Juvenile Huntington’s disease (JHD) is a rare, inherited neurological disorder that affects children and adolescents. It represents a small percentage, around 5% to 10%, of all Huntington’s disease cases. JHD involves the progressive breakdown of nerve cells in specific brain regions, leading to a decline in movement control, intellectual abilities, and emotional regulation. This form of the disease is distinct from the more common adult-onset Huntington’s disease, with differences in symptoms and progression.
Recognizing the Signs
JHD symptoms affect motor, cognitive, and behavioral functions. Motor symptoms in children with JHD often differ from those seen in adults. Rather than the involuntary jerking movements known as chorea, children are more likely to experience muscle rigidity, limb stiffness, and slowness of movement, sometimes resembling Parkinson’s disease. They may also exhibit dystonia, which involves abnormal posturing of the head, neck, or limbs, along with tremors, gait disturbances, and difficulty with balance. Speech difficulties, such as slurred speech and drooling, are common.
Cognitive and learning changes are often early indicators of JHD. Children may experience a decline in school performance, struggling with concentration, learning new information, and following instructions. Previously acquired skills may be lost, and difficulties with organization and processing thoughts can become apparent. Affected individuals may take longer to respond to questions or complete tasks, and they may struggle with multitasking and decision-making.
Changes in behavior and emotional regulation are also common in individuals with JHD. These can include mood swings, increased irritability, depression, and shifts in personality. Some children may exhibit attention difficulties, hyperactivity, or impulsive and aggressive behaviors. A distinguishing feature of JHD compared to the adult-onset form is the higher incidence of seizures, particularly in younger children, which can sometimes be the first symptom to appear.
Genetic Inheritance and Cause
Juvenile Huntington’s disease arises from a specific genetic alteration within the huntingtin (HTT) gene, located on chromosome 4. This gene contains a repeating sequence of cytosine, adenine, and guanine (CAG) trinucleotide repeats. While everyone has these CAG repeats, individuals with Huntington’s disease have an abnormally expanded number of them.
For JHD, the number of CAG repeats is much higher, often exceeding 60 repeats. A greater number of these repeats is associated with an earlier age of disease onset and a more rapid progression of symptoms. This phenomenon, where the disease appears at an earlier age and with greater severity in successive generations, is known as “anticipation”.
JHD is most often inherited from the father, with approximately 75% of cases being paternally inherited, due to CAG repeat expansion being more likely during sperm cell formation. This paternal transmission contributes to the observed anticipation in families affected by Huntington’s disease.
The Diagnostic Process
Confirming a diagnosis of juvenile Huntington’s disease involves a structured approach, starting with a thorough clinical evaluation. A neurologist conducts physical and neurological examinations. During this evaluation, the neurologist observes the child’s movements, assesses their cognitive function, and notes any behavioral changes. They look for specific signs such as muscle stiffness, balance issues, and coordination problems.
A detailed family medical history is an important component of the diagnostic process. Knowing if other family members, especially parents, have been diagnosed with Huntington’s disease provides a strong indicator for potential JHD. This genetic predisposition guides further investigation.
Genetic testing provides the definitive confirmation of JHD. This involves a blood test where a sample is analyzed to count the number of CAG repeats within the HTT gene. A genetic counselor discusses the testing process and results with the family, explaining the implications of the repeat count. A diagnosis of JHD is confirmed when clinical signs are present alongside a pathogenic CAG repeat expansion greater than 60 repeats.
Managing Symptoms and Progression
Currently, there is no cure for juvenile Huntington’s disease, so treatment strategies focus on managing symptoms and enhancing the child’s quality of life. A multidisciplinary team provides care, which may include neurologists, psychiatrists, speech-language pathologists, occupational therapists, and physical therapists. Medications can be prescribed to help control various symptoms. For instance, drugs may be used to reduce muscle rigidity, manage seizures, or address mood disturbances like depression and irritability.
Therapeutic support plays an important role in helping children maintain function. Physical therapy helps with movement, balance, and gait, while occupational therapy assists with daily activities and fine motor skills. Speech therapy is beneficial for addressing difficulties with communication and swallowing, which can become more challenging as the disease progresses. Nutritionists can also provide guidance on maintaining adequate weight and addressing feeding difficulties.
Juvenile Huntington’s disease progresses more rapidly than the adult-onset form of the disease. The earlier the onset of symptoms, the faster the disease tends to advance. As the disease progresses, children may require increasing levels of support for daily activities, and ongoing care is necessary for both the affected child and their family to navigate the changing needs and challenges.