Huntington's disease, formerly known as Huntington's chorea, is a rare, hereditary neurological disorder first described by Georges Huntington, a general practitioner, in 1872. It manifests itself in adulthood as motor, cognitive and psychiatric disorders that progressively worsen.
There are around 10 cases of Huntington's disease per 100,000 individuals. Onset is between the ages of 35 and 50, with the same prevalence in men and women. In 10% of cases, the disease appears before the age of 20.
In France, 18,000 people are affected, of whom only 6,000 currently show symptoms, and around 12,000 carriers of the mutated huntingtin gene remain asymptomatic to this day.
The causes and biological mechanisms of Huntington's disease
Huntington's disease is a hereditary genetic disorder caused by an expansion of a CAG motif in the gene coding for the huntingtin protein. It is transmitted in an autosomal dominant fashion: one heterozygous copy of the expansion is sufficient to develop the disease later in life. Descendants of people with this disease have a 50% risk of inheriting the expansion.
Symptoms and diagnosis of Huntington's disease
Symptoms of Huntington's disease often appear between the ages of 30 and 50, with the onset of motor disorders, including chorea, and anxiety and depressive disorders, which are mainly noticed by family and friends and can be treated with effective symptomatic therapy once the symptoms have set in.
Motor symptoms generally include abnormal, abrupt, jerky, involuntary movements of all 4 limbs, impaired balance and dysarthria. From a cognitive point of view, patients experience a slowdown in information processing, difficulty in planning actions and, over time, memory and concentration problems.
These problems are rapidly associated with behavioural disorders such as irritability, anxiety and apathy, leading to a subcortico-frontal syndrome.
The initial diagnosis is based on the signs presented by the patients and can be confirmed by genetic analysis, of which the family must be informed beforehand. Once the expansion has been identified, the families concerned can seek genetic counselling to find out whether or not they are carriers of the mutation, and can consequently undergo prenatal or pre-implantation diagnosis in the event of a parental project.
Treatments for Huntington's disease
There is no cure for Huntington's disease, but various symptomatic treatments can be suggested. Suitable neuroleptics, dopaminergic inhibitors and antidepressants reduce motor and psychiatric signs and sleep disorders. Physiotherapy and speech therapy are necessary and effective. Psychological counselling is important, both for managing the symptoms of the disease and for supporting the patient and his or her family. Social support is crucial.
