Health Uncomplicated: What is Huntington's Disease, and How Do I Get a Diagnosis?
What is Huntington’s Disease?
Huntington’s Disease (HD) is a rare, inherited disease that causes the progressive breakdown and death (degeneration) of nerve cells in the brain. It specifically attacks the part of the brain that helps control voluntary movements, and in turn impacts the individual’s functional abilities. This can cause movement, cognitive, and psychiatric symptoms.
The onset of HD typically occurs in the 30s and 40s, and if someone starts experiencing symptoms before age 20, they are considered to have Juvenile Huntington’s Disease.
There is currently no cure for HD, but there are medications available to manage symptoms. (1)
What are the Huntington’s Disease symptoms?
Early signs of HD include mild clumsiness, problems with balance and movement, cognitive and psychological symptoms - this includes symptoms that impact typical thinking and emotion - and behavioral symptoms.
Individuals with HD often develop Chorea, a movement disorder that causes sudden, unintentional, and uncontrollable jerky movements of the arms, legs, torso, and face. (2)
These sudden movements can get more intense when an individual is nervous or distracted. They also can intensify and become more obvious as HD progresses. Chorea also makes it harder to walk and increases the risk of falling.
Not everyone with HD will develop nor experience Chorea. Instead, some individuals may become rigid or stiff, and move very little. This is called Akinesia. (3) Some individuals develop Chorea and will later develop Akinesia. Others develop Dystonia, which is a disorder characterized by involuntary muscle contractions that cause slow repetitive movements or postures. (4) Akinesia and Dystonia can blend or alternate.
Individuals may also experience a mild tremor, or an unintentional back and forth movement, as well as unusual eye movements.
Other symptoms may include:
Physical Symptoms: Slurred speech, difficulty swallowing, eating, speaking, feeding, choking, walking, sleeping, chest infections, loss of energy, fatigue, seizures
Cognitive Symptoms: Loss of judgment, problem solving and decision making skills, trouble driving, prioritizing, organizing, learning new things, remembering facts, putting thoughts into words, and answering questions.
Behavioral Symptoms: Mood swings, irritability, not being active, feeling apathetic or uninterested, feelings of depression and anger. Behavioral symptoms may decrease with progression, however some may experience angry outbursts, thoughts of suicide, deep depression, or psychosis (losing touch with reality).
How does someone get Huntington’s Disease?
Most cases of Huntington’s Disease are inherited. When a parent has HD, each child has a 50% chance of inheriting a copy of chromosome 4 which carries the mutation. If a child doesn’t inherit the mutation, they will not develop the disease, nor will they pass it on to their children. When HD occurs without a family history, this is called sporadic Huntington’s Disease.
HD is caused by a mutation in a gene for protein called huntingtin. This causes the building blocks of DNA - cytosine, adenine, and guanine (CAG) - to repeat more than they should. Someone without HD has 26 copies of CAG. If someone has 27 to 35 copies of CAG, they are not likely to develop HD, but can pass the mutation on to their children, and if someone has 36 or more copies of CAG, they have HD.
How does someone get a Huntington’s Disease Diagnosis?
Doctors use a mixture of diagnostic tests to confirm if an individual has Huntington’s Disease. The testing can include a neurological exam, a family history, a neurophysical exam, a psychiatric evaluation, imaging (CT and/or MRI), and genetic testing.
A neurological exam includes an examination of motor symptoms such as reflexes, muscle strength, balance, sensory symptoms including sense of touch, vision, and hearing, and psychiatric symptoms such as mood.
Neurologists may ask further questions during a neurophysical exam regarding memory, reasoning, mental agility, language skills, and spatial reasoning.
A psychiatric evaluation may include questions about emotional state, behavioral patterns, judgment and coping skills, signs of disordered thinking, and evidence of substance abuse.
Some may use diagnostic imaging such as a CT or MRI. These images show detailed images of the brain and show any changes in the brain of areas affected by Huntington’s Disease. This can also help to rule out other conditions that may cause similar symptoms.
A genetic test is the most effective and accurate method to test for Huntington’s disease. The specific test needed is the direct genetic test, and it counts the number of CAG repeats in the HD gene. Genetic testing can be given to individuals with a family history of the condition, but don’t yet have symptoms. (5)
Prenatal testing is available if there is a family history of HD and if parents are concerned about passing the condition to the child. If there is no family history of Huntington’s Disease, a genetic test is available for the non typical type of the disease. All genetic testing occurs with the consultation of a genetic counselor. (6)