Dystonia 11, Myoclonic

A number sign (#) is used with this entry because of evidence that myoclonic dystonia-11 (DYT11) is caused by heterozygous mutation in the epsilon-sarcoglycan gene (SGCE; 604149) on chromosome 7q21.

Description

Myoclonus-dystonia is a genetically heterogeneous disorder characterized by myoclonic jerks affecting mostly proximal muscles. Dystonia, usually torticollis or writer's cramp, is observed in most patients, but occasionally can be the only symptom of the disorder. Onset of the disorder is usually in the first or second decade. Symptoms often respond to alcohol, and patients may also have psychiatric abnormalities (Valente et al., 2003; Schule et al., 2004).

Clinical Features

Myoclonic dystonia, or myoclonus-dystonia, has dystonia as the core feature, but tremor or rapid jerky movements resembling myoclonus may also be present. The age of onset, pattern of body involvement, presence of myoclonus, and response to alcohol are all variable. Essential myoclonus is a relatively mild condition starting in the first or second decade, and is inherited as an autosomal dominant trait with incomplete penetrance. Some patients with essential myoclonus also have dystonia, but there are usually no other neurologic symptoms, and there may be a dramatic response to alcohol (Nemeth, 2002).

In a family of French Canadian background, a father and 5 of his 9 children showed onset of myoclonus in the first or second decade and a benign course without seizures, dementia, or neurologic signs other than myoclonus (Mahloudji and Pikielny, 1967). Because of the uncertainty of the nature of the case, on the basis of which Friedreich in 1881 introduced the term paramyoclonus multiplex, these cases might best be called hereditary essential myoclonus.

Daube and Peters (1966) reported 2 families with hereditary essential myoclonus in each of which affected members occurred in at least 4 generations, with male-to-male transmission but some skipped generations. Symonds (1953) described nocturnal myoclonus in a man and 5 of his 6 children. Muller and Kupke (1990) interpreted the family reported by Mahloudji and Pikielny (1967) as an instance of what they termed myoclonic dystonia, i.e., the association of torsion dystonia with myoclonus (muscle jerks). They pointed to families with the same disorder reported by Benedek and Rakonitz (1940), Quinn et al. (1988), and Kurlan et al. (1988).

Unlike other forms of dystonia (e.g., 128100), myoclonic dystonia may be highly responsive to ethanol ingestion and frequently also to clonazepam therapy and usually pursues a benign course. Kyllerman et al. (1990) described a 6-generation Swedish family with alcohol-responsive hereditary myoclonus. After clinical examination of 20 affected persons, myoclonus was found in the arms, shoulders, and neck of 17. The onset of myoclonus was between 2 and 3 years of age. The onset of leg dystonia was from 6 to 18 months of age.

Nygaard et al. (1999) reported a large American kindred of European and Native American ancestry with essential familial myoclonic dystonia that was responsive to alcohol. There were 10 definitely affected living individuals. Four had both myoclonus and dystonia, 5 had myoclonus alone, and 1 had brachial dystonia only. However, among the 5 judged to have only myoclonus, 4 had occasional sustained contractions and subtle posturing that might suggest mild dystonia. Mean age at onset of symptoms was 6.5 years (range, 4 to 15 years) in the 8 individuals able to recall onset. All affected individuals who tried alcohol reported relief of symptoms. Several family members had sought medical attention; levodopa was ineffective, and clonazepam or valproate gave mild benefit. Nine out of the 10 affected family members reported psychiatric problems, including diagnoses and treatment for depression, anxiety, and obsessive-compulsive disorder.

Asmus et al. (2002) reported 24 affected patients from 9 families, confirmed by genetic analysis of the SGCE gene (1 previously known and 6 novel heterozygous mutations were identified). The clinical presentation was homogeneous, with myoclonus affecting primarily the neck, trunk, and upper extremities at a mean age of onset of 5.4 years (range 0.5 to 20 years). Dystonia presented mostly in a focal distribution as cervical dystonia and/or writer's cramp at a mean age of onset of 8.8 years (range 1 to 38 years), often occurring in parallel with worsening of myoclonus. Myoclonus was improved by alcohol in 21 of 24 affected, and 5 affected members of 3 families had a history of panic attacks, depression, and agoraphobia. Pedigree analysis showed reduced penetrance of the phenotype upon maternal inheritance of the mutated allele, indicating genomic imprinting.

Doheny et al. (2002) described in detail the motor symptoms, psychiatric disorders, and neuropsychologic deficits in 3 families with myoclonus-dystonia syndrome who carried mutations in the SGCE gene. One family also carried a mutation in the DRD2 gene. Motor expression was variable, with onset of myoclonus or dystonia or both affecting the upper body and progression to myoclonus and dystonia in most cases. Psychiatric profiles revealed depression, obsessive-compulsive disorder, substance abuse, anxiety/panic/phobic disorders, and psychosis in 2 families, and depression only in the third family. Averaged scores from cognitive testing showed impaired verbal learning and memory in 1 family, impaired memory in the second family, and no cognitive deficits in the third family. Doheny et al. (2002) concluded that cognitive deficits may be associated with myoclonus-dystonia and that psychiatric abnormalities correlated with motor symptoms in affected individuals.

In a large family with myoclonus-dystonia syndrome and a mutation in the SGCE gene (604149.0008), Hjermind et al. (2003) reported prominent involvement of the legs, leading to disability in some, and laryngeal involvement causing vocal myoclonus.

Valente et al. (2005) identified SGCE mutations in 6 (21%) of 29 patients with essential myoclonus and myoclonic dystonia; no SGCE mutations were identified in another 29 patients with a broader myoclonus/dystonia phenotype. The patients with mutations typically had early onset of predominant myoclonus and milder dystonia, with an upper body predilection. Dystonia tended to have a later onset than that of myoclonus. Most patients' symptoms improved with alcohol. Autosomal dominant paternal inheritance was observed. Valente et al. (2005) noted the clinical phenotypic overlap of myoclonic dystonia, essential myoclonus, 'jerky' dystonia, Ramsay Hunt syndrome (159700), and benign hereditary chorea (118700).

Gerrits et al. (2006) reported 31 unrelated patients with a clinical diagnosis of myoclonus-dystonia, of whom 7 were found to have mutations in the SGCE gene. Clinical comparisons between mutation-positive and mutation-negative patients showed that the former had earlier disease onset before age 20 years. Mutation carriers first presented mostly with both myoclonus and dystonia, whereas mutation-negative patients usually presented with 1 or the other symptom. Those with mutations also tended to have a family history of the disorder, as well as truncal myoclonus and axial dystonia. There were no significant differences between the 2 groups regarding alcohol sensitivity or psychiatric symptoms.

Roze et al. (2008) reviewed the features of 41 patients from 22 French families with SGCE mutation-positive myoclonus dystonia. The mean age at onset was 6 years (range, 1 to 18 years). Myoclonus was the presenting feature in 29 patients, 5 of whom also presented with dystonia. Ten patients presented with isolated dystonia, and 2 patients from the same family presented with hypotonia. Dystonia was axial, mostly cervical, in 13 patients, in the upper limbs in 18 patients, and in the lower limbs in 9 patients. One patient had laryngeal dystonia. Myoclonus involved the axis in 90% of cases, most commonly with cervical and upper limb involvement. Myoclonus of the face and voice occurred in 27% and 24%, respectively, and involved the lower limbs in 34% of patients. Myoclonus was present at rest in 70% of patients, and increased with posture and action in 95%. Neurophysiologic studies showed that myoclonus could be synchronous or asynchronous, isolated, and mostly arrhythmic. The studies indicated a subcortical origin: myoclonus was stimulus insensitive; the mean duration of myoclonus was 95 seconds, which is longer than that observed in cortical myoclonus; and there were no features of cortical hyperexcitability, as reflected by a negative C-reflex response. Nine patients had spontaneous remission of the dystonia during childhood or adolescence. Eight patients had associated psychiatric disturbances, including obsessive-compulsive disorder, severe anxiety and depression, attention-deficit hyperactivity disorder, and phobic disorder. There were no clear genotype/phenotype correlations.

Other Features

Hess et al. (2007) studied psychiatric manifestations in 5 unrelated families with myoclonus-dystonia confirmed by genetic analysis. Among a total of 64 family members, manifesting SGCE mutation carriers showed increased alcohol dependence compared to nonmanifesting carriers and controls (35% and 11.4%, respectively), but the association was not significant for the mutation carrier group overall. There was an increase in the rate of obsessive-compulsive disorder (OCD) in mutation carriers compared to non-carriers (16.7% and 3.0%, respectively), but it did not reach significance. However, there was no case of OCD among 10 nonmanifesting carriers, and only 1 noncarrier fit OCD criteria. In patients with OCD, the onset of motor symptoms preceded OCD by about 10 years. Hess et al. (2007) concluded that alcohol dependence in myoclonus-dystonia patients is related to self-medication to improve motor symptoms, whereas OCD may be a manifestation of mutant gene expression triggered after the onset of movement symptoms.

Clinical Management

Azoulay-Zyss et al. (2011) reported favorable results in 5 patients with severe and refractory myoclonus-dystonia treated with bilateral deep brain stimulation of the internal pallidum. All patients showed significant functional improvement and improvement on measurable scoring systems at 6 to 9 months after surgery. The median improvement in score was an 85% decrease for dystonia and an 83% decrease for myoclonus. After 15 to 18 months, 3 patients were medication-free, 1 of whom received botulism injections for mild cervical dystonia. The other 2 patients were on low doses of benzodiazepines. There were no adverse effects.

Contarino et al. (2011) reported a significantly favorable motor response in 5 patients with myoclonus-dystonia after deep brain stimulation of the internal pallidum. However, 4 of 5 patients had worsening of preexisting psychiatric disorders after the treatment despite the improvement of the motor disabilities. One patient had no change in the psychiatric comorbidity. Preoperative psychiatric symptoms were present in all 5 patients, and mainly included depressive episodes and social anxiety disorder, but were untreated and not considered severe enough to contraindicate surgery. Contarino et al. (2011) concluded that psychiatric comorbidity may be intrinsic to the disorder or secondary to the movement disorder, but that worsening could not be definitively linked to the treatment. They recommended that pre- and postoperative psychiatric evaluation needs to be considered in all patients with this disorder. Grabli et al. (2011) noted that of the 5 patients in their study (Azoulay-Zyss et al., 2011), all had mild generalized anxiety and 1 had a major depressive episode before the treatment. No clinically meaningful psychiatric adverse effect was identified during 18-month follow-up of these patients, and some patients reported improvement in their anxiety. The discrepancy in the outcome between the 2 studies could not be explained.

Mapping

In the Swedish family reported by Kyllerman et al. (1990), Wahlstrom et al. (1994) excluded linkage of the gene responsible for this disorder to 9q32-q34, where the DYT1 gene (TOR1A; 605204) for susceptibility to early-onset torsion dystonia (128100) was mapped, suggesting another locus was responsible. In a large German kindred with alcohol-responsive myoclonic dystonia, Gasser et al. (1996) also excluded linkage to the 9q34 region.

Linkage to Chromosome 7q21

Zimprich et al. (2001) performed pedigree analysis on all families with myoclonus-dystonia syndrome who had known mutations in SGCE (604149) and/or linkage to chromosome 7q21 (DYT11). The high level of dependence of penetrance on the parental origin of the disease allele was demonstrated. Of 62 clinically affected individuals (40 males and 22 females), 49 inherited the disease from their father and only 4 from their mother. In 9 cases, parental origin could not be determined. In contrast, they found a maternal origin of the affected allele in 14 of 18 clinically asymptomatic carriers (12 males and 6 females, carrier status being determined either by sequencing or by pedigree position), whereas paternal transmission occurred in only 3. In one case, parental origin could not be determined.

Nygaard et al. (1999) mapped the locus for myoclonic dystonia in the large American kindred of European and Native American ancestry studied by them to a 28-cM interval spanning the markers D7S802 and D7S1799 in 7q21-q31. The highest pairwise lod score was 3.91 at theta of 0.0 at both D7S657 and D7S796.

Klein et al. (2000) performed genetic studies in 8 families with myoclonic dystonia. In all 8 families, they found linkage to chromosome 7 markers, with a combined multipoint lod score of 11.71. Recombination events in the families placed the disease gene within a 14-cM interval flanked by D7S2212 and D7S821. These data provided evidence for a major locus for myoclonic dystonia on 7q21.

Asmus et al. (2001) narrowed the 7q21-q31 locus for the myoclonus-dystonia syndrome in German families.

Vidailhet et al. (2001) performed linkage analysis in 3 families with myoclonic dystonia and 1 family with essential myoclonus, and found positive lod scores for 6 markers on 7q21-q31 in all families. Linkage to the DRD2 locus was excluded in all families. Although there was wide clinical variation both between and within families in age of onset, involvement of limbs, trunk, or neck, and responsiveness to alcohol, the authors suggested that different phenotypes may be due to allelic mutations in a single gene.

Heterogeneity

Valente et al. (2003) excluded mutations in the SGCE gene in 16 patients with myoclonus dystonia, indicating genetic heterogeneity. Three patients had a family history consistent with autosomal dominant inheritance. Schule et al. (2004) also excluded SGCE mutation in 5 of 7 families with autosomal dominant myoclonus dystonia, again indicating genetic heterogeneity.

Orth et al. (2007) reported a 3-generation family with both myoclonus dystonia and Gilles de la Tourette syndrome (GTS; 137580). There were 11 affected individuals: 3 had myoclonus dystonia, 2 had dystonia, 1 had GTS, 1 had tics, and 4 had various combinations of these with obsessive compulsive disorder. The phenotype of those with myoclonus dystonia was similar to that described for most families, with predominantly head, neck and arm myoclonus, mild cervical dystonia, and writer's cramp. Linkage analysis excluded association to the SGCE, DYT15 (607488), DYT1, or DRD2 (126450) loci, and no pathogenic changes were identified in the SLITRK1 gene (609678). Orth et al. (2007) suggested that there may be a novel susceptibility gene for both myoclonus dystonia and Tourette syndrome.

Molecular Genetics

Using a positional cloning approach, Zimprich et al. (2001) identified 5 different heterozygous loss-of-function mutations in the SGCE (604149.0001-604149.0005) in patients with myoclonus-dystonia syndrome. SGCE was found to be expressed in all brain regions examined. Pedigree analysis showed a marked difference in penetrance depending on the parental origin of the disease allele. This was indicative of a maternal imprinting mechanism, which had been demonstrated in the case of the mouse epsilon-sarcoglycan gene.

Using bisulfite genomic sequencing to study methylation patterns of the SGCE gene in samples from patients with myoclonus-dystonia syndrome, Grabowski et al. (2003) found strong evidence for maternal imprinting of the SGCE gene.

In a Dutch family with myoclonus-dystonia syndrome spanning 5 generations, previously reported by Doheny et al. (2002), Foncke et al. (2003) identified a mutation in the SGCE gene (604149.0007). In addition to the typical motor symptoms, 3 of 5 living affected members also had EEG abnormalities and seizures. Seizures consisted of episodes of reduced consciousness and staring, amnesia, and panic-like feelings, suggestive of temporal-limbic origin. Foncke et al. (2003) suggested that epilepsy should not be considered an exclusion criterion for the clinical diagnosis of myoclonus-dystonia syndrome.

Asmus et al. (2005) identified 2 different large heterozygous deletions in the SGCE gene (604149.0010 and 604149.0011) in affected members from 2 unrelated families with myoclonic dystonia. The deletion was paternally inherited in all cases with motor symptoms. In 1 family, a man who inherited the mutation maternally did not have motor symptoms but did have alcohol dependence.

Tezenas du Montcel et al. (2006) identified 13 different mutations in the SGCE gene in 16 of 76 unrelated French Caucasian patients with myoclonus-dystonia or essential myoclonus. In 12 families (75%), at least 1 other family member was affected. Penetrance was complete in paternal transmissions and null in maternal transmissions. None of the patients had severe psychiatric disorders.

In affected members of a large Dutch family with myoclonus-dystonia syndrome reported by Korten et al. (1974), Foncke et al. (2006) identified a heterozygous mutation in the SGCE gene (604149.0012). The mutation was identified in all 19 symptomatic relatives, all 5 'possibly affected' relatives, and in 9 clinically unaffected relatives. All symptomatic individuals inherited the mutation from their father, and all asymptomatic individuals inherited it from their mother. Foncke et al. (2006) noted that subtle distal myoclonus of the fingers was a prominent feature in this family.

Associations Pending Confirmation

In a family containing 8 members with myoclonic dystonia, Klein et al. (1999) found heterozygosity for a variation in the DRD2 gene (V154I; 126450.0001); however, Klein et al. (2002) later identified a 5-bp deletion in the SGCE gene (604149.0005) in all 8 affected members. There were 2 unaffected carriers of both mutations. The contribution of each mutation to the clinical phenotype could not be determined, but the phenotype most likely resulted from the SGCE mutation, as Klein et al. (2000) showed that the V154I DRD2 mutant protein was similar to wildtype and did not show impaired activity in in vitro studies. (See also Furukawa and Rajput, 2002).

By direct sequencing, Klein et al. (2000) excluded DRD2 mutations in 5 unrelated probands with myoclonus dystonia. Four additional families were excluded by linkage analysis. Durr et al. (2000) excluded mutations in the DRD2 gene in 9 unrelated families with myoclonic dystonia or essential myoclonus and variable responses to alcohol. The authors concluded that DRD2 mutations are rare in these disorders.

For discussion of a possible association between myoclonic dystonia and variation in the DYT1 (TOR1A) gene, see 605204.0002.

Cytogenetics

Guettard et al. (2008) reported a 35-year-old man with myoclonus-dystonia and Silver-Russell syndrome (SRS; 180860). Cytogenetic analysis identified mosaicism for a small supernumerary ring chromosome derived from the pericentric region of chromosome 7, which was considered unlikely to contribute to the phenotype as it contained only the EGFR gene (131550). Microsatellite analysis indicated loss of the paternal allele and maternal uniparental disomy of chromosome 7 (UPD7) that was maternally imprinted with loss of SGCE expression. There were no mutations in the SGCE gene. The findings indicated that UPD7 resulted in repression of both alleles of the maternally imprinted SGCE gene, suggesting loss of function of SGCE as the disease mechanism.