Myotonic dystrophy type 2: molecular, diagnostic and clinical spectrum

[Musculoskeletal pain as the most prominent feature in myotonic dystrophy type 2]

BACKGROUND

Myotonic dystrophy type 2/proximal myotonic myopathy (DM 2/PROMM) is an autosomal dominant multisystem disorder characterized by proximal muscle weakness, myotonia and musculoskeletal pain.

PATIENTS AND METHODS

We describe five patients with DM 2/PROMM in whom musculoskeletal pain was the most prominent feature. We used the McGill Pain Questionnaire for standardized pain assessment.

RESULTS

The patients reported multiple types of musculoskeletal pain including tenderness, cold-enhanced and exercise-related musculoskeletal pain. Exercise-induced or -enhanced musculoskeletal pain was indicated as the most disabling feature.

CONCLUSIONS

Myotonic dystrophy type 2 should be considered as one of the differential diagnoses in patients with musculoskeletal pain. Family history and laboratory tests provide critical diagnostic clues.

Reduction of the rate of protein translation in patients with myotonic dystrophy 2

Myotonic dystrophy 2 (DM2) is an autosomal dominant, multisystem disease, which primarily affects skeletal muscle. DM2 is caused by CCTGn expansion in the intron 1 of the ZNF9 gene. Expression of the mutant CCUGn RNA changes RNA processing in patients with DM2; however, the role of ZNF9 protein in DM2 pathology has been not elucidated. ZNF9 has been shown to regulate cap-dependent and cap-independent translation. We have examined a possible role of ZNF9 in the regulation of translation in DM2 patients. We found that ZNF9 interacts with the 5' UTRs of terminal oligopyrimidine (TOP) tract mRNAs encoding human ribosomal protein, RPS17, poly(A)-binding protein 1 (PABP1), and the elongation factors, eEF1A and eEF2. The binding activity of ZNF9 toward these TOP-containing 5' UTRs is reduced in DM2 muscle. Consistent with the reduction of this activity, the levels of RPS17, PABP, eEF1A, and eEF2 proteins are also diminished in DM2 muscle. The reduction of ZNF9 RNA-binding activity in DM2 correlates with a decrease of ZNF9 protein levels in cytoplasm of DM2 muscle cells. We found that the reduction of ZNF9 is caused by expression of the mutant CCUG repeats. This decrease of proteins of translational apparatus in DM2 correlates with a reduction of a rate of protein synthesis in myoblasts from DM2 patients. We found that the ectopic expression of ZNF9 in DM2 myoblasts corrects rate of protein synthesis, suggesting that the alterations in CCUG-ZNF9-TOP mRNAs pathway are responsible for the reduction of the rate of protein translation in DM2 muscle cells.

Expression of RNA CCUG repeats dysregulates translation and degradation of proteins in myotonic dystrophy 2 patients

Myotonic dystrophy 2 (DM2) is a multisystem skeletal muscle disease caused by an expansion of tetranucleotide CCTG repeats, the transcription of which results in the accumulation of untranslated CCUG RNA. In this study, we report that CCUG repeats both bind to and misregulate the biological functions of cytoplasmic multiprotein complexes. Two CCUG-interacting complexes were subsequently purified and analyzed. A major component of one of the complexes was found to be the 20S catalytic core complex of the proteasome. The second complex was found to contain CUG triplet repeat RNA-binding protein 1 (CUGBP1) and the translation initiation factor eIF2. Consistent with the biological functions of the 20S proteasome and the CUGBP1-eIF2 complexes, the stability of short-lived proteins and the levels of the translational targets of CUGBP1 were shown to be elevated in DM2 myoblasts. We found that the overexpression of CCUG repeats in human myoblasts from unaffected patients, in C2C12 myoblasts, and in a DM2 mouse model alters protein translation and degradation, similar to the alterations observed in DM2 patients. Taken together, these findings show that RNA CCUG repeats misregulate protein turnover on both the levels of translation and proteasome-mediated protein degradation.

Myotonic dystrophy type 2 with focal asymmetric muscle weakness and no electrical myotonia

Genetically proven myotonic dystrophy type 2 (DM2) was found in a 61-year-old woman with creatine kinase (CK) elevation and only isolated weakness of one triceps. There was no clinical or electrical myotonia. Electromyography (EMG) showed only scattered fibrillation potentials and short duration motor unit potentials. Muscle biopsy showed nonspecific myopathic features and highly atrophic fibers with nuclear clumps. DM2 should be considered in patients with focal proximal weakness and abnormal EMG without myotonic discharges.

Ribonuclear inclusions and MBNL1 nuclear sequestration do not affect myoblast differentiation but alter gene splicing in myotonic dystrophy type 2

Myotonic dystrophy type 2 (DM2) is an autosomal dominant multisystemic disorder caused by a CCTG expansion in intron 1 of the zinc finger protein 9 gene on chromosome 3. Mutant transcripts are retained in muscle nuclei producing ribonuclear inclusions, which can bind specific RNA-binding proteins leading to a reduction in their activity. The nuclear sequestration of muscleblind-like proteins appears to be involved in splicing defects of genes directly related to the myotonic dystrophy phenotypes. Experimental evidence suggests that ribonuclear inclusions and muscleblind-like protein 1 (MBNL1) sequestration are strongly involved in DM2 pathogenesis. By using fluorescence in situ hybridization in combination with MBNL1-immunofluorescence, we have observed the presence of ribonuclear inclusions and MBNL1 nuclear sequestration at different time points of in vitro myoblast differentiation in each DM2 patient examined. Immunofluorescence and Western blot analysis of several markers of skeletal muscle differentiation reveal that the degree of differentiation of DM2 myoblasts is comparable to that observed in controls. Nevertheless the splicing pattern of the insulin receptor and MBNL1 transcripts, directly related to the DM2 phenotype, appears to be altered in in vitro differentiated DM2 myotubes. Our data seem indicate that the presence of ribonuclear inclusions and MBNL1 nuclear foci are involved in alteration of alternative splicing but do not impair DM2 myogenic differentiation.

A Z-DNA sequence reduces slipped-strand structure formation in the myotonic dystrophy type 2 (CCTG) x (CAGG) repeat

All DNA repeats known to undergo expansion leading to human neurodegenerative disease can form one, or several, alternative conformations, including hairpin, slipped strand, triplex, quadruplex, or unwound DNA structures. These alternative structures may interfere with the normal cellular processes of transcription, DNA repair, replication initiation, or polymerase elongation and thereby contribute to the genetic instability of these repeat tracts. We show that (CCTG) x (CAGG) repeats, in the first intron of the ZNF9 gene associated with myotonic dystrophy type 2, form slipped-strand DNA structures in a length-dependent fashion upon reduplexing. The threshold for structure formation on reduplexing is between 36 and 42 repeats in length. Alternative DNA structures also form in (CCTG)(58) x (CAGG)(58) and larger repeat tracts in plasmids at physiological superhelical densities. This represents an example of a sequence that forms slipped-strand DNA from the energy of DNA supercoiling. Moreover, Z-DNA forms in a (TG) x (CA) tract within the complex repeat sequence 5' of the (CCTG)(n) x (CAGG)(n) repeat in the ZNF9 gene. Upon reduplexing, the presence of the flanking sequence containing the Z-DNA-forming tract reduced the extent of slipped-strand DNA formation by 62% for (CCTG)(57) x (CAGG)(57) compared with 58 pure repeats without the flanking sequence. This finding suggests that the Z-DNA-forming sequence in the DM2 gene locus may have a protective effect of reducing the potential for slipped-strand DNA formation in (CCTG)(n) x (CAGG)(n) repeats.

Myotonic dystrophy type 2 found in two of sixty-three persons diagnosed as having fibromyalgia

Because of its high prevalence, fibromyalgia (FM) is a major general health issue. Myotonic dystrophy type 2 (DM2) is a recently described autosomal-dominant multisystem disorder. Besides variable proximal muscle weakness, myotonia, and precocious cataracts, muscle pain and stiffness are prominent presenting features of DM2. After noting that several of our mutation-positive DM2 patients had a previous diagnosis of FM, suggesting that DM2 may be misdiagnosed as FM, we invited 90 randomly selected patients diagnosed as having FM to undergo genetic testing for DM2. Of the 63 patients who agreed to participate, 2 (3.2%) tested positive for the DM2 mutation. Their cases are described herein. DM2 was not found in any of 200 asymptomatic controls. We therefore suggest that the presence of DM2 should be investigated in a large sample of subjects diagnosed as having FM, and clinicians should be aware of overlap in the clinical presentation of these 2 distinct disorders.

Flowcytometric phenotyping of common variable immunodeficiency

BACKGROUND

Common variable immunodeficiency (CVID) comprises heterogeneous antibody deficiency disorders. To classify this heterogeneous syndrome, clinical as well as immunologic parameters have been combined. Flowcytometric analysis of circulating T and B lymphocyte subpopulations has become an important tool in this endeavor of disease classification.

METHODS

Multicolor flowcytometric analysis of circulating lymphocytes.

RESULTS

The flowcytometric analysis of B and T cell subpopulations in the blood of CVID patients has contributed significantly to the identification of separate groups within the CVID population. In addition, the flowcytometric analysis of the inducible costimulator on activated T cells, CD19 and BAFF-R on B cells are valid screening methods for three of the four known genetic defects associated with CVID. Only TACI deficiency can not be sufficiently detected by flowcytometric measures.

CONCLUSIONS

Flowcytometric classification of patients with CVID has become a standard procedure during the diagnostic work up. This should be performed according to common guidelines to guarantee world wide comparability between different immunodeficiency centers.

High frequency of co-segregating CLCN1 mutations among myotonic dystrophy type 2 patients from Finland and Germany

Based on previous reports the frequency of co-segregating recessive chloride channel (CLCN1) mutations in families with myotonic dystrophy type 2 (DM2) was suspected to be increased. We have studied the frequency of CLCN1 mutations in two separate patient and control cohorts from Germany and Finland, and for comparison in a German myotonic dystrophy type 1 (DM1) patient cohort. The frequency of heterozygous recessive chloride channel (CLCN1) mutations is disproportionally higher (5 %) in currently diagnosed DM2 patients compared to 1.6 % in the control population (p = 0.037), while the frequency in DM1 patients was the same as in the controls. Because the two genes segregate independently, the prevalence of CLCN1 mutations in the total DM2 patient population is, by definition, the same as in the control population. Our findings are, however, not based on the total DM2 population but on the currently diagnosed DM2 patients and indicate a selection bias in molecular diagnostic referrals. DM2 patients with co-segregating CLCN1 mutation have an increased likelihood to be referred for molecular diagnostic testing compared to DM2 patients without co-segregating CLCN1 mutation.

Colocalization of ribonuclear inclusions with muscle blind like-proteins in a family with myotonic dystrophy type 2 associated with a short CCTG expansion

Myotonic dystrophy type 2 (DM2) is an autosomal dominant multisystemic disorder caused by a CCTG repeat expansion in intron 1 of the zinc finger protein 9 (ZNF9) gene. We present a three first-degree relative Italian family (proband, his mother and his sister) with a mild DM2 phenotype associated with a short (CCTG)(100) expansion as far as regards the proband and his mother, while his sister shows larger expansion correlated to a more severe phenotype. FISH analysis with (CAGG)(5) probe demonstrated that nuclear foci of mutant RNA were present in the proband muscle and co-localized with muscleblind-like proteins, determining their sequestration in the nucleus. This is one of the smallest expansion reported and the shortest with the evidence of nuclear foci. These data contribute to the clinical and molecular correlation of ZNF9 gene short expansion.

Muscle diseases: the muscular dystrophies

Dystrophic muscle disease can occur at any age. Early- or childhood-onset muscular dystrophies may be associated with profound loss of muscle function, affecting ambulation, posture, and cardiac and respiratory function. Late-onset muscular dystrophies or myopathies may be mild and associated with slight weakness and an inability to increase muscle mass. The phenotype of muscular dystrophy is an endpoint that arises from a diverse set of genetic pathways. Genes associated with muscular dystrophies encode proteins of the plasma membrane and extracellular matrix, and the sarcomere and Z band, as well as nuclear membrane components. Because muscle has such distinctive structural and regenerative properties, many of the genes implicated in these disorders target pathways unique to muscle or more highly expressed in muscle. This chapter reviews the basic structural properties of muscle and genetic mechanisms that lead to myopathy and muscular dystrophies that affect all age groups.

MBNL1 associates with YB-1 in cytoplasmic stress granules

The muscleblind-like (MBNL) protein family is thought to be involved in the molecular mechanism of myotonic dystrophy (DM). Although it has been shown to have splicing activity, a broader function in cellular RNA metabolism has been implicated. In this study, we attempted to find the binding proteins of MBNL1 in order to elucidate its physiological function. First, we performed a GST pull-down assay using GST-MBNL1-6xHis as bait. Several proteins were identified, including YB-1, a multifunctional DNA/RNA-binding protein, and DDX1, a DEAD box RNA helicase. MBNL1 formed an RNP complex with YB-1 and DDX1 in binding assays. YB-1 also showed a weak but significant effect on alpha-actinin splice site selection. Interestingly, in response to stress, MBNL1 moved to cytoplasmic stress granules, where it colocalized with YB-1, which was previously reported to be a component of stress granules. We found that DDX1 also colocalized with MBNL1 at stress granules. These results provide new insight into the dynamics of MBNL1 in response to stress, and they suggest a role for MBNL1 in mRNA metabolism in the cytoplasm.

Primary myopathies and the heart

Myopathies are frequently not confined to the skeletal muscles but also involve other organs or tissues. One of the most frequently affected organ in addition to the skeletal muscle is the heart (cardiac involvement, CI). CI manifests as impulse generation or conduction defects, focal or diffuse myocardial thickening, dilation of the cardiac cavities, relaxation abnormality, hypertrophic, dilated, restrictive cardiomyopathy, apical form of hypertrophic cardiomyopathy, noncompaction, Takotsubo phenomenon, secondary valve insufficiency, intra-cardiac thrombus formation, or heart failure with systolic or diastolic dysfunction. CI occurs in dystrophinopathies, Emery-Dreifuss muscular dystrophy, facioscapulohumeral muscular dystrophy, limb girdle muscular dystrophies, laminopathies, congenital muscular dystrophies, myotonic dystrophies, congenital myopathies, metabolic myopathies, desminopathies, myofibrillar myopathy, Barth syndrome, McLeod syndrome, Senger's syndrome, and Bethlem myopathy. Patients with myopathy should be cardiologically investigated as soon as their neurological diagnosis is established, since supportive cardiac therapy is available, which markedly influences prognosis and outcome of CI in these patients.

Myotonic dystrophy type I in childhood Long-term evolution in patients surviving the neonatal period

In a retrospective study, 32 patients with myotonic dystrophy, including congenital (n=17) and infantile/juvenile forms (n=15) were studied during a long follow-up lasting 7-28 years (median: 17 years). The clinical presentation was extremely variable; however, a continuum did exist between severe and less severe congenital forms, and later-onset forms, without genotype-phenotype correlation. We observed some unusual presentations, such as 3 cases of isolated club-feet during the neonatal period, and 7 patients (23%) with a completely isolated mental deficiency, language delay and school failure, who only completed the clinical picture several years later. Wechsler scale testing was performed in all cases, and repeated with 8 patients. It demonstrated a decrease in intellectual abilities in 5 patients, suggesting the possibility of a degenerative cerebral process occurring in these children. This decrease has also been reported in some adult cases. This study illustrates the extremely heterogeneous clinical presentation of myotonic dystrophy in childhood.

[Ocular disturbances in neuromuscular disorders]

Compared with other skeletal muscles, extraocular muscles have fundamentally distinct properties that make them selectively vulnerable to certain neuromuscular disorders. When the oculomotor signs are predominant, their temporal progression allows the clinician to make the distinction between a muscular disease (mitochondrial disorder, oculopharyngeal muscular dystrophy...) and a disorder of the neuromuscular junction (myasthenia gravis, botulism...). In other instances, such as myotonic dystrophy or facioscapulohumeral dystrophy, the ocular signs are not in the forefront but must be recognized by the ophthalmologist as hallmarks of a muscular disorder. In all cases, the collaboration between the neurologist and the ophthalmologist is fruitful.

Defining early steps in mRNA transport: mutant mRNA in myotonic dystrophy type I is blocked at entry into SC-35 domains

In myotonic dystrophy type 1 (DM1), triplet repeat expansion in the 3' untranslated region of dystrophia myotonica protein kinase (DMPK) causes the nuclear retention of mutant messenger RNA (mRNA). Although the DMPK gene locus positions precisely at the outer edge of a factor-rich SC-35 domain, the normal mRNA consistently accumulates within the domain, and this RNA is depleted upon transcriptional inhibition. In DM1, mutant transcripts detach from the gene but accumulate in granules that abut but do not enter SC-35 domains, suggesting that RNA entry into the domain is blocked. Despite their exclusion from these compartments, mutant transcripts are spliced. MBNL1 (muscleblind-like protein 1) is an alternative splicing factor that becomes highly concentrated with mutant RNA foci. Small interfering RNA-mediated knockdown of MBNL1 promotes the accumulation or entry of newly synthesized mutant transcripts in the SC-35 domain. Collectively, these data suggest that an initial step in the intranuclear path of some mRNAs is passage from the gene into an SC-35 domain and implicate these structures in postsplicing steps before export.

Severity, type, and distribution of myotonic discharges are different in type 1 and type 2 myotonic dystrophy

To characterize and compare electrical myotonia in myotonic dystrophy type 1 (DM1) and type 2 (DM2), 16 patients with genetically confirmed DM1 and 17 patients with DM2 underwent standardized concentric needle electromyography of deltoid, biceps, extensor digitorum communis, first dorsal interosseous, tensor fascia lata (TFL), vastus lateralis (VL), tibialis anterior, and thoracic paraspinal muscles. Eight needle insertions per muscle were made by electromyographers blinded to DM type who recorded the presence and type of myotonia (e.g., classic waxing-waning or less specific waning discharges). Manual muscle testing was performed by a physical therapist. Overall, myotonia was more elicitable in DM1 than DM2; only in VL and TFL was myotonia more elicitable in DM2 than DM1. The major type of myotonia was waxing-waning in DM1, and waning in DM2. Four DM2 (24%), but no DM1 patients had only waning myotonia. In the arms, myotonia was distally predominant in both DM1 and DM2. In the legs, it was distally predominant in DM1, but both proximal and distal in DM2. The severity of myotonia was positively correlated with muscle weakness and with the presence of waxing and waning discharges in DM1, but with neither in DM2. Thus, myotonia is qualitatively and quantitatively different in DM1 than DM2. Except for proximal leg muscles, myotonia is more evocable in DM1 than DM2. It tends to be waxing-waning in DM1 but waning in DM2, thus making electrodiagnosis of DM2 more challenging. Its severity correlates with muscle weakness and the presence of waxing-waning discharges in DM1 but not DM2.

Haploinsuffciency for Znf9 in Znf9+/− Mice Is Associated with Multiorgan Abnormalities Resembling Myotonic Dystrophy

Myotonic dystrophy type 2 is caused by a (CCTG)/(CCUG)n repeat expansion in the first intron of the ZNF9 gene. The pathomechanism for the myotonic dystrophies is not well understood and the role of ZNF9 in myotonic dystrophy type 2 pathogenesis has not been fully clarified. We characterized Znf9+/- mice, in which the expression of Znf9 was significantly decreased, and found that their phenotype reflects many of the features of myotonic dystrophy, including muscle histological morphology, and myotonic discharges and heart conduction abnormalities, shown by electromyography and electrocardiogram analysis, respectively. Znf9 is normally highly expressed in heart and skeletal muscle, where skeletal muscle chloride channel 1 (Clc1) plays an important role. Clc1 expression was dramatically decreased in Znf9+/- mice. Znf9 transgenic mice raised Znf9 and Clc1 expression and rescued the myotonic dystrophy phenotype in Znf9+/- mice. Our results suggest that the Znf9 haploinsufficiency contributes to the myotonic dystrophy phenotype in Znf9+/- mice.

Myotonic dystrophy: Emerging mechanisms for DM1 and DM2

Myotonic dystrophy (DM) is a complex multisystemic disorder linked to two different genetic loci. Myotonic dystrophy type 1 (DM1) is caused by an expansion of a CTG repeat located in the 3' untranslated region (UTR) of DMPK (myotonic dystrophy protein kinase) on chromosome 19q13.3. Myotonic dystrophy type 2 (DM2) is caused by an unstable CCTG repeat in intron 1 of ZNF9 (zinc finger protein 9) on chromosome 3q21. Therefore, both DM1 and DM2 are caused by a repeat expansion in a region transcribed into RNA but not translated into protein. The discovery that these two distinct mutations cause largely similar clinical syndromes put emphasis on the molecular properties they have in common, namely, RNA transcripts containing expanded, non-translated repeats. The mutant RNA transcripts of DM1 and DM2 aberrantly affect the splicing of the same target RNAs, such as chloride channel 1 (ClC-1) and insulin receptor (INSR), resulting in their shared myotonia and insulin resistance. Whether the entire disease pathology of DM1 and DM2 is caused by interference in RNA processing remains to be seen. This review focuses on the molecular significance of the similarities and differences between DM1 and DM2 in understanding the disease pathology of myotonic dystrophy.

Length-dependent toxicity of untranslated CUG repeats on Caenorhabditis elegans

Expansion of CTG repeat within the 3'-untranslated region of the DMPK gene causes the most common neuromuscular disorder, myotonic dystrophy type 1 (DM1), through a RNA trans-dominant mechanism. Here, we explore Caenorhabditis elegans as a model system to investigate the repeat size-dependent toxic effect by expression of green fluorescent protein (GFP) transcripts with various lengths of untranslatable CUG repeats (CUG5, CUG30, CUG83, CUG125, and CUG213) in body wall muscles. CUG213 animals died during embryogenesis or showed retarded growth at larval stages due to defective muscle development. CUG125 animals, although can produce offspring, exhibited uncoordinated muscle function, deviated electropharyngeogram, and an age-dependent abnormality in muscle structure. Most CUG83 animals had normal muscle structure and function as those expressing 30 and shorter repeats. Our results demonstrate for the first time that the in vivo toxicity of CUG repeats is repeat length- and growth-regulated and suggest that expanded CUG repeats are sufficient to cause congenital-like phenotypes in living organisms.

Unusual clinical, laboratory, and muscle histopathological findings in a family with myotonic dystrophy type 2

Myotonic dystrophy type 2 (DM2) is a multisystem degenerative disorder with distinctive clinical and electrophysiological features. Recently, genetic confirmation has become available with the identification of the molecular defect, an expansion of a CCTG repeat located in intron 1 of the zinc finger protein 9 (ZNF9) gene. We present two first-degree relatives with an athletic clinical phenotype, pathological evidence of subsarcolemmal vacuolation, and molecular genetic confirmation of DM2. When found in the proper clinical context, athleticism and pathological subsarcolemmal vacuoles should not dissuade the clinician from the possible diagnosis of DM2.

RNA-MEDIATED NEUROMUSCULAR DISORDERS

Myotonic dystrophy type 1 (DM1) is caused by a CTG expansion mutation located in the 3' untranslated portion of the dystrophica myotonin protein kinase gene. The identification and characterization of RNA-binding proteins that interact with expanded CUG repeats and the discovery that a similar transcribed but untranslated CCTG expansion in an intron causes myotonic dystrophy type 2 (DM2) have uncovered a new type of mechanism in which microsatellite expansion mutations cause disease through an RNA gain-of-function mechanism. This review discusses RNA pathogenesis in DM1 and DM2 and evidence that similar mechanisms may play a role in a growing number of dominant noncoding expansion disorders, including fragile X tremor ataxia syndrome (FXTAS), spinocerebellar ataxia type 8 (SCA8), SCA10, SCA12, and Huntington's disease-like 2 (HDL2).

Large pathogenic expansions in the SCA2 and SCA7 genes can be detected by fluorescent repeat-primed polymerase chain reaction assay

Large expansions in the SCA2 and SCA7 genes (>100 CAG repeats) have been associated with juvenile and infantile forms of cerebellar ataxias that cannot be detected using standard polymerase chain reaction (PCR). Here, we describe a successful application of the fluorescent short tandem repeat-primed PCR method for accurate identification of these expanded repeats. The test is robust, reliable, and inexpensive and can be used to screen large series of patients, although it cannot give a precise evaluation of the size of the expansion. This test may be of practical value in prenatal diagnoses offered to affected or pre-symptomatic at-risk parents, in which a very large expansion inherited from one of the parents can be missed in the fetus by standard PCR.

Myotonic dystrophies type 1 and 2: a summary on current aspects

Myotonic dystrophies (DMs) encompass at least 2 forms: myotonic dystrophy type 1 and 2. In general, DMs are late-onset autosomal dominant disorders characterized by a variety of multisystemic features including myotonia, muscular dystrophy, cardiac conduction defects, dilated cardiomyopathy, posterior iridescent cataracts, frontal balding, insulin-resistance and disease-specific serological abnormalities such as gamma-glutamyltransferase and creatine kinase elevations, hyperglycemia, hypotestosteronism, and reduced immunoglobulin (Ig) G and IgM levels. Beyond the adult forms, in the classic DM1, a congenital form and an early-onset form is recognized. Here we summarize current aspects of the myotonic dystrophy pathogenesis and review the core features of both types of myotonic dystrophies, including the congenital DM1.

DM2 intronic expansions: evidence for CCUG accumulation without flanking sequence or effects on ZNF9 mRNA processing or protein expression

Myotonic dystrophy type 2 (DM2) is caused by a CCTG expansion mutation in intron 1 of the zinc finger protein 9 (ZNF9) gene. The mean expansion size in patients is larger than for DM1 or any previously reported disorder (mean=5000 CCTGs; range=75-11 000), and similar to DM1, repeats containing ribonuclear inclusions accumulate in affected DM2 tissue. Although an RNA gain-of-function mechanism involving DM1 CUG or DM2 CCUG expansion transcripts is now well established, still debated are the potential role that flanking sequences within the DMPK 3'-UTR may have on disease pathogenesis and whether or not decreased expression of DMPK, ZNF9 or neighboring genes at these loci contribute to disease. To address these questions in DM2, we have examined the nucleic acid content of the ribonuclear inclusions and the effects of these large expansions on ZNF9 expression. Using cell lines either haploid or homozygous for the expansion, as well as skeletal muscle biopsy tissue, we demonstrate that pre-mRNAs containing large CCUG expansions are normally spliced and exported from the nucleus, that the expansions do not decrease ZNF9 expression at the mRNA or protein level, and that the ribonuclear inclusions are enriched for the CCUG expansion, but not intronic flanking sequences. These data suggest that the downstream molecular effects of the DM2 mutation are triggered by the accumulation of CCUG repeat tract alone.

Distinct neuromuscular phenotypes in myotonic dystrophy types 1 and 2 : a whole body highfield MRI study

Myotonic Dystrophy Type 1 (DM1) and 2 (DM2) present with distinct though overlapping clinical phenotypes. Comparative imaging data on skeletal muscle involvement are not at present available. We used the novel technique of whole body 3.0 Tesla (T) Magnetic Resonance Imaging (MRI) to further characterize musculoskeletal features in DM2 and compared the results with DM1.MRI findings of 15 DM1 and 14 DM2 patients were evaluated with respect to patterns of skeletal muscle affection and clinical data using the Muscular Impairment Rating Scale (MIRS) and Medical Research Council scale (MRC). All DM1 patients had pathological MRI compared with only 5 DM2 patients. In contrast to DM2, DM1 patients showed a characteristic distribution of muscle involvement with frequent and early degeneration of the medial heads of gastrocnemius muscles, and a perifemoral semilunar pattern of quadriceps muscle affection sparing the rectus femoris. The most frequently affected muscles in DM1 were the medial heads of gastrocnemius, soleus, and vastus medialis muscles. In DM2, however, the erector spinae and gluteus maximus muscles were most vulnerable to degeneration. MRI data were in line with the clinical grading in 12 DM1 and 3 DM2 patients. In 3 DM1 and 5 DM2 patients, MRI detected subclinical muscle involvement. 9 DM2 patients with mild to moderate proximal muscle weakness and/or myalgias had normal MRI. Pathological MRI changes in DM2 emerged with increasing age and were restricted to women. Whole body 3.0T MRI is a sensitive imaging technique that demonstrated a characteristic skeletal muscle affection in DM1. In contrast, MRI was no reliable indicator for skeletal muscle involvement in mildly affected DM2 patients since myalgia and mild paresis were usually not reflected by MRI signal alterations.

Chemical modifiers of unstable expanded simple sequence repeats: what goes up, could come down

A mounting number of inherited human disorders, including Huntington disease, myotonic dystrophy, fragile X syndrome, Friedreich ataxia and several spinocerebellar ataxias, have been associated with the expansion of unstable simple sequence DNA repeats. Despite a similar genetic basis, pathogenesis in these disorders is mediated by a variety of both loss and gain of function pathways. Thus, therapies targeted at downstream pathology are likely to be disease specific. Characteristically, disease-associated expanded alleles in these disorders are highly unstable in the germline and somatic cells, with a tendency towards further expansion. Whereas germline expansion accounts for the phenomenon of anticipation, tissue-specific, age-dependent somatic expansion may contribute towards the tissue-specificity and progressive nature of the symptoms. Thus, somatic expansion presents as a novel therapeutic target in these disorders. Suppression of somatic expansion should be therapeutically beneficial, whilst reductions in repeat length could be curative. It is well established that both cis- and trans-acting genetic modifiers play key roles in the control of repeat dynamics. Importantly, recent data have revealed that expanded CAG.CTG repeats are also sensitive to a variety of trans-acting chemical modifiers. These data provide an exciting proof of principle that drug induced suppression of somatic expansion might indeed be feasible. Moreover, as our understanding of the mechanism of expansion is refined more rational approaches to chemical intervention in the expansion pathway can be envisioned. For instance, the demonstration that expansion of CAG.CTG repeats is dependent on the Msh2, Msh3 and Pms2 genes, highlights components of the DNA mismatch repair pathway as therapeutic targets. In addition to potential therapeutic applications, the response of expanded simple repeats to genotoxic assault suggests such sequences could also have utility as bio-monitors of environmentally induced genetic damage in the soma.

Neuromuscular disorders in pregnancy

Many neuromuscular conditions occur more frequently during pregnancy and include carpal tunnel syndrome, Bell's palsy, lumbosacral radiculopathy, meralgia paresthetica, intercostal neuralgia, and other compression neuropathies. Preexisting or coincident neuromuscular diseases, including demyelinating polyneuropathies, inflammatory muscle disease, myasthenia gravis, and inherited nerve and muscle disease present specific problems during pregnancy. We review management of neuromuscular disorders during pregnancy, labor, delivery, and the early postpartum period.

Female patient with proximal myotonic myopathy and ventricular tachycardia

A 68-year-old woman with known proximal myotonic myopathy was transferred to our hospital for further diagnostic and therapeutic evaluation after successful termination of an episode of sustained ventricular tachycardia. In 2001, the myopathy was diagnosed after symptomatic weakness of the hip flexors. A cardiomyopathy with slight reduction of systolic left ventricular function was found in 2002. Coronary angiography excluded relevant coronary artery disease. The electrophysiologic examination could provoke atrial flutter, but neither a ventricular tachycardia nor a delay in the AV conduction was found. ECG and Holter ECG did not reveal any abnormalities. A reduction of the left ventricular systolic function (EF 45%) with normal size of cardiac chambers was demonstrated by echocardiography. It is known that in the patient group with myotonic dystrophies cardiac involvement manifests itself as cardiomyopathy, conduction disturbance or arrhythmia. However, only a small percentage of all patients with myotonic myopathy actually suffer from cardiac involvement. Among the different types of cardiac involvement, conduction disturbances requiring pacemaker implantation are most frequent. Only some patients develop ventricular tachycardias, and even cases of sudden cardiac death have been described. As a result of the case reports in the literature and the findings in our patient an ICD system was implanted on March 4, 2004.

Common variable immunodeficiency: test indications and interpretations

Common variable immunodeficiency (CVID) is a primary immunodeficiency disorder that can present with multiple phenotypes, all of which are characterized by hypogammaglobulinemia, in a person at any age. A specific genetic defect that accounts for all CVID phenotypes has not been identified, and it is likely that several distinct genetic disorders with similar clinical presentations are responsible for the observed variation. In this review, we summarize the known genetic mutations that give rise to hypogammaglobulinemia and how these gene products affect normal or abnormal B-cell development and function, with particular emphasis on CVID. Additionally, we describe specific phenotypic and genetic laboratory tests that can be used to diagnose CVID and provide guidelines for test interpretation and subsequent therapeutic intervention.

Clinical and molecular aspects of the myotonic dystrophies: a review

Type 1 myotonic dystrophy or DM1 (Steinert's disease), which is the commonest muscular dystrophy in adults, has intrigued physicians for over a century. Unusual features, compared with other dystrophies, include myotonia, anticipation, and involvement of other organs, notably the brain, eyes, smooth muscle, cardiac conduction apparatus, and endocrine system. Morbidity is high, with a substantial mortality relating to cardiorespiratory dysfunction. More recently a second form of multisystem myotonic disorder has been recognized and variously designated as proximal myotonic myopathy (PROMM), proximal myotonic dystrophy (PDM), or DM2. For both DM1 and DM2 the molecular basis is expansion of an unstable repeat sequence in a noncoding part of a gene (DMPK in DM1 and ZNF9 in DM2). There is accumulating evidence that the basic molecular mechanism is disruption of mRNA metabolism, which has far-reaching effects on many other genes, in part through the induction of aberrant splicing, explaining the multisystemic nature of the disease. The unstable nature of the expansion provides a molecular explanation for anticipation. This review emphasizes the clinical similarities and differences between DM1 and DM2. It examines current views about the molecular basis of these disorders, and contrasts them with other repeat expansion disorders that have increasingly been recognized as a cause of neurological disease.

Hyper-CK-emia as the sole manifestation of myotonic dystrophy type 2

A 49-year-old man had an 8-year history of persistent, isolated elevation of serum creatine kinase (hyper-CK-emia) without muscle symptoms, and no electromyographic evidence of myotonia; his muscle biopsy showed features reminiscent of myotonic dystrophy (DM), with morphometric findings consistent with those described in DM type 2 (DM2). Genetic studies excluded mutations in the DM type 1 (DM1) gene, but revealed a CCTG repeat expansion in the ZNF9 gene, which is associated with DM2. Our data suggest that in asymptomatic patients with persistent hyper-CK-emia, DM2 should be considered in the differential diagnosis.

Common neonatal syndromes

The process of diagnosis of genetic syndromes in the newborn period is carried out in the context of parental anxiety and the grief following an often-unexpected outcome after a long pregnancy. The nursery staffs invariably have a strong interest in giving the family proper information about prognosis. This article is intended to focus on an approach to the diagnosis of genetic syndromes and to discuss specific syndromes that may be seen with some frequency in the nursery.