A novel mutation in HINT1 gene causes autosomal recessive axonal neuropathy with neuromyotonia, effective treatment with carbamazepine and review of the literature.

INTRODUCTION

Autosomal recessive axonal neuropathy with neuromyotonia (ARAN-NM) is a rare disease entity linked to mutations in the histidine triad nucleotide binding protein 1 (HINT1) gene. The diagnosis and treatment of ARAN-NM are challenging. There have been few reports of ARAN-NM in East Asia.

METHODS

A 15-year-old Chinese ARAN-NM patient developed muscle weakness, cramps and atrophy in the lower limbs at the age of 12. Electromyography (EMG) showed motor axonal degeneration and neuromyotonic discharges. Whole exome sequencing was performed. Bioinformatic methods and computational 3D structure modeling were used to analyze the identified variant. According to literature review, carbamazepine was prescribed to the patient.

RESULTS

Genetic tests identified a homozygous mutation c.356G > T (p.R119L) in the HINT1 gene, which has never been reported before according to HGMD database. Several bioinformatic approaches predicted the variant was damaging. Computational 3D modeling indicated the variant changed the structure of HINT1 protein. Notably, we demonstrated the positive effects of carbamazepine in treating muscle stiffness and cramps of ARAN-NM.

DISCUSSION: 22 variants have been reported in the HINT1 gene, and we identified a novel c.356G > T (p.R119L) variant. Our study expands the genetic spectrum of ARAN-NM. Moreover, large clinical trials are required to further demonstrate the role of carbamazepine in ARAN-NM.