Can low iron stores and the BTBD9 rs3923809 AG genotype increase restless legs symptoms and related sleep movements?

Low iron availability and BTBD9 variation are both relevant to restless legs syndrome (RLS) biology, but they serve different clinical roles: iron status is potentially modifiable, whereas rs3923809 indicates modest susceptibility rather than diagnosis or a deterministic cause.

Clinical and genetic evidence

• Lower ferritin has correlated with greater RLS severity and poorer sleep efficiency in clinical cohorts; in an early study, nearly all people with severe RLS had ferritin ≤50 µg/L. However, three larger population-based studies found no ferritin–RLS association, so ferritin does not reliably predict an individual’s symptom burden.
• The BTBD9 rs3923809 locus is associated with RLS at the allele/locus level. European studies reported risk-allele odds ratios of 1.5–1.8, and a Czech–Austrian–Finnish study reported OR 1.58 (95% CI 1.28–1.96). In a Korean study, AG/AA versus GG was associated with RLS (OR 1.88, 95% CI 1.39–2.56); AG alone was not separately estimated.
• Evidence is stronger for periodic limb movements during sleep (PLMS): A-allele carriage was associated with PLMI ≥15/hour (adjusted OR 1.65), and each A allele with OR 1.43 (95% CI 1.26–1.63). Thus, AG—one A allele—is consistent with increased PLMS susceptibility, though its exact AG-versus-GG risk is unknown.

Mechanistic and practical interpretation

• Regional brain iron deficiency may impair blood–brain-barrier iron transport and iron-dependent dopamine, adenosine, and glutamate signaling. BTBD9 has proposed roles in cellular iron regulation and dopaminergic sleep-motor phenotypes, but rs3923809’s functional effect in human neural tissue is unproven.
• Ferritin should be interpreted with transferrin saturation and clinical context, particularly because inflammation can elevate ferritin despite limited available iron. Genotype does not diagnose RLS or periodic limb movement disorder.

Bottom line

• Low iron stores are a clinically relevant potential contributor to worse RLS symptoms, while rs3923809 AG supports susceptibility—especially to PLMS—but neither ferritin nor genotype alone establishes symptom severity or diagnosis.