Two patients with GMPPB mutation: The overlapping phenotypes of limb-girdle myasthenic syndrome and limb-girdle muscular dystrophy dystroglycanopathy.

Authors

Montagnese F1, Klupp E2, Karampinos DC2, Biskup S3, Gläser D4, Kirschke JS2, Schoser B1.
  1. Friedrich-Baur Institut, Department of Neurology, Ludwig-Maximilian University, Ziemssenstrasse 1a, 80336, Munich, Germany.
  2. Section of Diagnostic and Interventional Neuroradiology, Klinikum rechts der Isar, Technische Universität, Munich, Germany.
  3. CeGaT GmbH, Tübingen, Germany.
  4. Genetikum, Neu-Ulm, Germany.

Abstract

INTRODUCTION:

Mutations in the guanosine diphosphate-mannose pyrophosphorylase-B gene (GMPPB) have been identified in congenital muscular dystrophies, limb-girdle muscular dystrophy (LGMD2T), and congenital myasthenic syndromes (CMSs); overall, 41 patients have been described.

METHODS:

Two patients presented with a myasthenic syndrome (patient 1; 74 years old) and rhabdomyolysis (patient 2; 23 years old). Examinations included repetitive nerve stimulation, muscle biopsy and whole-body MRI (WBMRI); next generation sequencing facilitated diagnosis.

RESULTS:

We identified the following GMPPB mutations: c.79G>C/c.859C>T in the 23-year-old man with LGMD2T-phenotype and c.79G>C homozygosity in the 74-year-old woman with CMS phenotype. WBMRI showed fatty degeneration of paraspinal, thigh adductor, and calf muscles in patient 1 and edematous changes of the soleus muscle in patient 2.

CONCLUSIONS:

This case of c.79G>C homozygosity causing a mild, late-onset CMS phenotype, confirms the mild nature of this common mutation. The descriptions of these 2 new GMPPB cases add to the knowledge regarding this recently discovered, heterogeneous disease. Muscle Nerve 56: 334-340, 2017.