Abstract
Background: Myotonic dystrophy types 1 (DM1) and 2 (DM2/proximal myotonic myopathy PROMM) are dominantly inherited disorders with unusual multisystemic clinical features. The authors have characterized the clinical and molecular features of DM2/PROMM, which is caused by a CCTG repeat expansion in intron 1 of the zinc finger protein 9 (ZNF9) gene.
Methods: Three-hundred and seventy-nine individuals from 133 DM2/PROMM families were evaluated genetically, and in 234 individuals clinical and molecular features were compared.
Results: Among affected individuals 90% had electrical myotonia, 82% weakness, 61% cataracts, 23% diabetes, and 19% cardiac involvement. Because of the repeat tract’s unprecedented size (mean ∼5,000 CCTGs) and somatic instability, expansions were detectable by Southern analysis in only 80% of known carriers. The authors developed a repeat assay that increased the molecular detection rate to 99%. Only 30% of the positive samples had single sizeable expansions by Southern analysis, and 70% showed multiple bands or smears. Among the 101 individuals with single expansions, repeat size did not correlate with age at disease onset. Affected offspring had markedly shorter expansions than their affected parents, with a mean size difference of −17 kb (−4,250 CCTGs).
Conclusions: DM2 is present in a large number of families of northern European ancestry. Clinically, DM2 resembles adult-onset DM1, with myotonia, muscular dystrophy, cataracts, diabetes, testicular failure, hypogammaglobulinemia, and cardiac conduction defects. An important distinction is the lack of a congenital form of DM2. The clinical and molecular parallels between DM1 and DM2 indicate that the multisystemic features common to both diseases are caused by CUG or CCUG expansions expressed at the RNA level.
Myotonic dystrophy type 2 (DM2) is an autosomal-dominant, multisystemic disease. In 1998 we mapped the disease locus to 3q211 and recently demonstrated that DM2 is caused by the expansion of a CCTG repeat located in intron 1 of the zinc finger protein 9 (ZNF9) gene.2 In Europe, the disease in these families has been called proximal myotonic myopathy (PROMM)3 or proximal myotonic dystrophy (PDM).4 In the United States these families were described as having “myotonic dystrophy with no CTG repeat expansion”.5,6⇓
The discovery of the tetranucleotide CCTG expansion for the first time allows definitive molecular testing for DM2. We screened a large panel of European and American families that during the previous 8 years were suspected of having PROMM or DM2 based on clinical criteria. We describe an improved method for detecting the DM2 expansion and report the features of 379 individuals with genetically confirmed DM2. Defining the clinical features of DM2 in a large group of genetically confirmed patients should be helpful for future patient management. In addition, comparing the extent of the clinical similarities and distinctions between DM1 and DM2 has important implications for understanding the molecular pathogenesis of these diseases.
Methods.
Family identification and clinical studies.
A large number of families and single patients have been seen in Germany and Minnesota with undiagnosed myopathies suspected of being DM2/PROMM. DNA samples from these patients have been stored with the patients’ informed consent for possible future diagnostic research. Patients and additional family members who agreed to participate had blood drawn and underwent neurologic examinations. Many of the interviews and examinations took place in patient homes. Although not actively recruited, 12 DM2-positive family members younger than 21 years also participated. Clinical and genetic data are reported for 234 individuals, some of whom were summarized previously;2 genetic information is included for an additional 145 individuals for whom detailed clinical information was not available. The study was done with the approval of the Institutional Review Boards/Ethics Committee at the Universities of Minnesota and Würzburg.
Electrophysiological assessment was done with portable equipment. Ophthalmologic examination of the American patients was performed in the field with direct ophthalmoscopy; a limited number of patients underwent slit lamp examination in ophthalmology clinics. Muscle biopsies were taken from 42 clinically affected patients. The specimens were quick-frozen, sectioned, and stained with hematoxylin and eosin for most results reported; fiber types were identified by ATPase staining at different pH values. Studies were performed over a period of 10 years with additional testing included as our understanding of the disease evolved. Clinical results are reported as percentages of individuals tested for each specific feature.
Age at onset was determined by either the patient’s recollection of the age at which the first symptom of the disease occurred or the age of diagnosis for patients unaware of their disease. An extended discussion on the potential bias with using this estimate has been published in a previous report.7 Ages at onset between parent–offspring pairs were compared using a paired two-tailed t-test.
Genetic methods.
PCR amplification across the DM2 CCTG repeat was performed as previously described.2 Genomic Southern analysis was done using DNA digested with either BsoBI or EcoRI. To improve detection of the DM2 expansion we developed a repeat assay (RA) based on previously published methods for DM1 and SCA-10.8,9⇓ The RA amplifies the genomic DM2 region containing the CCTG repeat expansion, using primers CL3N58-D R (5′-GGCCTTATAACCATGCAAATG-3′), JJP4CAGG(5′-TACGCATCCGAGTTTGAGACGCAGGCAGGCAGGCAGGCAGG-3′), and JJP3 (5′-TACGCATCCGAGTTTGAGACG-3′), followed by Southern analysis of the PCR products probed with an internal probe. Detailed methods for the RA are online (see the supplementary material on the Neurology Web site; go to www.neurology.org).
The monozygosity of the twins was confirmed by analysis of the genotypes of six short tandem repeat markers from different chromosomes, as previously described (p < 0.001).2
Results.
Molecular diagnostics.
The unprecedented size and somatic instability of the DM2 expansion complicate molecular testing and the interpretation of genetic test results (figure 1). Outlined below is a description of three steps involved in the molecular detection of the DM2 expansion and the types of data obtained by PCR, Southern analysis, and the RA (see Methods).
Figure 1. Molecular diagnosis of DM2. (A) PCR analysis of the CL3N58 marker. The genotype of each individual is shown in base pairs. Alleles too large to amplify by PCR, which are referred to as “blank alleles,” are indicated by a “B” and make the segregation of the markers appear non-Mendelian. (B) Expansion detection by genomic Southern analysis. DM2 Southern analysis of genomic DNA from control (N), affected individuals with a detectable (A) and nondetectable (A*) expanded allele is shown (Lanes 1–7). In contrast to DM2, an SCA8 Southern (Lane 8) shows equally intense signals for the normal and expanded alleles. (C) Schematic diagram of the PCR-based RA. The straight arrow represents the flanking primer CL3N58-D R. Tailed arrows represent the JJP4CAGG primer. A third primer (JJP3, not shown), used to make the PCR reaction more robust, has the same sequence as the hanging tail of JJP4CAGG. The primer used to probe Southern blots of the PCR products is CL3N58-E R. (D) Repeat assay results. RA results for affected individuals with expansions that were detected (A) or not detected (A**) by genomic Southern analysis and are shown in Lanes 1 to 5 and 8. Negative results from unaffected controls (N) are shown in Lanes 6,7,9, and 10.
Step 1: PCR analysis.
Because DM2 expansions are too large to amplify by PCR, all expansion-positive individuals appear to be homozygous and thus indistinguishable from the 15% of unaffected controls who are truly homozygous. Family studies can distinguish true homozygotes from expansion carriers (figure 1A) because affected children often do not appear to inherit an allele from their affected parent. We refer to this apparent non-Mendelian inheritance pattern, which is caused by the failure of the expanded allele to amplify, as the presence of a “blank allele.” Demonstration of a blank allele provides strong evidence that a family carries a DM2 expansion but can also occur in cases of misattributed paternity.10
Step 2: Southern analysis.
Because of the size (mean ∼5,000, range 75 to >11,000 CCTG repeats) and somatic instability of the DM2 repeat, genomic Southern analyses fail to detect expansions in 20% of known carriers (table 1). Expanded alleles when detected can appear as single discrete bands, multiple bands, or smears (figure 1B). Compared to other expansion disorders, such as SCA8 (figure 1B, lane 8), in which the expanded and normal alleles are equally intense, detectable DM2 expansions are almost always less intense than the normal alleles. This intensity difference indicates that even when a proportion of the expanded allele creates a discrete visible band, the rest of the expanded allele varies markedly in size within blood and migrates as a diffuse undetectable smear.
Table 1 Molecular diagnostic sensitivity to DM2
Step 3: Repeat assay.
To detect the presence of DM2 expansions in individuals with inconclusive Southern blots, we used the RA (see Methods). By using a PCR primer that primes from multiple sites within the elongated CCTG repeat tract, our RA can be used to detect DM2 expansions by the presence of a smear of products with molecular weights higher than in control lanes (figure 1C and D). Although the RA reliably identifies the presence or absence of the DM2 expansion, it cannot be used to determine repeat size. To insure specificity, RA PCR products are transferred to a nylon membrane and probed with an internal oligonucleotide probe; there were no false-positives among 320 control chromosomes. Probing with an internal primer is critical for avoiding false-positives; there was a 21% false-positive rate when the RA PCR products were simply visualized by ultraviolet light after staining with ethidium bromide. False-positive, high molecular weight products were also detected when the RA PCR products were run on an ABI 3100 machine (Applied Biosystems, Inc., Foster City, CA). When performed as we describe (Methods), the RA is both sensitive and specific, increasing the detection rate of DM2 expansions from 80% by genomic Southern analysis alone to 99% for a panel of known expansion carriers (see table 1).
Pedigree examples of instability.
The pedigree shown in figure 2 illustrates the diagnostic challenges and the types of repeat instability that are typical in a DM2 family. “Blank alleles” that failed to amplify due to a CCTG expansion are indicated by a “B.” There is marked variation in intergenerational repeat sizes. For example individual III-7 has a smaller expansion than her affected parent, which is larger in one of her children (IV-1) and smaller in the other (IV-2). The extreme somatic instability is illustrated by monozygotic twins III-1 and III-2, with expansion sizes that differ in size by 11 kb (2,750 CCTGs). Some family members have single discrete expansions, but many others have multiple expansions or diffuse bands. An example of the utility of the RA is demonstrated by individual II-5, who was RA-positive but negative by Southern analysis.
Figure 2. Abbreviated pedigree of a DM2 family: Solid symbols represent affected individuals. Although sex of the youngest generation shown for various branches of the family has been changed to insure confidentiality, the sex of transmitting parents was not changed so that information about how sex influences repeat size in subsequent generations is preserved. Information below each symbol includes age at blood draw; CL3N58 PCR allele sizes (“B” indicates a nonamplifying blank allele); and either the size of the expansion(s) detected by Southern (in kb) or repeat assay results (RA+ or RA−) for those with no expansion on Southern analysis. The RA was positive for all individuals with positive Southern results (not shown).
DM2-positive patients and families.
We have identified 379 DM2 positives from 133 families by using Southern and RA analyses. Most families could trace an affected ancestor to Germany or Poland, and all were of European descent. As expected for a dominantly inherited disease, approximately 50% of adults at first-degree risk for DM2 were affected. The higher number of affected women compared to men in our study (210 vs 169) is consistent with the higher rate of female participation (420 vs 332 males). The age of DM2-positive subjects when examined ranged from 8 to 85 with a mean of 47 years.
Clinical features.
The clinical features of the DM2 expansion positive patients are described below for the 234 affected subjects whom we had examined.
Muscle symptoms and signs.
Muscle symptoms (pain, stiffness, myotonia, and weakness) are the most common symptoms reported in adult DM2 subjects of all ages (table 2). Fluctuating or episodic muscle pain is frequent in DM2 (63% in those >50 years). The characteristic pattern of muscle weakness involves neck flexors, elbow extensors, thumb and deep finger flexors, and hip flexors and extensors. Facial and ankle dorsiflexor weakness is less common. Thirty percent of the subjects reported symptomatic hip muscle weakness that developed after age 50. In DM2/PROMM patients who come to medical attention because of muscle pain, stiffness, or myotonia prior to developing symptomatic weakness, manual strength testing is frequently abnormal in neck flexors and deep finger and thumb flexors, suggesting that these are the muscle groups affected the earliest. Though rarely severe, muscle atrophy was recorded in 9% of subjects.
Table 2 Clinical features of DM2 and DM1
Muscle biopsies.
Muscle biopsies from 42 DM2 patients (18 to 73 years, mean 50 years) had many of the same histologic features that are found in DM1 biopsies, with a high percentage of fibers having centrally located nuclei sometimes occurring in chains, angulated atrophic fibers sometimes occurring in groups, severely atrophic fibers with pyknotic nuclear clumps (“nuclear clumps” in table 2), hypertrophic fibers, occasional necrotic fibers, fibrosis, and adipose deposition. There was no consistent abnormality of fiber type distribution, with two biopsies having mild type 1 predominance and two having mild type 2 predominance. Atrophic angulated fibers of both fiber types, as determined by ATPase staining, were evident in most biopsies. Most biopsies were of vastus lateralis and were abnormal despite manual strength testing being normal for that muscle; two biopsies were normal (biceps brachii, 18 and 26 years), and three had only increased central nuclei (biceps brachii 39 years, and vastus lateralis 30 and 36 years).
Cataracts.
The posterior subcapsular iridescent cataracts are identical in DM1 and DM2 patients.11 Cataracts needed to be extracted in 75 individuals at ages ranging from 28 to 74 years. Among 10 genetically positive subjects under 21 years, cataracts were present in 2 by slit lamp examination, indicating that this is a prominent and early feature of the disease. Cataracts detected by ophthalmoscopy typically develop in the third to fifth decades of life, with slit lamp demonstrating cataracts in 2 of 10 subjects in the second decade.
Cardiac features.
Cardiac complaints include frequent palpitations, intermittent tachycardia, and episodic syncope, with syncopal spells reported in 18 (8% of the entire panel of 234 subjects). These symptoms increase in frequency with age (see table 2). Cardiac conduction abnormalities were seen in 20% of patients (9 of 44), either atrioventricular (11%) or intraventricular (11%) blocks. DM2 patients can develop unexpected fatal arrhythmias. A history of progressive cardiomyopathy, in the absence of overt myocardial ischemia or other obvious causes, was found as a potentially life-threatening condition in 7 of 100 DM2 patients over 50 years.
Serologic and other changes.
Laboratory results from 150 patients showed elevated serum CK, typically less than five times the upper limits of normal, and elevated gamma-glutamyltransferase. Additional serologic testing on 20 patients showed low IgG and IgM but normal IgA, the same pattern that is seen in DM1.11 Primary male hypogonadism was present in the majority (17 of 26) of the men serologically tested for testicular function, with elevated follicle-stimulating hormone (FSH), low or low-normal testosterone levels, and oligospermia. By history, diabetes was present in 23% (n = 79), with glucose tolerance testing showing insulin insensitivity (elevated basal insulin levels or prolonged insulin elevation, n = 16) in 75%. Age-independent hyperhydrosis is reported by 20% to 30% of patients, and early-onset male frontal balding is observed in approximately 20% of German and 50% of American men aged 21 to 34 years.
Age at onset and disease progression.
Patients reported that they remembered first symptoms of disease to have occurred from ages 13 to 67 (median = 48 years, mean ± SD = 37 ± 15). Table 3 details the initial symptom and age at onset for the 209 individuals in whom symptomatic onset was reported to have occurred prior to enrollment in the study. Subjects younger than 21 years were not recruited and are not included in table 2, but 12 genetically confirmed family members in this age group participated voluntarily (range = 8 to 20 years, mean = 16); none had muscle weakness, cardiac symptoms, diabetes, or visual impairment from cataracts, but 3 reported muscle pain and symptoms of myotonia, and 1 had hyperhydrosis. Consistent with a previous study7 there is strong statistical evidence (p < 1 × 10−14) for earlier ages at onset among offspring of affected individuals (−13 years, n = 79 parent-offspring pairs).
Table 3 Identification of initial symptom and age at onset
Lack of congenital DM2 and aspects of disease severity.
We did not observe any congenital DM2 patients among our large group of families, and there was no evident relationship between DM2 and mental retardation. Some affected women had recurrent spontaneous abortions, although it is not clear whether DM2 leads to higher than normal rates of spontaneous abortion, nor does it lead to higher than normal rates of hydramnios, or still birth, all of which occur at markedly increased frequency in DM1.11 Some women experienced an increase of myotonic stiffness during pregnancy, but DM2 did not seem to cause any problems of delivery. We did not encounter DM2 patients who had experienced problems during general anesthesia.
Clinical and molecular correlations.
An unusual feature of the DM2 expansion is that repeat size is positively correlated with the age at which the blood is drawn (figure 3A, r2 = 0.19, p = 4.6 × 10−6, n = 101). The fact that the repeat tracts expand as an individual gets older complicates any analysis of the effects of repeat length on age at onset. Correlations of repeat size with various measures of disease onset are shown in figure 3, B through D using the subset of individuals with single measurable bands on Southern analysis. Positive correlations (i.e., smaller repeats associated with earlier age at onset) were found for repeat size versus both age at onset of the initial symptom (r2 = 0.07, p = 1.3 × 10−2, n = 93), and age at onset of weakness (r2 = 0.28, p = 8.8 × 10−6, n = 63). No significant correlation was observed between repeat size and age at cataract extraction (n = 29). The apparent positive correlation between repeat length and age at onset was unexpected because in other microsatellite expansion disorders there is a negative correlation, with larger expansions associated with earlier ages at onset. To determine if the positive correlations we observed could simply reflect the fact that repeat length increases with age, multivariate analysis was performed. These results indicate that the effect of the age at which the blood sample was drawn explained nearly all (>99%) of the apparent correlation between repeat length and age at symptom onset.
Figure 3. Correlation of repeat length with clinical severity. Among individuals with single sizable expansions correlations between the repeat size and (A) age at the time the blood sample was drawn; (B) age at onset of initial symptom; (C) age at onset of weakness; and (D) age at initial cataract extraction are shown. In contrast to DM1 and other microsatellite disorders, longer DM2 repeat tracts are not correlated with earlier onset of disease.
Although complicated by both somatic instability and the increase in repeat length with age, we determined intergenerational differences in repeat for 25 parent–child pairs, the subset of affected individuals in which both the parent and child had single bands on Southern analysis (figure 3A). In 23 of 25 transmissions we observed smaller repeat lengths in the younger generation, with a mean change of −17 kb (−4,250 CCTG repeats). In one instance the repeat size was 38 kb smaller in the affected child (−9,500 CCTG repeats). There were apparent size increases in two transmissions (+1 and +8 kb). These apparent intergenerational changes in repeat length are much greater for DM2 than for any other microsatellite disorder (figure 4B). No differences in degree or direction of intergenerational changes were seen in male versus female transmissions.
Figure 4. Intergenerational repeat instability. (A) Repeat lengths of 25 affected parent–child pairs from a subset of individuals in which both the parent and child had single bands on Southern analysis are shown. (B) The relative repeat size differences among parent–offspring pairs in DM2 patients is compared with those observed for the polyglutamine (poly Q) diseases and DM1.
Discussion.
Defining the clinical features of DM2 has important implications for understanding the molecular mechanisms of DM pathogenesis. This study demonstrates that DM2 closely resembles adult-onset DM1, with common features including progressive weakness, myotonia, disease-specific muscle histology, cardiac arrhythmias, iridescent cataracts, male hypogonadism, insulin insensitivity, and hypogammaglobulinemia. These similarities are the main reason why DM2/PROMM had not been delineated before genetic testing became available.3,5⇓ Despite the striking similarities of DM2 and DM1 as multisystemic disorders, there are important differences. One clear distinction is the absence of a congenital form of DM2. In DM1, longer repeats are often associated with severe neonatal weakness, mental retardation, and skeletal abnormalities; to date, no comparable cases of DM2 have been reported despite the fact that DM2 expansions are typically much larger than the DM1 expansions associated with congenital cases. Other differences of DM2 include an apparent lack of mental retardation in juvenile cases; less evident central hypersomnia; less symptomatic distal, facial, and bulbar weakness; and less pronounced muscle atrophy.
DM1 individuals often come to medical attention because of the mental retardation or disabling distal weakness and myotonia, but DM2 patients typically first seek medical evaluation because of muscle pain, stiffness, fatigue, or when they develop proximal lower extremity weakness. Although some DM2 features are milder than in DM1 (clinical myotonia, distal and facial weakness), others are comparable in presentation (cataracts, hypogonadism, and insulin insensitivity). We have seen a progressive cardiomyopathy that appears to be a consequence of DM2, although specific investigation of this point is necessary. DM2 patients often seek medical attention for isolated symptoms of the disease, without being aware of their complex underlying disorder. A genetic diagnosis of DM2 will improve patient care by facilitating better monitoring of the diverse clinical features known to be part of the disease, including early onset cataracts, diabetes, testicular failure, and cardiac arrhythmias.
We have identified 379 DM2-positive individuals from 133 families, indicating that DM2 is not rare in populations of northern European ancestry. In Germany DM2 may be as common as DM1.12 Because DM1 families often come to the attention of physicians when a child is severely affected, the lack of congenital DM2 may explain its apparent underdiagnosis. All three of the original families described with PROMM3 and 11 of the 14 subsequently described PROMM families have the DM2 expansion (families 7, 12 ,and 13 from Ricker et al.12 had features of PROMM/DM2 that with additional investigation did not cosegregate in the individual families). In addition, other PROMM families initially reported to have been excluded from the DM2 locus by linkage analysis13,14⇓ have now been shown to be DM2 positive. These data indicate that families previously described with PROMM or DM2 have the same clinical disorder caused by the DM2 CCTG expansion on chromosome 3. Contrary to earlier views, analysis of our large collection of families has not revealed any convincing examples that would suggest the existence of a third mutation that causes a similar dominantly inherited multisystemic myotonic disorder, i.e., DM3.
The DM2 expansion has several novel molecular features including: (1) it is the first pathogenic tetranucleotide expansion; (2) expansions are larger than reported in any other disease (more than 44 kb in DM2 versus 12 kb in DM1); and (3) the degree of somatic heterogeneity of the repeat expansion is unprecedented. In other expansion disorders, Southern analysis (figure 1B) can reliably confirm the presence of expansions too large to amplify by PCR.15-20⇓⇓⇓⇓⇓ In contrast, for DM2 the heterogeneity of repeat sizes in blood is so extreme that approximately one of five of the expansions are not detectable by Southern analysis, which causes a diagnostic challenge not previously encountered, even among disorders with large expansions such as DM1, SCA8, and SCA-10. Although the somatic heterogeneity complicates the molecular diagnosis of DM2, the RA described here improved detection to 99%.
In other reported microsatellite expansion disorders larger repeat expansions are associated with earlier onset and increased disease severity.21 Although anticipation has been reported in DM2/PROMM families based on clinical criteria,7 and earlier ages at onset in offspring of affected parents was found in this study, the expected trend of longer repeat expansions in patients with earlier ages at onset was not observed, so the explanation of the observed intergenerational changes remains unclear. The somatic heterogeneity of the repeat, and the fact that the size of the repeat increases with age, complicate this analysis and may mask meaningful biologic effects of repeat size on disease onset and severity. However, it is also possible that expansions over a pathogenic size threshold exert similar effects regardless of how large they become, or even that smaller repeats are more pathogenic than larger repeats. In adult-onset DM1, the most significant correlations between repeat length and disease onset are for repeats less than 400 CTGs.22 Another unusual molecular feature of DM2, the tendency of repeats to be shorter in offspring after both maternal and paternal transmission, may in part reflect increases in repeat size with age, but the overall cause and biologic significance of this observation are yet to be determined.
DM2 provides an opportunity to better understand the pathogenic mechanisms of DM. Our cloning and characterization of the DM2 mutation revealed that the DM2 mutation, like that of DM1, involves a similar microsatellite motif (CCTG and CTG, respectively). Both mutations are transcribed into RNA but not translated and accumulate as nuclear RNA foci. These molecular parallels, combined with the clinical parallels, indicate that the repeat expansions expressed at the RNA level cause the multisystemic features common to both diseases.2 Intranuclear RNA foci in both DM1 and DM2 bind specific RNA binding proteins,23-25⇓⇓ and the repeat expansions in both diseases alter splicing of the insulin receptor and chloride channel transcripts. Changes in the insulin receptor splicing lead to insulin insensitivity and a predisposition to diabetes,26,27⇓ and alterations in chloride channel splicing lead to a loss of chloride channel protein that results in electrical myotonia.28,29⇓ These changes in RNA binding proteins and the alteration in gene splicing provide a convincing model of how untranslated repeat expansions in RNA can cause the multisystemic features common to both forms of myotonic dystrophy.
Although DM2 has many of the clinical features found in adult-onset DM1 patients, DM2 does not involve some of the changes seen in the early onset or congenital forms of DM1. Defining the pathophysiological differences between DM1 and DM2, which could involve spatial and temporal expression differences between the two repeat-containing transcripts, the regulation of locus specific genes such as DMPK, SIX5, or ZNF9 and/or downstream RNA effects of the CUG or CCUG expansions, will be important for understanding the clinical differences.2 Fillipova et al. have suggested that methylation at the DM1 locus in congenital cases could increase expression of the CUG-containing transcripts.30 Although the etiology of the congenital form of DM1 remains enigmatic, Occam’s razor suggests that the simplest model of DM pathogenesis is that pathogenic effects of RNAs containing the CUG and CCUG expansions cause the multisystemic features common to DM1 and DM2.
Acknowledgments
Supported by the University of Minnesota General Clinical Research Center (MO1-RR00400), the Förderverein of the Department of Neurology, University of Würzburg, the Muscular Dystrophy Association USA, and the National Institutes of Health (NS35870).
Acknowledgment
The authors thank the DM2 families for participating; Melinda Moseley, Christina Liquori, Marcy Weatherspoon, Jeff Lande and Stephen Tapscott for helpful discussions; Helly Ricker for her constant clinical and financial help in visiting patients; Klaus Toyka for critically reading the manuscript; and the following European neurologists for providing contact to affected families: M. Auer-Grumbach, U. Besinger, P. Broich, D. Claus, R. Dengler, U. Dillmann, K. F. Druschky, A. Ferbert, J. Forster, F. Glötzner, A. Gonschorek, J. G. Heckmann, H. C. Hopf, R. W. C. Janzen, E. Kuhn, H. Kwiecinski, H. P. Ludin, P. Marx, H. M. Meinck, H. Müller-Vahl, W. Paulus, D. Pongratz, J. Priller, C. D. Reimers, R. Rohkamm, B. Schalke, B. Schrank, R. Schröder, G. Schwendemann, W. Schulte-Mattler, W. Steinke, G. Stoll, S. Vielhaber, P. Vieregge, P. Vogel, M. Vorgerd, T. Witt, S. Zierz.
Footnotes
-
Additional material related to this article can be found on the Neurology Web site. Go to www.neurology.org and scroll down the Table of Contents for the February 25 issue to find the title link for this article.
- Received August 22, 2002.
- Accepted November 19, 2002.
References
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