A novel TFG c.793C>G mutation in a Chinese pedigree with Charcot-Marie-Tooth disease 2

TFG mutation induces haploinsufficiency and drives axonal Charcot-Marie-Tooth disease by causing neurite degeneration

AIMS

TFG-related axonal Charcot-Marie-Tooth (CMT) disease is a late-onset, autosomal dominant, hereditary motor, and sensory neuropathy characterized by slowly progressive weakness and atrophy of the distal muscles. The objective of this study was to determine the common pathogenic mechanism of TFG-related CMT type 2 (CMT2) caused by different mutations and establish a direct association between TFG haploinsufficiency and neurodegeneration.

METHODS

Three individuals carrying the TFG p.G269V mutation but with varying disease durations were studied. The effect of the p.G269V mutation was confirmed by analyzing protein samples extracted from the blood of two individuals. The functional consequences of both CMT2 mutant gene products were evaluated in vitro. The effect of TFG deficiency in the nervous system was examined using zebrafish models and cultured mouse neurons.

RESULTS

Overexpression of p.G269V TFG failed to enhance soluble TFG levels by generating insoluble TFG aggregates. TFG deficiency disrupted neurite outgrowth and induced neuronal apoptosis both in vivo and in vitro and further impaired locomotor capacity in zebrafish, which was consistent with the phenotype in patients. Wnt signaling was activated as a protective factor in response to TFG deficiency.

CONCLUSION

CMT2-related TFG mutation induces TFG haploinsufficiency within cells and drives disease by causing progressive neurite degeneration.

Case Report: Early-Onset Charcot-Marie-Tooth 2N With Reversible White Matter Lesions Repeatedly Mimicked Stroke or Encephalitis

INTRODUCTION

Charcot-Marie-Tooth (CMT) disease is a rare group of peripheral neuropathies with high clinical and genetic heterogeneity. CMT type 2N (CMT 2N) is a rare subtype of CMT with few clinical reports. The clinical presentation mimics that of other diseases, frequently leading to misdiagnoses. We present a case of CMT 2N with reversible white matter lesions (WMLs), which repeatedly mimicked stroke or encephalitis. We include a literature review to the improve management of this disease.

CASE DESCRIPTION

An 8-year-old boy was admitted to the hospital with slurred speech and limb weakness that had persisted for 1 day. Physical examination revealed lethargy, dysarthria, and a positive bilateral Babinski sign. Cerebrospinal fluid (CSF) analysis showed no abnormalities. Brain magnetic resonance imaging (MRI) revealed symmetrical abnormal signal areas in the paraventricular white matter and corpus callosum. The patient was suspected of having viral encephalitis and recovered rapidly after treatment.He was hospitalized 3 years later for limb weakness, barylalia, and facial paralysis persisting for 1 day. MRI showed an abnormal signal in the bilateral corona radiata. He was suspected of having a stroke or encephalitis. He was completely recovered after treatment.After a second 3-year span, he was admitted for another stroke-like episode. Physical examination revealed facial-lingual hemiparesis, mild atrophy of the left thenar muscle, decreased muscle strength in the extremities, and disappearance of the tendon reflex. MRI revealed more pronounced abnormal signals in the bilateral centrum semiovale and corpus callosum. Antibodies against autoimmune encephalitis were negative. A nerve conduction velocity (NCV) study showed motor and sensory four-limb nerve demyelination with axonal damage, most notably at the distal end. His symptoms were resolved after active treatment. A follow-up MRI showed the complete disappearance of the abnormal white matter signal. Whole exon sequencing showed a heterozygous mutation [c.2093C > T(p.Ser698Phe)] in the alanyl-tRNA synthetase 1 gene (AARS1). His mutation, clinical features, and electrophysiological testing led to a diagnosis of CMT 2N.

DISCUSSION

Early-Onset CMT 2N with reversible WMLs can often mimic stroke or encephalopathy. Affected individuals may show an atypical posterior reversible encephalopathy syndrome (PRES) on MRI. Careful family history assessment, physical examination, nerve conduction studies, MRIs, and genetic testing are essential for early diagnosis. Further studies are required to confirm these findings.

A novel TFG c.793C>G mutation in a Chinese pedigree with Charcot-Marie-Tooth disease 2

INTRODUCTION

Mutations within TFG gene were recently reported to cause Charcot-Marie-Tooth disease 2 (CMT2). However, only few pedigrees were documented so far. Here, we reported a Chinese CMT2 pedigree with 8 affected cases and a novel TFG mutation.

METHODS

Clinical evaluation and electrophysiological study were performed in all the affected individuals. Whole-exome sequencing was conducted, followed by the Sanger sequencing and co-segregation analysis to verify the variants.

RESULTS

All cases presented with a phenotype of CMT2, including slowly progressive symmetrical muscle atrophy and weakness predominantly in the distal limbs. Sensory loss in the distal limbs was present in the proband and his father. Age at onset ranged from 37 to 44 years, and was younger in male cases, compared with female cases. Nerve conduction study revealed normal motor nerve conduction velocity but decreased compound muscle action potential. Electromyography test revealed fibrillation potential and positive sharp waves. The creatine kinase activity was increased in all cases. After genetic investigations, we identified a novel TFG c.793C>G (p.Pro265Ala) mutation in the family. This mutation alters the conserved amino acid residue and is absent in 1000G, ExAC, dbSNP, EP6500, and 200 in-house controls. It co-segregated with the disease in the family.

CONCLUSIONS

Our report provided additional evidence that the heterozygous TFG mutations were associated with CMT2.