A Search for Undiagnosed Charcot-Marie-Tooth Disease Among Patients Registered with Unspecified Polyneuropathy in the Danish National Patient Registry

Purpose

In a recent study based on data from the Danish National Patients Registry (DNPR), we reported the prevalence of Charcot-Marie-Tooth disease (CMT) in Denmark to be 22.5 per 100.000. This prevalence is most likely a minimum estimate, as many cases of CMT may be misdiagnosed or remain undiagnosed due to the heterogeneous nature of the disorder. The aim of this study was to investigate the possible number of undiagnosed CMT cases among patients registered with unspecified polyneuropathy (UP) diagnoses in the DNPR.

Patients and Methods

From the DNPR we extracted data on all patients given an UP diagnosis in the period 1977 to 2012. We selected all patients diagnosed with a primary UP diagnosis before age 40 at a department of neurology, neurophysiology, clinical genetics or pediatrics, and excluded all patients with a specified polyneuropathy diagnosis or with diagnostic codes related to alcohol and diabetes mellitus. To assess the proportion of possible CMT patients, we performed medical record review in a random sample of patients diagnosed in the Central Denmark Region. To further investigate the possible overlap between UP and CMT in the DNPR, we performed a series of searches for ICD-8 and ICD-10 codes related to CMT.

Results

Between 1977 and 2012, 30.903 patients were diagnosed with UP without also being diagnosed with CMT. A total of 940 patients fulfilled the selection criteria. We found that 21.5% (95% CI 13.1%–32.2%) of the cases in the random sample fulfilled our criteria for CMT. This estimate increases the prevalence of CMT in Denmark with 3.6 per 100,000 (95% CI 2.4%–5.5%).

Conclusion

This study illustrates how hitherto undiagnosed CMT patients may be identified in the DNPR and further reports the number of possible CMT cases. Our results support the hypothesis that the true prevalence of CMT is higher than recently reported.

Charcot-Marie-Tooth disease in Denmark: a nationwide register-based study of mortality, prevalence and incidence

OBJECTIVES

Charcot-Marie-Tooth disease (CMT) is the most common inherited disorder of the peripheral nervous system, yet no studies have compared the mortality in patients with CMT with that of the general population, and prevalence estimates vary considerably. We performed a nationwide register-based study to investigate the prevalence, incidence and mortality of CMT in Denmark.

DESIGN

We used the Danish National Patient Registry to select all records with primary diagnostic codes for CMT between 1977 and 2012 given at a neurological, neurophysiological, paediatric or clinical genetic clinic. The prevalence was estimated by 31 December 2012, and the incidence rate was calculated based on data from 1988 to 2012. We calculated a standardised mortality ratio (SMR) and an absolute excess mortality rate (AER) stratified according to age categories and disease duration.

RESULTS

A total of 1534 patients (652 women) were identified. The prevalence proportion was 22.5 per 100 000 (95% CI 21.2 to 23.7) and the incidence rate was 0.98 (95% CI 0.93 to 1.04) per 100 000 person-years. The SMR was 1.36 (95% CI 1.21 to 1.53), and the AER was 4.87 per 1000 person-years (95% CI 2.77 to 6.96). We found a significantly higher SMR in cases below 50 years of age, and in cases with disease duration of more than 10 years.

CONCLUSIONS

We found a reduced life expectancy among patients diagnosed with CMT. To our knowledge, this is the first study of CMT to use nationwide register-based data, and the first to report an SMR and an AER.

Magnetic resonance neurography and diffusion tensor imaging of the peripheral nerves in patients with Charcot-Marie-Tooth Type 1A

INTRODUCTION

Investigation of peripheral neuropathies by magnetic resonance neurography (MRN) may provide increased diagnostic accuracy when performed in combination with diffusion tensor imaging (DTI). This study seeks to evaluate DTI in the detection of neuropathic abnormalities in Charcot-Marie-Tooth type 1A (CMT1A).

METHODS

MRI of the sciatic and tibial nerves, including MRN and DTI, was prospectively performed in 15 CMT1A patients and 30 healthy controls (HCs). The following MRI parameters were evaluated and correlated with clinical and neurophysiological findings: T2-relaxation time, proton spin density (PD) and DTI (fractional anisotropy [FA] and apparent diffusion coefficient [ADC]).

RESULTS

DTI showed lower FA and higher ADC in CMT1A compared with HCs. T2 relaxation time showed no difference; however, PD of the sciatic nerve was higher in CMT1A. There were some close associations between neuropathy severity and MRN-DTI, with the closest correlation between FA and nerve conduction velocity in the sciatic nerve (r = 0.76, P < 0.01).

DISCUSSION

MRN-DTI evaluation of sciatic and tibial nerves improves the detection of nerve abnormalities in patients with CMT1A. Muscle Nerve 56: E78-E84, 2017.

Validation of diagnostic codes for Charcot-Marie-Tooth disease in the Danish National Patient Registry

Purpose

To validate the diagnostic codes for Charcot–Marie–Tooth disease (CMT) in the Danish National Patient Registry (DNPR) using positive predictive value (PPV) as a measure of validity.

Patients and methods

We used the DNPR to identify all patients diagnosed with at least one primary CMT diagnosis at a specialized department in the Central Denmark Region during the period 1977–2012. From this population, we randomly selected 123 patients for the validation study. Medical files were reviewed and used as reference standard. We estimated the PPV of the CMT diagnoses and stratified the analysis according to age at diagnosis, gender, and calendar time.

Results

In the DNPR, 275 patients were identified. We were able to retrieve 96 medical files from the random sample of 123 patients, and 85 CMT diagnoses were confirmed. The average age at diagnosis was 42.5 years, and 34% were female. The PPV was 88.5% (95% confidence interval: 80.4–94.1).

Conclusion

The CMT diagnoses in the DNPR have high validity. The DNPR can be used as a data source for epidemiologic research on CMT.

Rothmund-Thomson Syndrome: novel pathogenic mutations and frequencies of variants in the RECQL4 and USB1 (C16orf57) gene

Background

Poikiloderma is defined as a chronic skin condition presenting with a combination of punctate atrophy, areas of depigmentation, hyperpigmentation and telangiectasia. In a variety of hereditary syndromes such as Rothmund–Thomson syndrome (RTS), Clericuzio‐type poikiloderma with neutropenia (PN) and Dyskeratosis Congenita (DC), poikiloderma occurs as one of the main symptoms. Here, we report on genotype and phenotype data of a cohort of 44 index patients with RTS or related genodermatoses.

Methods

DNA samples from 43 patients were screened for variants in the 21 exons of the RECQL4 gene using PCR, SSCP‐PAGE analysis and/or Sanger sequencing. Patients with only one or no detectable mutation in the RECQL4 gene were additionally tested for variants in the 8 exons of the USB1 (C16orf57) gene by Sanger sequencing. The effect of novel variants was evaluated by phylogenic studies, single‐nucleotide polymorphism (SNP) databases and in silico analyses.

Results

We identified 23 different RECQL4 mutations including 10 novel and one homozygous novel USB1 (C16orf57) mutation in a patient with PN. Moreover, we describe 31 RECQL4 and 8 USB1 sequence variants, four of them being novel intronic RECQL4 sequence changes that may have some deleterious effects on splicing mechanisms and need further evaluation by transcript analyses.

Conclusion

The current study contributes to the improvement of genetic diagnostic strategies and interpretation in RTS and PN that is relevant in order to assess the patients' cancer risk, to avoid continuous and inconclusive clinical evaluations and to clarify the recurrence risk in the families. Additionally, it shows that the phenotype of more than 50% of the patients with suspected Rothmund–Thomson disease may be due to mutations in other genes raising the need for further extended genetic analyses.