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

Boyden SE, Duncan AR, Estrella EA, Lidov HG, Mahoney LJ, Katz JS, Kunkel LM, Kang PB - BMC Med. Genet. (2011)

Bottom Line: 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 father of the proband was heterozygous for the splice site mutation and exhibited mild distal weakness late in life.Our 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.

View Article: PubMed Central - HTML - PubMed

Affiliation: Division of Genetics, Children's Hospital Boston, Boston, MA 02115, USA.

ABSTRACT

Background: Many 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.

Methods: We 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.

Results: The 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.

Conclusions: Our 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.

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Related in: MedlinePlus

Pedigree. Subjects with DNA samples available and tested are labeled with their identification number. Black-filled symbols represent individuals affected with HIBM2, with onset in their 20s or 30s. Tested patients were compound heterozygous with genotype NM_005476.5: c.[1816+5G>A]+[2086G>A]. The gray-filled symbol represents an individual presenting in his 70s with mild HIBM-like symptoms, with genotype NM_005476.5: c.[1816+5G>A]+[=]. Arrow indicates the proband.
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Figure 1: Pedigree. Subjects with DNA samples available and tested are labeled with their identification number. Black-filled symbols represent individuals affected with HIBM2, with onset in their 20s or 30s. Tested patients were compound heterozygous with genotype NM_005476.5: c.[1816+5G>A]+[2086G>A]. The gray-filled symbol represents an individual presenting in his 70s with mild HIBM-like symptoms, with genotype NM_005476.5: c.[1816+5G>A]+[=]. Arrow indicates the proband.

Mentions: The family consisted of five affected siblings, two unaffected siblings, their unaffected mother, and their father, who had mild distal weakness noted late in life (Figure 1). The female proband presented at age 37 with weakness, fatigue while walking, and difficulty walking and climbing stairs. Her weakness was predominantly in the distal lower extremities, which showed mild atrophy. She exhibited quadriceps sparing, as knee extension strength was 5/5 bilaterally on the Medical Research Council scale, while knee flexion and hip flexion strength were 2/5 bilaterally. Ankle dorsiflexion and eversion were 1/5 on the right side and 0/5 on the left. The distal upper extremities were less severely affected. Electromyography data were unavailable. Progression was slow and after more than 15 years, she remained ambulant with assistance at age 53. Serum CK was mildly elevated at 370 U/L, and there was no evidence of cardiac, respiratory, or non-muscular neurological involvement. A first biopsy taken from the left quadriceps was reported as normal. Subsequent biopsy of biceps tissue revealed pathology that was strikingly focal; affected areas showed vacuoles with thin basophilic rimming, as well as marked variation in fiber size, rounded fibers, infiltration of endomysial tissue, increased internalized nuclei, and abundant atrophic fibers (Figure 2). On clinical histological examination, cytoplasmic bodies were seen, though rarely, and the vacuoles did not stain positive for amyloid by Congo red.


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

Boyden SE, Duncan AR, Estrella EA, Lidov HG, Mahoney LJ, Katz JS, Kunkel LM, Kang PB - BMC Med. Genet. (2011)

Pedigree. Subjects with DNA samples available and tested are labeled with their identification number. Black-filled symbols represent individuals affected with HIBM2, with onset in their 20s or 30s. Tested patients were compound heterozygous with genotype NM_005476.5: c.[1816+5G>A]+[2086G>A]. The gray-filled symbol represents an individual presenting in his 70s with mild HIBM-like symptoms, with genotype NM_005476.5: c.[1816+5G>A]+[=]. Arrow indicates the proband.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3141630&req=5

Figure 1: Pedigree. Subjects with DNA samples available and tested are labeled with their identification number. Black-filled symbols represent individuals affected with HIBM2, with onset in their 20s or 30s. Tested patients were compound heterozygous with genotype NM_005476.5: c.[1816+5G>A]+[2086G>A]. The gray-filled symbol represents an individual presenting in his 70s with mild HIBM-like symptoms, with genotype NM_005476.5: c.[1816+5G>A]+[=]. Arrow indicates the proband.
Mentions: The family consisted of five affected siblings, two unaffected siblings, their unaffected mother, and their father, who had mild distal weakness noted late in life (Figure 1). The female proband presented at age 37 with weakness, fatigue while walking, and difficulty walking and climbing stairs. Her weakness was predominantly in the distal lower extremities, which showed mild atrophy. She exhibited quadriceps sparing, as knee extension strength was 5/5 bilaterally on the Medical Research Council scale, while knee flexion and hip flexion strength were 2/5 bilaterally. Ankle dorsiflexion and eversion were 1/5 on the right side and 0/5 on the left. The distal upper extremities were less severely affected. Electromyography data were unavailable. Progression was slow and after more than 15 years, she remained ambulant with assistance at age 53. Serum CK was mildly elevated at 370 U/L, and there was no evidence of cardiac, respiratory, or non-muscular neurological involvement. A first biopsy taken from the left quadriceps was reported as normal. Subsequent biopsy of biceps tissue revealed pathology that was strikingly focal; affected areas showed vacuoles with thin basophilic rimming, as well as marked variation in fiber size, rounded fibers, infiltration of endomysial tissue, increased internalized nuclei, and abundant atrophic fibers (Figure 2). On clinical histological examination, cytoplasmic bodies were seen, though rarely, and the vacuoles did not stain positive for amyloid by Congo red.

Bottom Line: 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 father of the proband was heterozygous for the splice site mutation and exhibited mild distal weakness late in life.Our 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.

View Article: PubMed Central - HTML - PubMed

Affiliation: Division of Genetics, Children's Hospital Boston, Boston, MA 02115, USA.

ABSTRACT

Background: Many 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.

Methods: We 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.

Results: The 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.

Conclusions: Our 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.

Show MeSH
Related in: MedlinePlus