functional studies by Wie et al. (Nature, 2021) quantified the C allele OR at 1.26 [95% CI 1.22–1.31]⁷⁷ Wie et al. (Nature, 2021) quantified the C allele OR at 1.26 [95% CI 1.22–1.31] and found that C carriers in the University of Pennsylvania and PPMI cohorts showed faster motor decline (p=0.032) and faster cognitive decline (p=0.005) after diagnosis. Beyond PD, the Blauwendraat et al. 2019 age-at-onset GWAS⁸⁸ Blauwendraat et al. 2019 age-at-onset GWAS (28,568 cases) found rs34311866 p.M393T is the primary coding signal for earlier PD onset. The Krohn et al. 2022 RBD GWAS (Nature Communications)⁹⁹ Krohn et al. 2022 RBD GWAS (Nature Communications) then identified TMEM175 as one of five loci for REM sleep behavior disorder — a prodromal synucleinopathy — shared across RBD, PD, and dementia with Lewy bodies.

Practical Actions

Carriers of the C allele cannot fix the M393T variant, but they can support the cellular processes that compensate for reduced lysosomal function. The principal strategy is maintaining autophagic flux — the rate at which cells clear protein waste — through targeted supplementation and lifestyle choices. Trehalose, a disaccharide that activates the TFEB transcription factor independently of mTOR, has documented preclinical effects on TMEM175-dependent clearance pathways. Spermidine similarly induces autophagy via eIF5A hypusination. Urolithin A (a gut metabolite of ellagic acid) activates mitophagy and has Phase II trial data in humans. These are not generic supplements — they specifically address the autophagy-lysosomal axis impaired by M393T. Neurological monitoring for early-onset cognitive or motor changes is warranted, particularly given evidence of accelerated decline after diagnosis.

Interactions

TMEM175 sits in the same autophagy-lysosomal pathway¹⁰¹⁰ autophagy-lysosomal pathway as GBA1 (glucocerebrosidase) — the strongest known genetic risk factor for PD (rs76763715, N370S). Both genes affect lysosomal function and alpha-synuclein clearance, but through distinct mechanisms: TMEM175 at the pH-regulation step, GBA1 at the enzymatic glucosphingolipid-hydrolysis step. Carriers of risk alleles in both genes may face compounded impairment of lysosomal alpha-synuclein clearance. rs2736990 (SNCA intron 4) increases alpha-synuclein expression levels — a separate upstream contributor to the same aggregation cascade. The combination of elevated substrate (SNCA) and impaired clearance (TMEM175) represents a convergent risk architecture worth capturing as a compound interaction candidate.