Marzieh Khani1, Hanieh Taheri1, Hosein Shamshiri2, Hamidreza Moazzeni1, John Hardy3, Jose Tomas Bras3, Kolsoum InanlooRahatloo1, Afagh Alavi4, Shahriar Nafissi5, Elahe Elahi6. 1. School of Biology, College of Science, University of Tehran, Tehran, Iran. 2. Department of Neurology, Tehran University of Medical Sciences, Tehran, Iran. 3. Department of Molecular Neuroscience, Institute of Neurology, University College London, London, UK. 4. Genetics Research Center, University of Social Welfare and Rehabilitation Sciences, Tehran, Iran. 5. Department of Neurology, Tehran University of Medical Sciences, Tehran, Iran. s_nafissi@yahoo.com. 6. School of Biology, College of Science, University of Tehran, Tehran, Iran. elaheelahi@ut.ac.ir.
Abstract
BACKGROUND: Charcot-Marie-Tooth (CMT) disease is a prevalent and heterogeneous peripheral neuropathy. Most patients affected with the axonal form of CMT (CMT2) do not harbor mutations in the approximately 90 known CMT-associated genes. We aimed to identify causative genes in two CMT2 pedigrees. METHODS: Neurologic examination, laboratory tests and brain MRIs were performed. Genetic analysis included exome sequencing of four patients from the two pedigrees. The predicted effect of a deep intronic mutation on splicing was tested by regular and real-time PCR and sequencing. RESULTS: Clinical data were consistent with CMT2 diagnosis. Inheritance patterns were autosomal recessive. Exome data of CMT2-101 did not include mutations in known CMT-associated genes. Sequence data, segregation analysis, bioinformatics analysis, evolutionary conservation, and information in the literature strongly implicated HADHA as the causative gene. An intronic variation positioned 23 nucleotides away from following intron/exon border in GDAP1 was ultimately identified as cause of CMT in CMT2-102. It was shown to affect splicing. CONCLUSION: The finding of a HADHA mutation as a cause of CMT is of interest because its encoded protein is a subunit of the mitochondrial trifunctional protein (MTP) complex, a mitochondrial enzyme involved in long chain fatty acid oxidation. Long chain fatty acid oxidation is an important source of energy for skeletal muscles. The mutation found in CMT2-102 is only the second intronic mutation reported in GDAP1. The mutation in the CMT2-102 pedigree was outside the canonical splice site sequences, emphasizing the importance of careful examination of available intronic sequences in exome sequence data.
BACKGROUND: Charcot-Marie-Tooth (CMT) disease is a prevalent and heterogeneous peripheral neuropathy. Most patients affected with the axonal form of CMT (CMT2) do not harbor mutations in the approximately 90 known CMT-associated genes. We aimed to identify causative genes in two CMT2 pedigrees. METHODS: Neurologic examination, laboratory tests and brain MRIs were performed. Genetic analysis included exome sequencing of four patients from the two pedigrees. The predicted effect of a deep intronic mutation on splicing was tested by regular and real-time PCR and sequencing. RESULTS: Clinical data were consistent with CMT2 diagnosis. Inheritance patterns were autosomal recessive. Exome data of CMT2-101 did not include mutations in known CMT-associated genes. Sequence data, segregation analysis, bioinformatics analysis, evolutionary conservation, and information in the literature strongly implicated HADHA as the causative gene. An intronic variation positioned 23 nucleotides away from following intron/exon border in GDAP1 was ultimately identified as cause of CMT in CMT2-102. It was shown to affect splicing. CONCLUSION: The finding of a HADHA mutation as a cause of CMT is of interest because its encoded protein is a subunit of the mitochondrial trifunctional protein (MTP) complex, a mitochondrial enzyme involved in long chain fatty acid oxidation. Long chain fatty acid oxidation is an important source of energy for skeletal muscles. The mutation found in CMT2-102 is only the second intronic mutation reported in GDAP1. The mutation in the CMT2-102 pedigree was outside the canonical splice site sequences, emphasizing the importance of careful examination of available intronic sequences in exome sequence data.