Stapedial reflex in myotonic dystrophy type 1 and CTG repeat expansion

The severity of clinical symptoms of myotonic dystrophy type 1 (DM1) has been shown to be closely related to the size of a CTG triplet repeat in the gene encoding myotonin protein kinase. Neuro-otological examinations that include eye movement and stapedial reflex (SR) tests can contribute to the quantitative evaluation of muscular involvement in DM1. We previously found that saccadic eye movement velocity in DM1 patients was significantly lower than that in control subjects and that the saccadic velocity and size of the CTG triplet repeat in DM1 patients had a strong inverse correlation. We now report a case-control study that compared the SR wave form (latency: L, contraction time: C₅₀, and relaxation time: D₅₀) measured by the acoustic impedance method in 13 patients with DM1 and in 14 control subjects matched for age and sex. The correlation between the SR wave form and CTG repeat length in DM1 patients obtained by Southern blot analysis with EcoRI was also examined. We found (1) no significant difference between the pure tone audiometric threshold at 500 Hz in the DM1 patients and that in the control subjects; (2) or between the SR thresholds in the patients and controls (500 Hz stimuli); (3) C₅₀ and D₅₀ in DM1 patients to be significantly prolonged, whereas L was not; (4) C₅₀ and D₅₀ in DM1 patients to be significantly correlated with CTG repeat length, whereas L was not. Measurement of SR by the acoustic impedance method is completely non-invasive, causes no discomfort to the subject, and does not depend on the person's effort or cooperation. Our findings show that SR measurement can be used for a quantitative evaluation of muscle involvement in DM1. We believe that the prolongation of D₅₀ in DM1 is caused by myotonia, which has to be confirmed by further clinical and pathological studies. Received: 9 February 2001, Received in revised form: 11 April 2001, Accepted: 23 April 2001     

Saccadic slowing in myotonic dystrophy and CTG repeat expansion

Recent studies have shown that the severity of the several clinical symptoms of myotonic dystrophy (DM) is closely related to the size of a CTG triplet repeat in the gene encoding myotonin protein kinase. Although neurotological findings, including saccadic slowing in patients with DM, have been reported, the relationship between these neurotological findings and elongation of the CTG triplet repeat has not been discussed to our knowledge. We made a case-control study that compared the saccadic velocity in 13 patients with DM and in 13 controls matched for age and sex. We also examined the correlation between the saccadic velocity in DM patients and the size of the expanded DNA fragment (EF) obtained by Southern blot analysis with EcoRI or BglI. We found: (1) The primary eye position was normal in 9 of 12 patients. Divergent strabismus was present in 3 patients. (2) The range of ocular movement was normal in 2 patients, nearly normal in 5 and minimally limited in the other 5. (3) Only 1 patient had lateral gaze nystagmus, which was fine and transient. (4) The horizontal saccades were essentially normometric in 11 of the 13 patients, slightly hypometric in 1 and obviously hypometric in 1. These last 2 patients had the second longest and longest EF sizes. The vertical saccades were essentially normometric in 8 of 12 patients, hypermetric in 3, and hypometric in the 1 with the longest EF size. (5) The saccadic velocity in the DM patients was significantly lower than that in the controls in the horizontal or vertical direction, the difference being more prominent in the horizontal direction. (6) The correlation coefficients between horizontal saccadic velocity and EF size, 0.801 (EcoRI) and 0.756 (BglI), had a strong negative correlation (P < 0.01 for both EcoRI and BglI). No statistically significant correlation was found between vertical saccadic velocity (upward and downward) and EF sizes. Although it was difficult to determine whether saccadic slowing was caused by central oculomotor system involvement or extraocular muscle atrophy, the absence of gaze-evoked nystagmus in almost all of the patients favours the latter. Our study shows that neurotological examinations that include a saccadic velocity test are very useful for detecting subtle eye movement abnormalities in DM and for quantitatively evaluating the clinical severity of DM. Received: 7 October 1997 Received in revised form: 10 February 1998 Accepted: 20 March 1998     

Progressive expansion of the myotonic dystrophy CTG repeat in asymptomatic individuals in three successive generations of a family

We report a family in which expansion of CTG repeats was detected in asymptomatic carriers of the myotonic dystrophy allele in three successive generations. PCR-based analysis of the expanded CTG repeat revealed intergenerational amplification of the mutation. We show here that the myotonic dystrophy mutation may remain clinically silent, not only in the oldest generation of a family, but even among siblings and offspring of symptomatic cases. This may represent a mechanism for the maintenance of the myotonic dystrophy gene in the population     

Facial emotion recognition in myotonic dystrophy type 1 correlates with CTG repeat expansion

Objective

To investigate the ability of patients with myotonic dystrophy type 1 to recognise basic facial emotions. We also explored the relationship between facial emotion recognition, neuropsychological data, personality, and CTG repeat expansion data in the DM‐1 group.

Methods

In total, 50 patients with DM‐1 (28 women and 22 men) participated, with 41 healthy controls. Recognition of facial emotional expressions was assessed using photographs of basic emotions. A set of tests measured cognition and personality dimensions, and CTG repeat size was quantified in blood lymphocytes.

Results

Patients with DM‐1 showed impaired recognition of facial emotions compared with controls. A significant negative correlation was found between total score of emotion recognition in a forced choice task and CTG repeat size. Furthermore, specific cognitive functions (vocabulary, visuospatial construction ability, and speed) and personality dimensions (reward dependence and cooperativeness) correlated with scores on the forced choice emotion recognition task.

Conclusion

These findings revealed a CTG repeat dependent facial emotion recognition deficit in the DM‐1 group, which was associated with specific neuropsychological functions. Furthermore, a correlation was found between facial emotional recognition ability and personality dimensions associated with sociability. This adds a new clinically relevant dimension in the cognitive deficits associated with DM‐1.     

Myotonic dystrophy: Correlation of clinical symptoms with the size of the CTG trinucleotide repeat

An unstable DNA sequence of a gene encoding a protein kinase has been identified as the molecular basis of myotonic dystrophy. The correlation between different symptoms of myotonic dystrophy and the size of this unstable base triplet (CTG)_n repeat was investigated in 14 patients. DNA was prepared from whole blood by standard procedures. Detailed clinical, psychological, electrophysiological (quantified measurement of myotonia, electrocardiography) and other laboratory examinations (muscle biopsy in 4 patients, slit lamp examination) were performed. Triplet size correlated significantly with muscular disability and inversely with age at onset of the disease. A greater frequency of mental and gonadal dysfunction could be observed in patients with a larger repeat size. Other symptoms, however, such as cataract, myotonia, gastrointestinal dysfunction and cardiac abnormalities were not correlated with repeat size. Somatic mosaicism with different amplification rates in various tissues might be one possible explanation for the variable phenotypes. Furthermore, other factors such as different expression of the myotonic dystrophy gene might contribute to the clinical variability of the disease at a given triplet size.     

Positive correlation of CTG expansion and pharyngoesophageal alterations in myotonic dystrophy patients

Alteration of the pharyngoesophageal musculature is a common finding in patients with myotonic dystrophy (MD), regardless of the presence of dysphagia. The aim of the present study was to determine whether a specific pattern of swallowing abnormalities could be identified in MD patients, and the possible correlation with the size of CTG repeats. Fifteen MD patients, 8 of whom were asymptomatic for dysphagia, underwent a videofluoroscopic study of swallowing. Alterations of the pharyngoesophageal phase of swallowing were detected in 12 of 15 patients, 6 without clinical evidence of dysphagia. Incomplete relaxation of the upper esophageal sphincter (UES) and esophageal hypotonia were the most common alterations. We found a significant correlation between the number of radiological alterations and the size of CTG repeats. A typical radiological pattern of swallowing has also been identified. The role of videofluoroscopy in evaluation of MD patients is briefly discussed. This paper was supported by the grant n. 1061 from Theleton     

强直性肌营养不良患者及家系成员基因的三核苷酸重复数检测

探讨强直性肌营养不良（ＤＭ）患者及家系成员三核苷酸重复数ＣＴＧ（胞嘧啶、胸腺嘧啶、鸟嘌呤）的变化。方法用聚合酶链反应（ＰＣＲ）扩增及ＤＮＡ杂交法对５例临床诊断ＤＭ患者及其中３个家系的其他１１名成员和１名正常人进行了ＤＭ基因的ＣＴＧ重复数的测定。结果１名正常人ＣＴＧ三核苷酸重复数是３０个，５例ＤＭ病人均在８５个以上，其中２例在１６０５个以上，明显高于正常人ＣＴＧ重复数，而且ＣＴＧ重复数与临床症状轻重有关。１１名家系成员中除２名正常外，余９例ＣＴＧ拷贝数均超过正常范围，此９例据此诊断为ＤＭ。结论ＤＭ基因诊断与其临床诊断相一致，而且该基因诊断可早期发现ＤＭ家系中无临床症状的ＤＭ患者，也可对临床可疑的ＤＭ患者进行鉴别诊断。     

Myotonic dystrophy phenotype without expansion of (CTG)n repeat: An entity distinct from proximal myotonic myopathy (PROMM)?

Myotonic dystrophy (DM) is associated with an expansion of an unstable (CTG)n repeat in the 3' untranslated region of the DM protein kinase (DMPK) gene on chromosome 19q13.3. We studied six patients from two families who showed no expansions of the repeat, in spite of their clinical diagnosis of DM. These patients had multi-systemic manifestations that were distinguishable from those seen in other myotonic disorders, including proximal myotonic myopathy (PROMM). In one additional family, two symptomatic members showed no expanded (CTG)n repeats, while their affected relatives had the expanded repeats. DM haplotype analysis failed to exclude the DMPK locus as a possible site of mutation in each family; however,DMPK mRNA levels were normal. We conclude that a mutation(s) other than the expanded (CTG)n repeat can cause the DM phenotype. The mutation(s) in these families remain(s) to be mapped and characterized.     

Cardiac involvement and CTG expansion in myotonic dystrophy

Although cardiac complications are well known in myotonic dystrophy (DM), patients rarely manifest symptoms of cardiac disease, and if so they most often show conduction abnormalities or arrhythmia. In this study, specific cardiac findings were reviewed in 79 patients with DM. No correlation was found between the cardiac assessments and the CTG expansion. Thus, for a single patient the cardiac involvement in the disease can not be predicted from the findings of the genetic investigation. On the other hand, a clear positive relationship of the PR interval with the QRS duration was revealed, as well as a positive correlation between the age of the DM patient and the QRS duration, which increases with 0,54 ms/year. Systolic dysfunction, evaluated by transthoracic echocardiography, seems to be quite uncommon. In 32 % of the patients with a normal ECG, the 24 h Holter monitoring showed arrhythmias and conduction abnormalities. Based on these findings we recommend a follow up of DM patients not only based on the ECG, but also through 24 h Holter monitoring. Received: 27 June 2001, Received in revised form: 16 October 2001, Accepted: 23 October 2001     

强直性肌营养不良症患者的CTG重复次数与心电图改变的关系

目的 研究强直性肌营养不良（ＤＭ）症患者的肌强直蛋白激酶（ＭＴＰＫ）基因中胞嘧啶、胸腺嘧啶、鸟嘌呤（ＣＴＧ）三核苷酸重复次数与ＤＭ病人心电图改变的关系。方法 经临床及用长模板扩增＾ＴＭＰＣＲ法对３个ＤＭ家系共３７个受检者进行基因检测,同时作心电图记录。结果 ２５例确诊为ＤＭ患者;１例可疑;余１１名家系成员属ＭＴ家系正常人。ＤＭ病人心电图异常率为８０％,而ＤＭ家系正常人心电图异常率仅为９％,两者有明     

Relation of CTG expansion and clinical variables to electrocardiogram conduction abnormalities and sudden death in patients with myotonic dystrophy

We prospectively followed 63 patients with myotonic dystrophy (DM) after establishing diagnosis of DM for an average 8 years in an attempt to detect conduction disturbances (by electrocardiography and/or Holter monitoring) and sudden cardiac events (sudden death, cardiac syncope) and correlate them to potential predicting factors (CTG repeat expansion in the myotonin protein kinase gene and several clinical variables: clinical type and duration of DM, age and sex). Twenty-six patients developed conduction disturbances, five patients died suddenly, and two patients experienced cardiac syncope necessitating urgent implantation of pacemaker. Analysis showed no significant correlation between conduction disturbances and/or cardiac events and CTG expansion. Furthermore, no correlation was found with type of DM, whereas conduction disturbances and sudden cardiac events correlated with patients' age, duration of disease and male sex. Results on our cohort of DM patients show that CTG expansion has no role in predicting neither conduction abnormalities nor sudden death. It seems that risk of sudden death increases with duration of disease and age, and that risk is higher in male patients.     

Developmental expression of myotonic dystrophy protein kinase in brain and its relevance to clinical phenotype

To investigate the pathophysiologic role of myotonic dystrophy protein kinase (DMPK) in the brain in myotonic dystrophy (MD), the developmental characteristics of DMPK immunoreactivity in the central nervous system and its alteration with disease were studied. Eleven patients’ brain with MD (5 congenital form, 6 adult form) were examined by immunohistochemistry using a specific antibody against synthetic DMPK peptides, anti-peptide DM1, and compared with 30 control brains, including 16 age-matched controls. In controls, DM1-immunoreactive neurons appeared in the early fetal frontal cortex and cerebellar granule cell layer, persisting through 29 weeks of gestation and then disappearing. In contrast, immunoreactive neurons continued to persist in the cerebral cortex and cerebellar granule cell layer of MD patients. When we counted DM1-immunoreactive neurons, the increase over controls was greater in the congenital form of MD than in the adult form, and was greater in the cerebrum than in the cerebellum in both forms of MD. DM1 immunostaining was predominantly nuclear, mirroring Western blotting of subcellular fractions. Differences in DM1 expression related to development and to the two forms of MD may be closely related to the pathogenesis of mental retardation in this disease. Received: 30 July 1999 / Revised: 21 January 2000 / Accepted: 1 February 2000     

Scaled-down genetic analysis of myotonic dystrophy type 1 and type 2

Types 1 and 2 myotonic dystrophy are neuromuscular disorders caused by genomic expansions of simple sequence repeats. These mutations are unstable in somatic cells, which leads to an age-dependent increase of expansion length. Studies to determine whether changes in repeat size may influence disease severity are limited by the small amount of DNA that can be recovered from tissue biopsies samples. Here we used locked nucleic acid oligonucleotide probes and rolling circle amplification to determine length of the expanded repeat in sub-microgram quantities of genomic DNA. These methods can facilitate genetic analysis in cells and tissues obtained from individuals with myotonic dystrophy.     

DM基因CTG重复数与BAEP、SEP、VEP对比分析

目的：探讨强直性肌营养不良（DM）患者及其家系成员三核苷酸重复数CTG（胞嘧啶、胸腺嘧啶、乌嘌呤）的变化与脑干听觉诱发电位（BAEP）、体感诱发电位（SEP）、视觉诱发电位（VEP）的关系。方法：用聚合酶链（PCR）扩增及DNA杂交法对5例临床诊断DM患者及其中三个家系的16名成员进行DM基因的CTG重复数和BAE、SEP和VEP测定。结果：10名正常人CTG重复数是30个,BAEP、SEP、VEP正常;5例DM病人CTG重复数均在85个以上,其中2列在1605个以上,明显高于正常人;16例家系成员中除4例正常,余12例CTG重复数均超过正常基因,而且,CTG重复数与临床症状、BAEP、SEP、VEP轻重有关。结论DM基因诊断有其临床症状、BAEP、SEP、VEP改变相一致。     

Myasthenia gravis and thymoma coexisting with myotonic dystrophy type 1

We describe a 34-year old man presenting with subacute generalized myasthenic symptoms. His clinical features and laboratory investigations demonstrated both myasthenia gravis and myotonic dystrophy type 1. The computerized tomography of chest revealed anterior mediastinal mass. The lymphocyte-rich thymoma was removed surgically and he received radiotherapy. Recent observations suggested that the patients with myotonic dystrophy may have an increased risk of benign and malignant tumours but its coexistence with thymoma is very rare. The risk of thymoma associated with myotonic dystrophy is unknown.     

Correlation between distribution of muscle weakness,electrophysiological findings and CTG expansion in myotonic dystrophy

Myotonic dystrophy type 1 (DM-1) is a multi-system disorder affecting the muscles, brain, cardiovascular system, endocrine system, eyes and skin. Diagnosis is made by clinical, electrodiagnostic and genetic studies. This study aimed to determine the correlation between CTG expansion and distribution of muscle weakness and clinical and electrophysiological findings. Genetically confirmed DM-1 patients presenting to Shariati Hospital between 2005 and 2011 were included in this study. Clinical, electrodiagnostic and genetic testing was performed and the correlation between CTG expansion and distribution of muscle weakness and clinical and electromyographic findings was studied. Thirty-three genetically confirmed DM-1 patients were enrolled. Myotonia, bifacial weakness and distal upper limb weakness were seen in all patients. Diabetes mellitus was found in one patient (3%), cardiac disturbance in eight (24.2%), cataracts in eight (24.2%), hypogonadism in five (15.2%), frontal baldness in 13 (39.4%), temporalis wasting in 14 (42.4%), temporomandibular joint disorder in seven (21.2%) and mental retardation in eight (24.2%). The mean number of CTG repeats, measured by Southern blot, was 8780 (range 500–15,833). A negative correlation was found between CTG expansion and age of onset. Temporalis wasting and mental retardation were positively correlated with CTG expansion. No relationship was found between weakness distribution, electromyographic findings, other systemic features and CTG expansion. In this study of DM-1 in Iran, we found a correlation between CTG expansion and age of onset, temporalis wasting and mental disability. No correlation between CTG expansion and electrodiagnostic and other clinical findings were detected.