EMD (Emerin) — Emery-Dreifuss Muscular Dystrophy
Details
EMD (Xq28) encodes emerin, an inner nuclear membrane protein that also localises to cardiac desmosomes and fasciae adherentes. Inheritance is X-linked recessive. EMD mutations cause Emery-Dreifuss muscular dystrophy (EDMD), in which the cardiac phenotype is the part that kills: atrial electrical disease progressing to atrial standstill, with complete AV block and pacemaker dependency.
EMD and LMNA encode interacting proteins of the same nuclear envelope and produce overlapping skeletal phenotypes, but their cardiac phenotypes diverge sharply — and that divergence determines device selection. (sources/atrial-standstill-hrs-2026, rating: medium)
Key Facts
Cardiac Natural History
- Sequence: sinus rhythm → low P-wave amplitude and PR prolongation → AF/flutter (61%) → atrial standstill → complete AV block → pacemaker dependency (100%). (sources/atrial-standstill-hrs-2026, rating: medium)
- Atrial standstill in 46.7% of EMD carriers (14 of 30) — against 0 of 15 LMNA carriers (P=.001) in the same cohort. (sources/atrial-standstill-hrs-2026)
- Of EDMD patients who develop AF/flutter, 45% progress to atrial standstill, and 28% of the whole EDMD cohort reached standstill. (sources/atrial-standstill-hrs-2026)
- EMD accounts for 33% of all reported atrial standstill cases, and AS has been called "virtually characteristic" of EDMD. (sources/atrial-standstill-hrs-2026)
- Stroke risk is high and premature — 22% thromboembolic events, with disabling strokes before age 45. This is one of the etiologies for which anticoagulation is recommended regardless of conventional risk scores. (sources/atrial-standstill-hrs-2026)
Ventricular Arrhythmia Is Comparatively Uncommon
- Non-sustained VT/VT in 6.7% (2 of 30) versus 60% in LMNA; ICD implantation in 3.3% (1 of 30) versus 60% in LMNA — both P<.001. (sources/atrial-standstill-hrs-2026, rating: medium)
- These estimates rest on 30 patients, so the confidence intervals are wide, and the low event rate is the least secure finding in the cohort.
- Exception: emerinopathy with concomitant left ventricular noncompaction can produce ventricular fibrillation, and in EDMD with LVNC or LVEF ≤35% ICD candidacy should follow standard cardiomyopathy guidelines. (sources/atrial-standstill-hrs-2026)
Device Strategy
- Pacemaker is the default — 76.7% implantation rate. For EMD carriers without LV dysfunction, LVNC or documented ventricular arrhythmia, a pacemaker rather than an ICD is advised. (sources/atrial-standstill-hrs-2026, rating: medium)
- Once pacing is required, the mode question is the same as for any atrial standstill: VVI if there is no capturable atrial tissue, EAM-guided DDD if a viable atrial island can be found.
Genetics and Family Screening
- X-linked recessive: sons of a carrier female have a 50% risk; all daughters of an affected male are obligate carriers.
- Carrier females are not simply unaffected — they may develop cardiac conduction disease and atrial arrhythmias, typically later onset and milder than affected males. They require annual ECG and Holter with echo every 1–2 years. (sources/atrial-standstill-hrs-2026)
- gnomAD LOEUF 0.31 — strongly constrained, consistent with high pathogenicity of loss of function. (sources/atrial-standstill-hrs-2026)
- Cardiac involvement can be life threatening even when skeletal muscle disease is mild, mandating independent cardiac surveillance regardless of neurological severity (2017 AHA scientific statement). Skeletal muscle examination is part of the workup of unexplained atrial standstill for exactly this reason.
Contradictions / Open Questions
- How often LMNA causes atrial standstill is genuinely unresolved. The largest head-to-head cohort found 0 of 15 in LMNA, yet AS in LMNA carriers is reported elsewhere and is listed among laminopathy mechanisms in some reviews. The discrepancy matters directly: if AS is characteristic of emerinopathy and exceptional in laminopathy, family counselling and device planning differ completely between the two genes. (sources/atrial-standstill-hrs-2026, rating: medium)
- The "33% of all reported AS cases" figure is a literature-derived proportion, not a population estimate. It counts what was published, in an era before LMNA testing existed, so it likely overstates EMD and understates other causes.
- ICD thresholds in EMD are extrapolated. The recommendation of pacemaker over ICD rests on a 6.7% ventricular arrhythmia rate in 30 patients — a sample small enough that the true rate could be several-fold higher. No EMD-specific risk model exists.
- Whether early pacemaker implantation, before symptoms, alters outcome is unknown. Pacemaker dependency is 100%, but the timing of implantation is not evidence-based.
- Female carrier penetrance is under-characterised — surveillance intervals are consensus rather than data-driven.
Connections
- The gene it is always compared with: entities/LMNA — same nuclear envelope, opposite cardiac phenotype
- The syndrome it causes: concepts/Atrial-Standstill — AS as the defining cardiac lesion of EDMD
- The parent spectrum: concepts/Atrial-Cardiomyopathy — fibro-fatty replacement, EHRAS class III (IVf)
- Device planning: concepts/Permanent-Pacing-Indications · entities/ICD
- Family management: concepts/Cascade-Family-Screening — X-linked inheritance, obligate carrier daughters
- The overlap phenotype: entities/NDLVC — LV noncompaction with emerinopathy carries ventricular fibrillation risk
- Genetic testing context: concepts/Genetic-Testing-in-Cardiomyopathy