Expanding the phenomenology of benign hereditary chorea: evolution from chorea to myoclonus and dystonia

Inherited and Acquired Choreas

Chorea is a symptom of a broad array of genetic, structural, and metabolic disorders. While chorea can result from systemic illness and damage to diverse brain structures, injury to the basal ganglia, especially the putamen or globus pallidus, appears to be a uniting features of these diverse neuropathologies. The timing of onset, rate of progression, and the associated neurological or systemic symptoms can often narrow the differential diagnosis to a few disorders. Recognizing the correct etiology for childhood chorea is critical, as numerous disorders in this category are potentially curable, or are remediable, with early treatment.

Recent advances in genetics of chorea

PURPOSE OF REVIEW

Chorea presenting in childhood and adulthood encompasses several neurological disorders, both degenerative and nonprogressive, often with a genetic basis. In this review, we discuss how modern genomic technologies are expanding our knowledge of monogenic choreic syndromes and advancing our insight into the molecular mechanisms responsible for chorea.

RECENT FINDINGS

A genome-wide association study in Huntington's disease identified genetic disease modifiers involved in controlling DNA repair mechanisms and stability of the HTT trinucleotide repeat expansion. Chorea is the cardinal feature of newly recognized genetic entities, ADCY5 and PDE10A-related choreas, with onset in infancy and childhood. A phenotypic overlap between chorea, ataxia, epilepsy, and neurodevelopmental disorders is becoming increasingly evident.

SUMMARY

The differential diagnosis of genetic conditions presenting with chorea has considerably widened, permitting a molecular diagnosis and an improved prognostic definition in an expanding number of cases. The identification of Huntington's disease genetic modifiers and new chorea-causing gene mutations has allowed the initial recognition of converging molecular pathways underlying medium spiny neurons degeneration and dysregulation of normal development and activity of basal ganglia circuits. Signalling downstream of dopamine receptors and control of cAMP levels represent a very promising target for the development of new aetiology-based treatments for chorea and other hyperkinetic disorders.

Benign hereditary chorea, not only chorea: a family case presentation

Background

Benign hereditary chorea is a rare disorder which is characterized by early onset, non-progressive choreic movement disturbance, with other hyperkinetic movements and unsteadiness also commonly seen. Hypothyroidism and lung disease are frequent additional features. The disorder is caused by mutations of the NKX2-1 gene on chromosome 14.

Case presentation

A Norwegian four-generation family with eight affected was identified. All family members had an early onset movement disorder, starting before one year of age with motor delay and chorea. Learning difficulties were commonly reported from early school years. The family presented with choreic movements at rest, but other movements were seen; myoclonus, dystonia, ataxia, stuttering and tics-like movements. All patients reported unsteadiness and ataxic gait was observed in two patients. Videos are provided in the supplementary material. Most affected family members had asthma and a subclinical or clinical hypothyroidism. Sequencing revealed a mutation in the NKX2-1 gene in all eight affected family members.

Conclusions

This is the first Norwegian family with benign hereditary chorea due to a mutation in the NKX2-1 gene, c.671 T > G (p.Leu224Arg). This family demonstrates well the wide phenotype, including dystonia, myoclonus and ataxia.

Electronic supplementary material

The online version of this article (doi:10.1186/s40673-016-0041-7) contains supplementary material, which is available to authorized users.

Benign hereditary chorea related to NKX2-1 with ataxia and dystonia

Benign hereditary chorea (BHC) was originally described in 1967, but it was not until 2002 that linkage analysis and positional cloning identified the causative gene, NKX2-1 (also known as TTF-1).(1,2) The range of manifestations spans from isolated chorea, pulmonary disease, or thyroid dysfunction, with one-third of patients having the full brain-lung-thyroid syndrome.(3) Recent reports have expanded the NKX2-1 phenotype, as patients may present with additional movement disorders such as dystonia and myoclonus.(3) We present a case with early-onset chorea, ataxia, and dystonia.

ADCY5 mutations are another cause of benign hereditary chorea

OBJECTIVE

To determine the contribution of ADCY5 mutations in cases with genetically undefined benign hereditary chorea (BHC).

METHODS

We studied 18 unrelated cases with BHC (7 familial, 11 sporadic) who were negative for NKX2-1 mutations. The diagnosis of BHC was based on the presence of a childhood-onset movement disorder, predominantly characterized by chorea and no other major neurologic features. ADCY5 analysis was performed by whole-exome sequencing or Sanger sequencing. ADCY5 and NKX2-1 expression during brain development and in the adult human brain was assessed using microarray analysis of postmortem brain tissue.

RESULTS

The c.1252C>T; p.R418W mutation was identified in 2 cases (1 familial, 1 sporadic). The familial case inherited the mutation from the affected father, who had a much milder presentation, likely due to low-grade somatic mosaicism. The mutation was de novo in the sporadic case. The clinical presentation of these cases featured nonparoxysmal generalized chorea, as well as dystonia in the most severely affected, but no facial myokymia. We observed significant progression of symptoms in ADCY5 mutation carriers, in contrast to BHC secondary to NKX2-1 mutations. The difference in the clinical course is mirrored by the brain expression data, showing increasing ADCY5 expression in the striatum during brain development, whereas NKX2-1 shows an opposite trend.

CONCLUSIONS

Our study identifies mutations in ADCY5, the gene previously linked to familial dyskinesia with facial myokymia, as a cause of familial and sporadic BHC. ADCY5 genetic analysis should be performed in cases with a benign choreiform movement disorder even in the absence of facial myokymia.

The differential diagnosis of Huntington's disease-like syndromes: 'red flags' for the clinician

A growing number of progressive heredodegenerative conditions mimic the presentation of Huntington's disease (HD). Differentiating among these HD-like syndromes is necessary when a patient with a combination of movement disorders, cognitive decline, behavioural abnormalities and progressive disease course proves negative to the genetic testing for HD causative mutations, that is, IT15 gene trinucleotide-repeat expansion. The differential diagnosis of HD-like syndromes is complex and may lead to unnecessary and costly investigations. We propose here a guide to this differential diagnosis focusing on a limited number of clinical features ('red flags') that can be identified through accurate clinical examination, collection of historical data and a few routine ancillary investigations. These features include the ethnic background of the patient, the involvement of the facio-bucco-lingual and cervical district by the movement disorder, the co-occurrence of cerebellar features and seizures, the presence of peculiar gait patterns and eye movement abnormalities, and an atypical progression of illness. Additional help may derive from the cognitive-behavioural presentation of the patient, as well as by a restricted number of ancillary investigations, mainly MRI and routine blood tests. These red flags should be constantly updated as the phenotypic characterisation and identification of more reliable diagnostic markers for HD-like syndromes progress over the following years.

Myoclonus-dystonia syndrome due to tyrosine hydroxylase deficiency

OBJECTIVE

To present a new family with tyrosine hydroxylase deficiency (THD) that presented with a new phenotype of predominant, levodopa-responsive myoclonus with dystonia due to compound heterozygosity of one previously reported mutation in the promoter region and a novel nonsynonymous mutation in the other allele, thus expanding the clinical and genetic spectrum of this disorder.

METHODS

We performed detailed clinical examination of the family and electrophysiology to characterize the myoclonus. We performed analysis of the TH gene and in silico prediction of the possible effect of nonsynonymous substitutions on protein structure.

RESULTS

Electrophysiology suggested that the myoclonus was of subcortical origin. Genetic analysis of the TH gene revealed compound heterozygosity of a point mutation in the promoter region (c.1-71 C>T) and a novel nonsynonymous substitution in exon 12 (c.1282G>A, p.Gly428Arg). The latter is a novel variant, predicted to have a deleterious effect on the TH protein function and is the first pathogenic TH mutation in patients of African ancestry.

CONCLUSION

We presented a THD family with predominant myoclonus-dystonia and a new genotype. It is important to consider THD in the differential diagnosis of myoclonus-dystonia, because early treatment with levodopa is crucial for these patients.