Arrhythmogenic Cardiomyopathy
Gene: GNPTAB
GNPTAB encodes the α and β subunits of N-acetylglucosamine-1-phosphotransferase. Biallelic variants in GNPTAB cause mucolipidosis (ML), a lysosomal storage disorder arising due to the impaired transport of lysosomal enzymes, resulting in the aberrant secretion of lysosomal enzymes into the extracellular space and accumulation of undigested molecules within the lysosome.
ML II is a severe paediatric disorder typically resulting in death due to cardiorespiratory failure, caused by biallelic GNPTAB loss-of-function. The severity of disease is thought to correlate with the degree of disruption of protein function. Patients with ML IIIα/β typically carry one loss-of-function and one hypomorphic allele, resulting in an attenuated clinical phenotype with some residual enzymatic activity. Commonly observed features of ML IIIα/β include carpal tunnel syndrome, joint stiffness and pain, gait disturbance, short stature, or coarse facial features.
Review of the literature suggest that patients with ML IIIα/β can present with an adult-onset primary or isolated cardiomyopathy. There are at least six independent reports of patients with ML IIIα/β developing a primary cardiac presentation, with features consistent with both arrhythmogenic and dilated cardiomyopathy. In some cases, extracardiac features are subtle or absent, supporting the inclusion of GNPTAB on clinical cardiomyopathy panels.
1. Stewart et al. (2026) reported a sibling-pair with compound heterozygous variants in GNPTAB (c.3503_3504del, p.(Leu1168GlnfsTer5); c.1400A>G, p.(Asp467Gly)). The proband had a history of gait disturbance and learning difficulties, with skeletal features indicative of dysplastic processes. However, his primary presentation was a sudden cardiac death (SCD) due to a presumed cardiac arrhythmia at 31 years of age with left ventricular fibrosis observed during autopsy. Following the SCD, the proband’s sister presented for cardiac screening with a dilated right ventricle, multiple episodes of polymorphic ventricular tachycardia and non-ischemic global scarring of the left ventricle. PMID: 42227110.
2. Castrichini et al. (2026) reported a 38-year-old patient with a primary presentation of arrhythmogenic left ventricular cardiomyopathy with near-circumferential ring-like subepicardial late gadolinium enhancement (LGE). The patient carried compound heterozygous variants in GNPTAB (c.2502del, p.(Lys834AsnfsTer5), c.771G>A, p.(Leu257Leu)) and had subtle extracardiac features including coarse facial features, corneal clouding and cataracts. DOI: 10.1016/j.hrcr.2026.06.016.
3. Wu et al. (2026) reported a patient with early cardiomyopathy who underwent genetic testing due to suspicion of Fabry disease. The patient was diagnosed with ML IIIα/β after genetic testing revealed compound heterozygous variants in GNPTAB (c.2715+1G>A; c.1702T>G, p.(Phe568Val)) with elevated plasma lysosomal enzyme levels. The patient displayed no hallmark skeletal features of ML IIIα/β. DOI: 10.1093/eurheartj/ehag233.
4. Kashihara et al. (2020) reported a 44-year-old patient with ML IIIα/β and right ventricular dilatation and dysfunction. Extended LGE was present in the right ventricle free wall, and linear LGE was observed in the subepicardial wall of the interventricular septum and the left ventricle. Hallmark features of ML IIIα/β such as a coarse face, short stature, stiff fingers, and restricted joint mobility were reported from childhood. The patient carried compound heterozygous variants in GNPTAB (c.1120T>C, p.(Phe374Leu); c.3565C>T, p.(Arg1189Ter)). PMID: 32818557.
5. Kwak et al. (2018) reported a 32-year-old patient who presented with a sudden cardiac arrest due to ventricular fibrillation having been diagnosed with dilated cardiomyopathy two years earlier. Following transplant, analysis of her explanted heart showed severe bilateral ventricular dilatation with interstitial fibrosis. The patient displayed features of skeletal dysplasia and was diagnosed with ML IIIα/β following genetic testing which revealed compound heterozygous variants in GNPTAB (c.2715+1G>A; c.3173C>G, p.(Ser1058Ter)). PMID: 30610051.
6. Steet et al. (2005) reported a 47-year-old patient who presented with dilated cardiomyopathy and mild neuropathy. She was diagnosed with ML IIIα/β following genetic and lysosomal enzyme testing and carried the homozygous c.771G>A, p.(Leu257Leu) variant. PMID: 15633164.
Sources: LiteratureCreated: 23 Sep 2026, 8:49 a.m.
Mode of inheritance
BIALLELIC, autosomal or pseudoautosomal
Phenotypes
Arrhythmogenic Cardiomyopathy; Dilated Cardiomyopathy; Mucolipidosis type IIIα/β; Mucolipidosis type II
Publications
gene: GNPTAB was added gene: GNPTAB was added to Arrhythmogenic Cardiomyopathy. Sources: Literature Mode of inheritance for gene: GNPTAB was set to BIALLELIC, autosomal or pseudoautosomal Publications for gene: GNPTAB were set to 42227110, 32818557, 30610051, 15633164 Phenotypes for gene: GNPTAB were set to Arrhythmogenic Cardiomyopathy; Dilated Cardiomyopathy; Mucolipidosis type IIIα/β; Mucolipidosis type II Review for gene: GNPTAB was set to GREEN