Development of MRC Centre MRI calf muscle fat fraction protocol as a sensitive outcome measure in Hereditary Sensory Neuropathy Type 1

OBJECTIVES

Hereditary sensory neuropathy type 1 (HSN1) is a rare, slowly progressive neuropathy causing profound sensory deficits and often severe motor loss. L-serine supplementation is a possible candidate therapy but the lack of responsive outcome measures is a barrier for undertaking clinical trials in HSN1. We performed a 12-month natural history study to characterise the phenotype of HSN1 and to identify responsive outcome measures.

METHODS

Assessments included Charcot-Marie-Tooth Neuropathy Score version 2 (CMTNSv2), CMTNSv2-Rasch modified, nerve conduction studies, quantitative sensory testing, intraepidermal nerve fibre density (thigh), computerised myometry (lower limbs), plasma 1-deoxysphingolipid levels, calf-level intramuscular fat accumulation by MRI and patient-based questionnaires (Neuropathic Pain Symptom Inventory and 36-Short Form Health Survey version 2 [SF-36v2]).

RESULTS

35 patients with HSN1 were recruited. There was marked heterogeneity in the phenotype mainly due to differences between the sexes: males generally more severely affected. The outcome measures that significantly changed over 1 year and correlated with CMTNSv2, SF-36v2-physical component and disease duration were MRI determined calf intramuscular fat accumulation (mean change in overall calf fat fraction 2.36%, 95% CI 1.16 to 3.55, p=0.0004), pressure pain threshold on the hand (mean change 40 kPa, 95% CI 0.7 to 80, p=0.046) and myometric measurements of ankle plantar flexion (median change -0.5 Nm, IQR -9.5 to 0, p=0.0007), ankle inversion (mean change -0.89 Nm, 95% CI -1.66 to -0.12, p=0.03) and eversion (mean change -1.61 Nm, 95% CI -2.72 to -0.51, p=0.006). Intramuscular calf fat fraction was the most responsive outcome measure.

CONCLUSION

MRI determined calf muscle fat fraction shows validity and high responsiveness over 12 months and will be useful in HSN1 clinical trials.

IGHMBP2 mutation associated with organ-specific autonomic dysfunction

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Novel IGHMBP2 variant found in a patient with early onset severe peripheral neuropathy.

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IGHMBP2 mutations may cause enteral autonomic dysfunction.

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Autonomic dysfunction in IGHMBP2-related disorders may be severe requiring parenteral nutrition.

Biallelic mutations in the IGHMBP2 have been associated with two distinct phenotypes: spinal muscular atrophy with respiratory distress type 1 (SMARD1) and CMT2S. We describe a patient who developed progressive muscle weakness and wasting in her upper and lower limbs from infancy. She developed respiratory involvement at age 9, eventually requiring 24-h non-invasive ventilation, and severe autonomic dysfunction restricted to the gastrointestinal tract. Neurophysiological studies at age 27 years revealed absent sensory and motor responses and severe chronic denervation changes in proximal muscles of the upper limbs. Targeted multigene panel sequencing detected a novel homozygous missense variant in the IGHMBP2 gene (c.1325A > G; p.Tyr442Cys). This variant was validated by Sanger sequencing and co-segregation analysis confirmed that both parents were asymptomatic heterozygous carriers. This case report confirms that IGHMBP2 related disorders can result in a severe peripheral neuropathy with gastrointestinal autonomic dysfunction requiring parenteral nutrition.

A de novo dominant mutation in KIF1A associated with axonal neuropathy, spasticity and autism spectrum disorder

Mutations in the kinesin family member 1A (KIF1A) gene have been associated with a wide range of phenotypes including recessive mutations causing hereditary sensory neuropathy and hereditary spastic paraplegia and de novo dominant mutations causing a more complex neurological disorder affecting both the central and peripheral nervous system. We identified by exome sequencing a de novo dominant missense variant, (c.38G>A, p.R13H), within an ATP binding site of the kinesin motor domain in a patient manifesting a complex phenotype characterized by autism spectrum disorder (ASD), spastic paraplegia and axonal neuropathy. The presence of ASD distinguishes this case from previously reported patients with de novo dominant mutations in KIF1A.

Genetic and clinical characteristics of NEFL-related Charcot-Marie-Tooth disease

OBJECTIVES

To analyse and describe the clinical and genetic spectrum of Charcot-Marie-Tooth disease (CMT) caused by mutations in the neurofilament light polypeptide gene (NEFL).

METHODS

Combined analysis of newly identified patients with NEFL-related CMT and all previously reported cases from the literature.

RESULTS

Five new unrelated patients with CMT carrying the NEFL mutations P8R and N98S and the novel variant L311P were identified. Combined data from these cases and 62 kindreds from the literature revealed four common mutations (P8R, P22S, N98S and E396K) and three mutational hotspots accounting for 37 (55%) and 50 (75%) kindreds, respectively. Eight patients had de novo mutations. Loss of large-myelinated fibres was a uniform feature in a total of 21 sural nerve biopsies and 'onion bulb' formations and/or thin myelin sheaths were observed in 14 (67%) of them. The neurophysiological phenotype was broad but most patients with E90K and N98S had upper limb motor conduction velocities <38 m/s. Age of onset was ≤3 years in 25 cases. Pyramidal tract signs were described in 13 patients and 7 patients were initially diagnosed with or tested for inherited ataxia. Patients with E90K and N98S frequently presented before age 3 years and developed hearing loss or other neurological features including ataxia and/or cerebellar atrophy on brain MRI.

CONCLUSIONS

NEFL-related CMT is clinically and genetically heterogeneous. Based on this study, however, we propose mutational hotspots and relevant clinical-genetic associations that may be helpful in the evaluation of NEFL sequence variants and the differential diagnosis with other forms of CMT.

Mutations in noncoding regions of GJB1 are a major cause of X-linked CMT

OBJECTIVE

To determine the prevalence and clinical and genetic characteristics of patients with X-linked Charcot-Marie-Tooth disease (CMT) due to mutations in noncoding regions of the gap junction β-1 gene (GJB1).

METHODS

Mutations were identified by bidirectional Sanger sequence analysis of the 595 bases of the upstream promoter region, and 25 bases of the 3' untranslated region (UTR) sequence in patients in whom mutations in the coding region had been excluded. Clinical and neurophysiologic data were retrospectively collected.

RESULTS

Five mutations were detected in 25 individuals from 10 kindreds representing 11.4% of all cases of CMTX1 diagnosed in our neurogenetics laboratory between 1996 and 2016. Four pathogenic mutations, c.-17G>A, c.-17+1G>T, c.-103C>T, and c.-146-90_146-89insT were detected in the 5'UTR. A novel mutation, c.*15C>T, was detected in the 3' UTR of GJB1 in 2 unrelated families with CMTX1 and is the first pathogenic mutation in the 3'UTR of any myelin-associated CMT gene. Mutations segregated with the phenotype, were at sites predicted to be pathogenic, and were not present in the normal population.

CONCLUSIONS

Mutations in noncoding DNA are a major cause of CMTX1 and highlight the importance of mutations in noncoding DNA in human disease. Next-generation sequencing platforms for use in inherited neuropathy should therefore include coverage of these regions.

SIGMAR1 mutation associated with autosomal recessive Silver-like syndrome

OBJECTIVE

To describe the genetic and clinical features of a simplex patient with distal hereditary motor neuropathy (dHMN) and lower limb spasticity (Silver-like syndrome) due to a mutation in the sigma nonopioid intracellular receptor-1 gene (SIGMAR1) and review the phenotypic spectrum of mutations in this gene.

METHODS

We used whole-exome sequencing to investigate the proband. The variants of interest were investigated for segregation in the family using Sanger sequencing. Subsequently, a larger cohort of 16 unrelated dHMN patients was specifically screened for SIGMAR1 mutations.

RESULTS

In the proband, we identified a homozygous missense variant (c.194T>A, p.Leu65Gln) in exon 2 of SIGMAR1 as the probable causative mutation. Pathogenicity is supported by evolutionary conservation, in silico analyses, and the strong phenotypic similarities with previously reported cases carrying coding sequence mutations in SIGMAR1. No other mutations were identified in 16 additional patients with dHMN.

CONCLUSIONS

We suggest that coding sequence mutations in SIGMAR1 present clinically with a combination of dHMN and pyramidal tract signs, with or without spasticity, in the lower limbs. Preferential involvement of extensor muscles of the upper limbs may be a distinctive feature of the disease. These observations should be confirmed in future studies.

Peripheral neuropathy predicts nuclear gene defect in patients with mitochondrial ophthalmoplegia

Mitochondrial ophthalmoplegia is a genetically heterogeneous disorder. Horga et al. investigate whether peripheral neuropathy can predict the underlying genetic defect in patients with progressive external ophthalmoplegia. Results indicate that neuropathy is highly predictive of a nuclear DNA defect and that it is rarely associated with single mitochondrial DNA deletions.

Progressive external ophthalmoplegia is a common clinical feature in mitochondrial disease caused by nuclear DNA defects and single, large-scale mitochondrial DNA deletions and is less frequently associated with point mutations of mitochondrial DNA. Peripheral neuropathy is also a frequent manifestation of mitochondrial disease, although its prevalence and characteristics varies considerably among the different syndromes and genetic aetiologies. Based on clinical observations, we systematically investigated whether the presence of peripheral neuropathy could predict the underlying genetic defect in patients with progressive external ophthalmoplegia. We analysed detailed demographic, clinical and neurophysiological data from 116 patients with genetically-defined mitochondrial disease and progressive external ophthalmoplegia. Seventy-eight patients (67%) had a single mitochondrial DNA deletion, 12 (10%) had a point mutation of mitochondrial DNA and 26 (22%) had mutations in either POLG, C10orf2 or RRM2B, or had multiple mitochondrial DNA deletions in muscle without an identified nuclear gene defect. Seventy-seven patients had neurophysiological studies; of these, 16 patients (21%) had a large-fibre peripheral neuropathy. The prevalence of peripheral neuropathy was significantly lower in patients with a single mitochondrial DNA deletion (2%) as compared to those with a point mutation of mitochondrial DNA or with a nuclear DNA defect (44% and 52%, respectively; P < 0.001). Univariate analyses revealed significant differences in the distribution of other clinical features between genotypes, including age at disease onset, gender, family history, progressive external ophthalmoplegia at clinical presentation, hearing loss, pigmentary retinopathy and extrapyramidal features. However, binomial logistic regression analysis identified peripheral neuropathy as the only independent predictor associated with a nuclear DNA defect (P = 0.002; odds ratio 8.43, 95% confidence interval 2.24–31.76). Multinomial logistic regression analysis identified peripheral neuropathy, family history and hearing loss as significant predictors of the genotype, and the same three variables showed the highest performance in genotype classification in a decision tree analysis. Of these variables, peripheral neuropathy had the highest specificity (91%), negative predictive value (83%) and positive likelihood ratio (5.87) for the diagnosis of a nuclear DNA defect. These results indicate that peripheral neuropathy is a rare finding in patients with single mitochondrial DNA deletions but that it is highly predictive of an underlying nuclear DNA defect. This observation may facilitate the development of diagnostic algorithms. We suggest that nuclear gene testing may enable a more rapid diagnosis and avoid muscle biopsy in patients with progressive external ophthalmoplegia and peripheral neuropathy.

Charcot-Marie-Tooth disease: frequency of genetic subtypes and guidelines for genetic testing

BACKGROUND

Charcot-Marie-Tooth disease (CMT) is a clinically and genetically heterogeneous group of diseases with approximately 45 different causative genes described. The aims of this study were to determine the frequency of different genes in a large cohort of patients with CMT and devise guidelines for genetic testing in practice.

METHODS

The genes known to cause CMT were sequenced in 1607 patients with CMT (425 patients attending an inherited neuropathy clinic and 1182 patients whose DNA was sent to the authors for genetic testing) to determine the proportion of different subtypes in a UK population.

RESULTS

A molecular diagnosis was achieved in 62.6% of patients with CMT attending the inherited neuropathy clinic; in 80.4% of patients with CMT1 (demyelinating CMT) and in 25.2% of those with CMT2 (axonal CMT). Mutations or rearrangements in PMP22, GJB1, MPZ and MFN2 accounted for over 90% of the molecular diagnoses while mutations in all other genes tested were rare.

CONCLUSION

Four commonly available genes account for over 90% of all CMT molecular diagnoses; a diagnostic algorithm is proposed based on these results for use in clinical practice. Any patient with CMT without a mutation in these four genes or with an unusual phenotype should be considered for referral for an expert opinion to maximise the chance of reaching a molecular diagnosis.

Clinical, biochemical and molecular genetic correlations in Friedreich's ataxia

Friedreich's ataxia (FRDA) is an autosomal recessive disorder with a frequency of 1 in 50 000 live births. In 97% of patients it is caused by the abnormal expansion of a GAA repeat in intron 1 of the FRDA gene on chromosome 9, which encodes a 210 amino acid protein called frataxin. Frataxin is widely expressed and has been localized to mitochondria although its function is unknown. We have investigated mitochondrial function, mitochondrial DNA levels, aconitase activity and iron content in tissues from FRDA patients. There were significant reductions in the activities of complex I, complex II/III and aconitase in FRDA heart. Respiratory chain and aconitase activities were decreased although not significantly in skeletal muscle, but were normal in FRDA cerebellum and dorsal root ganglia, although there was a mild decrease in aconitase activity in the latter. Mitochondrial DNA levels were reduced in FRDA heart and skeletal muscle, although in skeletal muscle this was paralleled by a decline in citrate synthase activity. Increased iron deposition was seen in FRDA heart, liver and spleen in a pattern consistent with a mitochondrial location. The iron accumulation, mitochondrial respiratory chain and aconitase dysfunction and mitochondrial DNA depletion in FRDA heart samples largely paralleled those in the yeast YFH1 knockout model, suggesting that frataxin may be involved in mitochondrial iron regulation or iron sulphur centre synthesis. However, the severe deficiency in aconitase activity also suggests that oxidant stress may induce a self-amplifying cycle of oxidative damage and mitochondrial dysfunction, which may contribute to cellular toxicity.

Mitochondrial DNA depletion syndrome is expressed in amniotic fluid cell cultures

Mitochondrial DNA depletion syndrome is an autosomal inherited disease associated with grossly reduced cellular levels of mitochondrial DNA in infancy. Most patients are born after a full and uncomplicated pregnancy, are normal at birth, but develop symptoms in the early neonatal period. These observations have led to the suggestion that the patients have a defect affecting the control of mitochondrial DNA copy number after birth. Using immunocytochemical techniques, we demonstrated that the disease is already expressed in amniotic fluid cells. Detection of mitochondrial DNA depletion in these fetal cells indicates that the defect may already be expressed early in embryological development.

The pharmacokinetics of intravenous ondansetron in patients with hepatic impairment

The pharmacokinetics of the 5-HT3 receptor antagonist ondansetron were investigated following a single 8 mg intravenous dose given over 5 min in 19 patients with varying degrees of hepatic impairment and in six young healthy subjects. In comparison with the healthy controls, the patients with severe hepatic impairment had a lower mean plasma clearance (96 ml min-1 vs 478 ml min-1) and increased AUC (1383 ng ml-1 h vs 279 ng ml-1 h) and t1/2 (21 h vs 3.6 h). These differences were all statistically significant (P < 0.001). The corresponding values for patients with mild or moderate hepatic impairment fell between these extremes. Vss was greater in all patient groups than the control group, but the magnitude of the change was smaller than for the other parameters and did not reflect the increasing severity of hepatic impairment. There were no significant changes in Cmax. There were no drug-related adverse events in the patients studied. It is recommended that the dosing frequency of ondansetron be limited to once daily in patients with severe hepatic impairment.

Bleeding time in patients with hepatic cirrhosis

OBJECTIVE

To determine the frequency of an abnormal bleeding time in patients with cirrhosis and to relate this to known factors that affect primary haemostasis and to the severity of liver disease.

DESIGN

Prospective clinical and laboratory study in patients admitted for complications or investigations of liver disease.

SETTING

Royal Free Hospital hepatobiliary and liver transplantation unit.

SUBJECTS

100 Consecutive inpatients aged 17-74 with various forms of cirrhosis, including alcoholic, biliary, autoimmune, viral, and cryptogenic. At least 10 days had elapsed since any episodes of bleeding, resolution of sepsis, or alcohol intake. No patient was taking any drug known to affect primary haemostasis.

MAIN OUTCOME MEASURES

Bleeding time as measured with the Simplate double blade template device. A bleeding time longer than 10 minutes was considered abnormal. Other measures were platelet count, prothrombin time, partial thromboplastin time, packed cell volume, and blood urea, serum bilirubin, and serum albumin concentrations, all measured on each subject at the same time by standard laboratory methods.

RESULTS

A weak but significant correlation existed between the bleeding time and the platelet count (rs = 0.483; p less than 0.001). There were significantly lower platelet counts, longer prothrombin times, and higher blood urea and serum bilirubin concentrations in the 42 patients with bleeding times of 10 minutes or more compared with the 58 patients with bleeding times less than 10 minutes. Multiple linear regression analysis showed that the bilirubin concentration as well as the platelet count was independently correlated with the bleeding time. The combination of a platelet count greater than 80 x 10(9)/l and a prothrombin time less than 17 seconds (usually taken as safe limits for performing routine liver biopsy) did not predict a normal bleeding time. Ten of 39 patients fulfilling these criteria had a prolonged bleeding time.

CONCLUSIONS

Prolonged bleeding time is common in patients with cirrhosis, even in those with prothrombin times and platelet counts within "safe limits" for invasive procedures. The severity of liver disease as assessed by the bilirubin concentration plays an important part in determining the bleeding time in cirrhosis. The bleeding time should be measured when assessing patients for invasive procedures who have a raised bilirubin concentration or poor hepatic function, even if the platelet count and prothrombin time are considered adequate.

Severe hepatitis caused by cyproterone acetate

A case of severe acute hepatitis caused by cyproterone acetate in a 71 year old man with prostatic carcinoma is reported with a review of the literature on hepatic reactions to this drug. The association between the use of cyproterone acetate and liver abnormalities is poorly documented. This is the fourth published report of adverse hepatic reaction to cyproterone acetate and it substantiates other evidence that cyproterone acetate is potentially hepatotoxic. Monitoring of liver function tests should be mandatory in patients receiving high doses of cyproterone acetate; the drug should be withdrawn immediately if abnormal liver function tests are found.

Metabolism of exogenous S-adenosyl-L-methionine in patients with liver disease

S-Adenosyl-L-methionine (SAMe) is an important methyl group donor for many biochemical reactions. It is widespread in body tissues, including the liver, and is metabolised via 3 main metabolic pathways: transmethyltion, trans-sulphuration and amino-propylation. In chronic liver disease these pathways are impaired, the major abnormality being a reduction in SAMe-synthetase activity. Exogenous SAMe may overcome the effects of impaired SAMe-synthetase activity. Exogenous SAMe is stable in digestive juices and, although well absorbed orally, bioavailability is reduced because of a significant first pass effect in the liver. Dose-dependent peak plasma levels are achieved within 3 to 6 hours of oral administration and plasma levels approach baseline after 24 hours. Volumes of distribution are small. The metabolism of exogenous SAMe appears to follow the known pathways of endogenous SAMe metabolism and the initial data suggest that the process is largely unaffected in patients with chronic liver disease.

2-Methyl-3,3-diphenyl-3-propanolamine (2-MDP) selectively antagonises N-methyl-aspartate (NMA)

Using electrophoretic application to rat central neurones in vivo, and bath application to frog spinal cord in vitro, 2-methyl-3,3-diphenyl-3-propanolamine was found to be a selective antagonist of N-methyl-DL-aspartate, but not of quisqualate or kainate. In this respect the (-) isomer proved to be about three times more potent than the (+) in both preparations.