Dominant GDAP1 founder mutation is a common cause of axonal Charcot-Marie-Tooth disease in Finland

We describe a founder mutation in the gene encoding ganglioside-induced differentiation associated-protein 1 (GDAP1), leading to amino acid change p.H123R, as a common cause of autosomal dominant axonal Charcot-Marie-Tooth (CMT2) neuropathy in Finland. The mutation explains up to 14 % of CMT2 in Finland, where most patients with axonal neuropathy have remained without molecular diagnosis. Only three families out of 28 were found to carry putative disease mutations in the MFN2 gene encoding mitofusin 2. In addition, the MFN2 variant p.V705I was commonly found in our patients, but we provide evidence that this previously described mutation is a common polymorphism and not pathogenic. GDAP1-associated polyneuropathy caused predominantly a mild and slowly progressive phenotype. Besides distal leg muscle weakness, most patients showed mild proximal weakness, often with asymmetry and pes cavus. Our findings broaden the understanding of GDAP1 mutations in CMT2 phenotypes and provide support for the use of whole-exome sequencing in CMT gene diagnostics.     

Mutational mechanisms in MFN2‐related neuropathy: compound heterozygosity for recessive and semidominant mutations

Mitofusin‐2 (MFN2) mutations are the most common cause of autosomal dominant axonal Charcot‐Marie‐Tooth disease (CMT, type 2A), sometimes complicated by additional features such as optic atrophy (CMT6) and upper motor neuron involvement (CMT5). Several pathogenic mutations are reported, mainly acting in a dominant fashion, although few sequence variants behaved as recessive or semidominant in rare homozygous or compound heterozygous patients. We describe a 49‐year‐old woman with CMT5 associated with compound heterozygosity for two MFN2 variants, one already reported missense mutation (c.748C>T, p.R250W) and a novel nonsense sequence change (c.1426C>T, p.R476*). Her mother, carrying the p.R250W variant, had very late‐onset minimal axonal neuropathy, whilst the father harboring the nonsense sequence change had neither clinical nor electrophysiological neuropathy. The missense mutation is likely pathogenic according to in silico analyses and a previous report, while the nonsense variant is predicted to behave as a null allele. The p.R250W variant behaves as semidominant by causing only a mild, almost subclinical, neuropathy when heterozygous; the nonsense mutation in the father was phenotypically silent, suggesting that haploinsufficiency for MFN2 is not disease causative, but was deleterious in the daughter who had only one active mutated MFN2 allele.     

Exome sequencing reveals mutations in MFN2 and GDAP1 in severe Charcot–Marie–Tooth disease

The aim of our study was to characterize electrophysiologically and explain the genetic cause of severe Charcot–Marie–Tooth (CMT) in a 3.5‐year‐old with asymptomatic parents and a maternal grandfather with a history of mild adult‐onset axonal neuropathy. Severity of neuropathy was assessed by Charcot–Marie–Tooth neuropathy score (CMTNS). Whole‐exome sequencing was performed using an Illumina TruSeq Exome Enrichment Kit on the HiSeq 1500 with results followed up by Sanger sequencing on an ABI Prism 3500XL (Applied Biosystems, Foster City, CA, USA). Paternity was confirmed using a panel of 15 hypervariable markers. Electrophysiological studies demonstrated severe axonal sensory‐motor neuropathy in the proband, mild motor neuropathy in his mother, and mild sensory‐motor neuropathy in his grandfather. CMTNS in the proband, his mother, and grandfather was 21, 1, and 12, respectively. On genetic analysis, the boy was found to carry a heterozygous dominant MFN2 T236M mutation transmitted via the maternal line and a de novo GDAP1 H123R mutation. Our findings emphasize the need to search for more than one causative mutation when significant intrafamilial variability of CMT phenotype occurs and underline the role of whole‐exome sequencing in the diagnosis of compound forms of CMT disease.     

Phenotypical features of the p.R120W mutation in the GDAP1 gene causing autosomal dominant Charcot-Marie-Tooth disease

Mutations in the ganglioside-induced-differentiation-associated protein 1 gene (GDAP1) can cause Charcot-Marie-Tooth (CMT) disease with demyelinating (CMT4A) or axonal forms (CMT2K and ARCMT2K). Most of these mutations present a recessive inheritance, but few autosomal dominant GDAP1 mutations have also been reported. We performed a GDAP1 gene screening in a clinically well-characterized series of 81 index cases with axonal CMT neuropathy, identifying 17 patients belonging to 4 unrelated families in whom the heterozygous p.R120W was found to be the only disease-causing mutation. The main objective was to fully characterize the neuropathy caused by this mutation. The clinical picture included a mild-moderate phenotype with onset around adolescence, but great variability. Consistently, ankle dorsiflexion and plantar flexion were impaired to a similar degree. Nerve conduction studies revealed an axonal neuropathy. Muscle magnetic resonance imaging studies demonstrated selective involvement of intrinsic foot muscles in all patients and a uniform pattern of fatty infiltration in the calf, with distal and superficial posterior predominance. Pathological abnormalities included depletion of myelinated fibers, regenerative clusters and features of axonal degeneration with mitochondrial aggregates. Our findings highlight the relevance of dominantly transmitted p.R120W GDAP1 gene mutations which can cause an axonal CMT with a wide clinical profile.     

A novel EGR2 mutation within a family with a mild demyelinating form of Charcot-Marie-Tooth disease

Mutations of the early growth response 2 (EGR2) gene have been reported in a variety of severe demyelinating neuropathies such as autosomal recessive congenital hypomyelinating neuropathy, autosomal dominant child-onset Dejerine-Sottas neuropathy, and autosomal dominant adult-onset Charcot-Marie-Tooth disease (CMT). Here, we report on a heterozygous mutation in EGR2 (c.1160C>A), which results in threonine at position 387 being changed to asparagine, in a family with a mild demyelinating form of adult-onset CMT. Of note, both the proband and her asymptomatic son exhibited neither pes cavus nor champagne-bottle leg atrophy, suggesting that the heterozygous T387N mutation may result in a relatively mild phenotype of demyelinating CMT.     

GDAP1 mutations in Czech families with early-onset CMT

Mutations in the ganglioside-induced differentiation associated protein-1 gene (GDAP1) cause autosomal recessive (AR) demyelinating or axonal Charcot-Marie-Tooth neuropathy (CMT). In order to establish the spectrum and frequency of GDAP1 mutations in Czech population, we sequenced GDAP1 in 74 Czech patients from 69 unrelated families with early-onset demyelinating or axonal CMT compatible with AR inheritance. We identified three isolated patients with GDAP1 mutations in both alleles. In one additional sporadic and one familial case, the second pathogenic mutation remained unknown. Overall, we detected two different mutations, a novel R191X nonsense and a L239F missense mutation. L239F previously described in a German-Italian family is a prevalent mutation in Czech population and we give evidence for its common ancestral origin. All Czech GDAP1 patients developed involvement of all four limbs evident by the end of second decade, except for one isolated patient showing very slow disease progression. All patients displayed axonal type of neuropathy.     

Interaction of heritable and estrogen-induced thrombophilia: possible etiologies for ischemic optic neuropathy and ischemic stroke

Our specific aim was to assess how thrombophilic exogenous estrogens interacted with heritable thrombophilias leading to non-arteritic ischemic optic neuropathy (NAION) and ischemic stroke. Coagulation measures were performed in a 74 year old patient and her immediate family. The proband had a 47 year history of 9 previous thrombotic episodes, and developed unilateral NAION 4 years after starting estrogen replacement therapy (ERT). The proband was heterozygous for two thrombophilic gene mutations (G20210A prothrombin gene, platelet glycoprotein IIIa P1A1/A2 polymorphism), and homozygous for the C677T mutation in the methylenetetrahydrofolate reductase (MTHFR) gene. Of 238 normal controls, none had these 3 gene mutations together. The proband's mother and brother had deep venous thrombosis (DVT). The proband's brother, sister, nephew, daughter, and two granddaughters were homozygous for the C677T MTHFR mutation. The proband's brother was heterozygous for the G20210A prothrombin gene mutation. The proband's niece was heterozygous for the G20210A prothrombin gene mutation, homozygous for the C677T MTHFR mutation, homozygous for the hypofibrinolytic 4G polymorphism of the plasminogen activator inhibitor-1 (PAI-1) gene, and heterozygous for the platelet glycoprotein IIIa P1A1/A2 polymorphism. Of 238 normal controls, none had the niece's combination of 4 gene mutations. When ERT-mediated thrombophilia was superimposed on the proband's heritable thrombophilias, unilateral ischemic optic neuropathy developed, her tenth thrombotic event over a 5 decade period. When estrogen-progestin oral contraceptives were given to the proband's niece, she had an ischemic stroke at age 22. Exogenous estrogen-mediated thrombophilia superimposed on heritable thrombophilia and hypofibrinolysis is associated with arterial and venous thrombi, and appears to be a preventable, and potentially reversible etiology for ischemic optic neuropathy and ischemic stroke.     

A novel autosomal dominant GDAP1 mutation in an Italian CMT2 family

We report the clinical, electrophysiological, and skin biopsy findings of an Italian Charcot-Marie-Tooth disease type 2 (CMT2) family with a novel heterozygous GDAP1 mutation. We observed a marked intra-familial phenotypic variability, in age at onset and disease severity which ranged from a typical CMT phenotype to an asymptomatic status. Electrophysiological study, consistent with an axonal sensory-motor neuropathy, confirmed a different degree of severity and disclosed minimal electrophysiological abnormalities also in the asymptomatic subjects. Skin biopsy findings showed a variable loss of large and small somatic nerve fibers. Molecular analysis identified a novel heterozygous missense mutation (Arg120Gly) in the GDAP1 gene which co-segregated with the disease within the pedigree. In conclusion, our findings confirm that the GDAP1 autosomal dominant mutations underlie a pronounced phenotypic variability, mimicking the effects of reduced penetrance. Notably, electrophysiological study in this family allowed to reveal hidden positive family history and assess a dominant inheritance pattern, revealing subclinical neuropathy in asymptomatic mutation carriers.     

Two families of Charcot-Marie-Tooth disease with Adie's pupil, axonal neuropahy and the Thr124Met mutation in the peripheral myelin protein zero gene]

We reported two families of Charcot-Marie-Tooth disease (CMT) with Thr124Met mutation in the peripheral myelin protein zero (MPZ). The clinical features of the proband patients of both families showed Adie's pupil, severe sensory dominant neuropathy in lower extremities, and axonal changes in sural nerve biopsies and nerve conduction studies. Muscle atrophy and weakness was mild in the lower legs, while sensory impairment was marked. The proband patient of family 1 had four symptomatic siblings and one of them showed Adie's pupil. The elderly daughter of the proband of family 2 showed Adie's pupil and younger daughter showed photophobia. The biopsied sural nerves of both proband patients revealed prominent axonal sprouting, and sub-perineurial edema and mild fascicular enlargement. Segmental demyelination was not frequent in teased fiber assessment. The present two family cases strongly suggest that this MPZ gene mutation (Thr124Met) could be present among the patients with CMT type 2, axonal form. Furthermore, the patients showing sensory neuropathy and Adie's pupil may need to be reexamined with this mutation. It is also necessary to reassess genotype-phenotype correlation in CMT patients particularly in reference to type 1 and type 2.     

Mutations in the mitofusin 2 gene are the most common cause of Charcot-Marie-Tooth type 2 disease

In contrast to Charcot-Marie-Tooth type 1 disease (CMT1), which is most commonly caused by 17p11.2-p12 duplication (in 70% of CMT1 cases), the axonal form of hereditary motor and sensory neuropathy (CMT2) seemed to be a genetically heterogeneous disease group, with no single gene playing a major pathogenetic role. In 2004, 10 mutations were identified in CMT2A families in the MFN2 gene coding for the mitochondrial protein mitofusin-2, previously mapped to the 1p35-36 locus. In the last two years, MFN2 gene mutations were shown to be the most common cause of autosomal dominant hereditary axonopathy. In addition, MFN2 gene mutations were also identified in CMT type 6 (axonal neuropathy with optic nerve atrophy). Recent reports indicate that some MFN2 gene mutations may by inherited as autosomal recessive traits. As MFN2 gene mutations are the most common cause of autosomal dominant CMT2 disease (33% of cases), MFN2 gene testing may be considered a diagnostic test for CMT2.     

Clinical and molecular evidence of possible digenic inheritance for MFN2/GDAP1 genes in Charcot-Marie-Tooth disease

Charcot Marie Tooth disease (CMT) is a progressive motor and sensory polyneuropathy, it is characterized by a very heterogeneous molecular basis and phenotype. MFN2 and GDAP1 participate in mitochondrial energy metabolism and the rare coinheritance of its pathogenic variants has been associated with a cumulative effect in the observed phenotype. We describe a patient with a severe axonal CMT and inherited heterozygous MFN2 (p.Leu741Val) and GDAP1 (p.Gln163*) variants. In accordance with a possible digenic inheritance, none of the heterozygous carriers in his family were symptomatic or exhibited electrophysiological abnormalities. We also review all of the previously reported patients with coinheritance of variants in these two genes; similar to our patient, all exhibit a predominantly axonal severe CMT phenotype. Our findings expand the genotypic spectrum of CMT and further support that digenic inheritance should be considered for analyzing and counseling CMT patients.     

Pseudodominant inheritance pattern in a family with CMT2 caused by GDAP1 mutations

We report a family in which an autosomal dominantly inherited Charcot‐Marie‐Tooth (CMT) disease type 2 was suspected. The affected family members (proband, sister, father, and paternal aunt) showed intrafamilial clinical variability. The proband needed walking aids since adolescence because of generalized muscle weakness. The sister showed the same symptoms although to a lesser extent. The father and paternal aunt had foot deformity and atrophy of lower legs. A homozygous GDAP1 mutation was found in the proband and in the sister. Further testing showed compound heterozygous GDAP1 mutations in the father and paternal aunt. In this CMT2 family with a pseudodominant inheritance pattern DNA‐diagnostics revealed the presence of both homozygous and compound heterozygous GDAP1 mutations. We recommend including multiple family members in genetic studies on CMT families.     

Axonal neuropathy with optic atrophy is caused by mutations in mitofusin 2

OBJECTIVE: Charcot-Marie-Tooth (CMT) neuropathy with visual impairment due to optic atrophy has been designated as hereditary motor and sensory neuropathy type VI (HMSN VI). Reports of affected families have indicated autosomal dominant and recessive forms, but the genetic cause of this disease has remained elusive. METHODS: Here, we describe six HMSN VI families with a subacute onset of optic atrophy and subsequent slow recovery of visual acuity in 60% of the patients. Detailed clinical and genetic studies were performed. RESULTS: In each pedigree, we identified a unique mutation in the gene mitofusin 2 (MFN2). In three families, the MFN2 mutation occurred de novo; in two families the mutation was subsequently transmitted from father to son indicating autosomal dominant inheritance. INTERPRETATION: MFN2 is a mitochondrial membrane protein that was recently reported to cause axonal CMT type 2A. It is intriguing that MFN2 shows functional overlap with optic atrophy 1 (OPA1), the protein underlying the most common form of autosomal dominant optic atrophy, and mitochondrial encoded oxidative phosphorylation components as seen in Leber's hereditary optic atrophy. We conclude that autosomal dominant HMSN VI is caused by mutations in MFN2, emphasizing the important role of mitochondrial function for both optic atrophies and peripheral neuropathies.     

Novel GDAP1 Mutation in a Turkish Family with CMT2K (CMT2K with Novel GDAP1 Mutation)

Mutations in the ganglioside-induced differentiation-associated protein 1 gene (GDAP1) cause Charcot–Marie–Tooth type 2 (CMT2), a severe autosomal recessive form of neuropathy associated with axonal phenotypes. It has been screened in this study for the presence of mutations in the coding region of GDAP1, which maps to chromosome 8q21, in a family with CMT2. To date, 29 mutations in the GDAP1 have been reported in patients of different ethnic origins. Here, we report a novel missense mutation (c.836A>G), and two polymorphisms: a silent variant (c.102G>C), and a 5′-splice site mutation (IVS5+24C>T) in GDPA1 gene identified in a five generation Turkish family with autosomal recessive CMT2.     

A novel GDAP1 mutation P78L responsible for CMT4A disease in three Moroccan families

BACKGROUND: The gene encoding the ganglioside-induced-differentiation-associated protein 1 (GDAP1) has been associated with both axonal and demyelinating neuropathy. Up to date, 25 mutations in the GDAP1 gene have been reported in patients from different origins. METHODS: Three Moroccan families with early onset ARCMT1 and autosomal recessive inheritance were genotyped to test linkage to 8q21.3 and their GDAP1 gene coding exons screened for mutations. RESULTS: A novel C233T transversion at codon 78 (P78L) was detected in 6 patients from 3 unrelated families. The mutation was found to be homozygous in two families and compound heterozygous in association with the already reported S194X mutation in one family. The P78L mutation was associated with a common haplotype suggesting a Moroccan founder mutation. The patients had symptoms within the two first years of life and developed common phenotype of CMT4A with evident hoarse-voice in two cases with the longer disease duration. CONCLUSION: P78L mutation was associated with a common haplotype suggesting a common ancestor.     

Charcot–Marie–Tooth disease type 2J with <Emphasis Type="Italic">MPZ</Emphasis> Thr124Met mutation: clinico-electrophysiological and MRI study of a family

The purpose of the present study was to describe clinico-electrophysiological features and lower limb muscle MRI findings in a CMT2J pedigree due to MPZ Thr124Met mutation. We examined the proband, aged 56 years, and her affected daughter and son, aged 30 and 29 years. Disease severity in terms of ability to walk and run was established using a nine-point functional disability scale (FDS). We administered the CMT neuropathy score (CMTNS) based on patient’s symptoms, neurologic examination and neurophysiologic testing. All three patients had non-symptomatic Adie’s pupil. The proband and her son presented with late-onset lower limb sensorimotor neuropathy and pes cavus; the proband’s daughter had no signs of polyneuropathy. FDS score was 4 in the proband, 2 in her son, and 0 (normal) in her daughter. In both symptomatic patients, electrophysiological study showed a pattern of length-dependent axonal neuropathy mainly involving lower limb nerves; this was normal in the other patient. CMTNS was 18 in the proband, 12 in her son, and 0 (normal) in her daughter. MRI of foot and leg musculature was normal in the proband’s daughter, whereas the other two patients showed massive fatty atrophy of intrinsic foot musculature, extensive and diffuse fatty atrophy of leg muscles in the proband, and mild distally accentuated fatty infiltration of calf muscles in her son. Muscle edema, detected only in the proband’s son, was present in 7 out of 22 (33%) of visualized leg muscles, whereas contrast enhancement occurred in 6 of them. The reported mutation may manifest with either isolated Adie’s pupil or pupil abnormalities with late-onset sensorimotor length-dependent axonal polyneuropathy, though the presence of pes cavus might indicate an earlier onset. MRI examination helps to delineate an accurate extent of muscle involvement in the disease.     

腓骨肌萎缩症2A2A型家系的神经电生理及基因突变分析

目的探讨一个腓骨肌萎缩症(charcot-marie-tooth,CMT)家系的临床表现、神经电生理学和基因突变特点。方法收集家系先证者及其他成员的临床资料,对先证者进行神经电生理学检查和全外显子组基因测序,用Sanger测序技术对先证者及其家系进行突变位点验证。应用计算机软件预测突变位点氨基酸进化保守性和突变可能导致的蛋白质结构和功能变化,分析突变位点的性质。结果先证者儿童期发病,出现双下肢对称性肌肉无力伴跟腱反射消失及足部畸形,其母亲有类似症状。先证者神经电生理检查示运动和感觉神经纤维脱髓鞘及轴索性改变。基因检测发现先证者和母亲MFN2基因第11个外显子均检出c.1066A>G(p.T356A)杂合错义突变;先证者姐姐和父亲未检测到该突变。用PolyPhen-2和MutationTaster软件预测该突变为致病性,突变区域序列在不同物种间高度保守。结论儿童CMT2A2A患者的神经电生理、临床特点、发病机制及相关基因表型均有改变,此可为儿童CMT的临床诊断提供依据。     

Novel mutations in the GDAP1 gene in patients affected with early-onset axonal Charcot-Marie-Tooth type 4A

We report a detailed study of eight patients from four Italian families presenting with autosomal recessive axonal Charcot-Marie-Tooth disease (AR-CMT2), characterized by early-onset and progressive severe weakness of all limbs. Vocal cord paresis was present in two cases. Sural nerve biopsy performed in three patients showed a severe neuropathy characterized by a predominant axonal involvement. Five novel mutations (p.Gln99stop, p.Gln122Lys, p.Arg125stop, p.Val219Asp, p.Asn297Lys) and one previously reported mutation (p.Leu239Phe) were identified in GDAP1 gene. GDAP1 mutations should be considered both in recessive and sporadic cases of early-onset axonal CMT.     

A new missense <Emphasis Type="Italic">GDAP1</Emphasis> mutation disturbing targeting to the mitochondrial membrane causes a severe form of AR-CMT2C disease

Charcot–Marie–Tooth disease (CMT) caused by mutations in the ganglioside-induced differentiation-associated protein 1 (GDAP1) gene is characterized by a spectrum of phenotypes. Recurrent nonsense mutations (Q163X and S194X) showing regional distribution segregate with an early onset, severe course of recessive CMT disease with early loss of ambulancy. Missense mutations in GDAP1 have been reported in sporadic CMT cases with variable course of disease, among them the recurrent L239F missense GDAP1 mutation occurring in the European population. Finally, some GDAP1 mutations are associated with a mild form of CMT inherited as an autosomal dominant trait. In this study, we characterize the CMT phenotype in one Polish family with recessive trait of inheritance at the clinical, electrophysiological, morphological, cellular, and genetic level associated with a new Gly327Asp mutation in the GDAP1 gene. In spite of the nature of Gly327Asp mutation (missense), the CMT phenotype associated with this variant may be characterized as an early onset, severe axonal neuropathy, with severe skeletal deformities. The mutation lies within the transmembrane domain of GDAP1 and interferes with the mitochondrial targeting of the protein, similar to the loss of the domain in the previously reported Q163X and S194X mutations. We conclude that the loss of mitochondrial targeting is associated with a severe course of disease. Our study shows that clinical outcome of CMT disease caused by mutations in the GDAP1 gene cannot be predicted solely on the basis of genetic results (missense/nonsense mutations).