Molecular diagnosis of hereditary inclusion body myopathy by linkage analysis and identification of a novel splice site mutation in GNE

Abstract

BackgroundMany myopathies share clinical features in common, and diagnosis often requires genetic testing. We ascertained a family in which five siblings presented with distal muscle weakness of unknown etiology.MethodsWe performed high-density genomewide linkage analysis and mutation screening of candidate genes to identify the genetic defect in the family. Preserved clinical biopsy material was reviewed to confirm the diagnosis, and reverse transcriptase PCR was used to determine the molecular effect of a splice site mutation.ResultsThe linkage scan excluded the majority of known myopathy genes, but one linkage peak included the gene GNE, in which mutations cause autosomal recessive hereditary inclusion body myopathy type 2 (HIBM2). Muscle biopsy tissue from a patient showed myopathic features, including small basophilic fibers with vacuoles. Sequence analysis of GNE revealed affected individuals were compound heterozygous for a novel mutation in the 5' splice donor site of intron 10 (c.1816+5G>A) and a previously reported missense mutation (c.2086G>A, p.V696M), confirming the diagnosis as HIBM2. The splice site mutation correlated with exclusion of exon 10 from the transcript, which is predicted to produce an in-frame deletion (p.G545_D605del) of 61 amino acids in the kinase domain of the GNE protein. The father of the proband was heterozygous for the splice site mutation and exhibited mild distal weakness late in life.ConclusionsOur study expands on the extensive allelic heterogeneity of HIBM2 and demonstrates the value of linkage analysis in resolving ambiguous clinical findings to achieve a molecular diagnosis.

Phenotypic stratification and genotype–phenotype correlation in a heterogeneous, international cohort of GNE myopathy patients: First report from the GNE myopathy Disease Monitoring Program, registry portion

“…The presented timeline of the disease milestones confirms the slow, but progressive course and a noticeable variability between patients even with the same genotype [8] , [9] , [23] , [24] .…”

GNE Myopathy: Etiology, Diagnosis, and Therapeutic Challenges

“…The age of onset and the severity of the disease may vary significantly [10,13], even among siblings [15][16][17]. The factors that affect progression are not well understood, but genetic modifiers and environmental factors are thought to play a role.…”

GNE myopathy: current update and future therapy

“…Clinically, the diagnosis may be confused with other conditions, such as other distal myopathies, limb girdle muscular dystrophy,23 spinal muscular atrophy or Charcot-Marie-Tooth disease. The reliability of muscle biopsy for the diagnosis of GNE myopathy appears to depend on the technical skill and diagnostic expertise of those handling and evaluating the specimen (see above).…”