rs117896735 — INPP5F

INPP5F and the Protein-Clearance Gateway to REM Sleep Behavior Disorder

REM sleep behavior disorder (RBD)¹¹ REM sleep behavior disorder (RBD)
During RBD, the normal motor paralysis of REM sleep fails, causing people to act out their dreams — punching, kicking, yelling. It is the strongest single predictor of Parkinson's disease and Lewy body dementia: over 80% of those diagnosed with idiopathic RBD eventually convert to a synucleinopathy within 14 years. is no ordinary sleep disturbance. It sits at the far upstream end of the Parkinson's disease continuum — years before motor symptoms emerge and dopamine neurons begin to die. This variant, rs117896735, sits in an intron of the INPP5F gene and emerged from the first major RBD GWAS as one of only five loci reaching genome-wide significance out of the entire human genome.

The locus spans two genes: INPP5F, which encodes an enzyme called Sac2²² Sac2
INPP5F is also known as Sac2 — a member of the SAC phosphatase family that dephosphorylates phosphatidylinositol 4-phosphate on endosomal membranes, and BAG3, a co-chaperone that sits at the intersection of two major protein-disposal systems.

The Mechanism

INPP5F/Sac2 controls the phosphoinositide composition of endosomal membranes. It functions as a PI4P phosphatase³³ PI4P phosphatase
Phosphatidylinositol 4-phosphate is a lipid signal that recruits trafficking proteins to endosomes; its timely removal is required for endosomal cargo sorting and recycling, dephosphorylating PI(4)P in concert with OCRL to regulate endocytic recycling — the same pathway by which alpha-synuclein aggregates are routed toward lysosomal degradation. Disruption of this pathway impairs autophagosome loading and delays clearance of misfolded proteins before they can seed Lewy body formation.

Immediately neighboring INPP5F, BAG3⁴⁴ BAG3
BCL2-associated athanogene 3 — a co-chaperone that bridges Hsp70 and autophagy receptor p62/SQSTM1 to direct misfolded client proteins into autophagosomes rather than the proteasome orchestrates the switch from proteasomal degradation to selective macroautophagy when the proteasome is overwhelmed by misfolded proteins — precisely the scenario in aging neurons accumulating alpha-synuclein. BAG3 forms a trimeric complex with Hsp70 and p62/SQSTM1, colocalizing with autophagy markers in brain tissue. When BAG3 is overexpressed, alpha-synuclein clearance via macroautophagy increases in an Atg5-dependent manner; when BAG3 is reduced, toxic alpha-synuclein accumulates.

rs117896735 is an intronic variant, so it does not alter either protein's coding sequence. It is most likely a regulatory variant⁵⁵ regulatory variant
eQTL studies at this locus did not reach significance in the Krohn 2022 dataset, but the proximity to regulatory elements controlling INPP5F and BAG3 expression in dopaminergic neurons is consistent with the locus's functional effect on protein quality control influencing transcriptional output of INPP5F, BAG3, or both — subtly reducing the brain's capacity to clear misfolded proteins through the endolysosomal-autophagic axis.

The Evidence

The landmark genome-wide association study by Krohn et al. 2022⁶⁶ Krohn et al. 2022
Meta-analysis of iRBD + PD-with-probable-RBD cohorts spanning multiple European and North American sites combined 2,843 RBD cases with 139,636 controls, identifying rs117896735 with an odds ratio of 1.80 (95% CI 1.48–2.19, p=4.70×10⁻⁹). The A allele effect was consistent across the isolated RBD cohort (OR 1.88) and the PD-with-probable-RBD cohort (OR 1.57), supporting genuine association rather than a population-specific artefact. The A allele frequency in the GWAS was approximately 2% — enriched above the gnomAD European frequency of ~1.4% — consistent with a variant under mild purifying selection for its risk effect.

This OR of 1.80 is large by GWAS standards⁷⁷ large by GWAS standards
Common GWAS hits for common diseases typically show OR 1.05–1.20; OR ≥ 1.5 is uncommon for a common variant and suggests meaningful biological impact on the pathway. The four other genome-wide significant RBD loci map to SNCA (alpha-synuclein itself), GBA (lysosomal glucocerebrosidase), TMEM175 (lysosomal K⁺ channel), and SCARB2 (lysosomal membrane protein) — all genes with direct roles in lysosomal protein degradation. The INPP5F/BAG3 locus fits this pattern: upstream phosphoinositide regulation feeding into the same autophagic clearance axis.

On the BAG3 side, Cao et al. 2017⁸⁸ Cao et al. 2017
Cell-based and transgenic mouse study demonstrating BAG3's role in Atg5-dependent selective macroautophagy of alpha-synuclein directly demonstrated that BAG3 modulates alpha-synuclein quality control in dopaminergic neurons. Ying et al. 2022⁹⁹ Ying et al. 2022
Mouse striatal BAG3 overexpression reduced dopaminergic neuron loss and microglial activation following inflammatory challenge extended this to show BAG3 also suppresses NLRP3 inflammasome activation, adding a neuroinflammatory dimension to the locus's relevance.

Practical Implications

The A allele does not cause RBD; it shifts the probability. At OR 1.80 with a baseline population RBD prevalence of roughly 0.5–1%, even A allele carriers face an absolute lifetime risk well below 5% in isolation. However, RBD is itself a prodromal state for synucleinopathies with ~80% conversion rates over 14 years. The practical value of knowing this genotype lies in motivating early surveillance and lifestyle choices that support the protein-clearance pathway that this locus modulates.

The autophagic axis is specifically addressable: sleep architecture itself¹⁰¹⁰ sleep architecture itself
Deep slow-wave sleep drives glymphatic clearance of alpha-synuclein from the brain via the perivascular space; RBD reduces slow-wave sleep independently of its motor symptoms drives the glymphatic clearance of brain alpha-synuclein. Prioritizing sleep quality and continuity is therefore directly relevant to the locus's biology.

Interactions

The INPP5F/BAG3 locus connects to other RBD and Parkinson's risk variants through the shared autophagic-lysosomal clearance pathway. GBA variants (rs76763715, rs34637584) impair lysosomal glucocerebrosidase activity, creating downstream substrate backlog in the same pathway. SNCA variants (rs356182) directly affect alpha-synuclein expression and aggregation propensity. TMEM175 variants (rs34311866) impair lysosomal acidification required for autophagic cargo degradation. Carriers of multiple risk alleles across these loci may carry compounded reductions in protein-clearance capacity — a polygenic load on the same biological axis.