Novel targets for Huntington's disease: future prospects

Pridopidine in the treatment of Huntington's disease

Huntington's disease (HD) is a highly common inherited monogenic neurodegenerative disease, and the gene responsible for its development is located in the 4p16.3 chromosome. The product of that gene mutation is an abnormal huntingtin (Htt) protein that disrupts the neural conduction, thus leading to motor and cognitive disorders. The disease progresses to irreversible changes in the central nervous system (CNS). Although only a few drugs are available to symptomatic treatment, 'dopamine stabilizers' (as represented by the pridopidine) may be the new treatment options. The underlying causes of HD are dopaminergic conduction disorders. Initially, the disease is hyperkinetic (chorea) until it eventually reaches the hypokinetic phase. Studies confirmed a correlation between the amount of dopamine in the CNS and the stage of the disease. Pridopidine has the capacity to be a dopamine buffer, which could increase or decrease the dopamine content depending on the disease phase. A research carried out on animal models demonstrated the protective effect of pridopidine on nerve cells thanks to its ability to alter the cortical glutamatergic signaling through the N-methyl-D-aspartate (NMDA) receptors. Studies on dopamine stabilizers also reported that pridopidine has a 100-fold greater affinity for the sigma-1 receptor than for the D2 receptor. Disturbances in the activity of sigma-1 receptors occur in neurodegenerative diseases, including HD. Their interaction with pridopidine results in the neuroprotective effect, which is manifested as an increase in the plasticity of synaptic neurons and prevention of their atrophy within the striatum. To determine the effectiveness of pridopidine in the treatment of HD, large multicenter randomized studies such as HART, MermaiHD, and PRIDE-HD were carried out.

Irritability in Huntington's Disease

Huntington’s disease (HD) is a heritable and fatal neurodegenerative disease characterized by a triad of motor, cognitive and neuropsychiatric symptoms. A common and particularly detrimental neuropsychiatric alteration in HD gene carriers is irritability, which frequently manifests as abrupt and unpredictable outbursts of anger. This symptom increases the burden of HD in multiple ways, such as jeopardizing employment and straining familial or caregiver support. Although irritability in HD is diagnosed by the administration of standardized rating scales and clinical expertise, measurement of severity and progression is complicated by several factors. Currently, individuals with HD who present with irritability may be managed with a variety of psychotropic medications, primarily antidepressants and antipsychotics. While these therapies offer relief to individuals suffering from irritability in HD, they are often not sufficient. Here, we review irritability in the context of HD and emphasize the need for treatments that are better tailored to mitigate this troublesome symptom. An expeditious strategy in pursuit of this goal involves evaluating the efficacy of approved medications that are used to treat similar neuropsychiatric symptoms.