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Kidd's Disease (Huntington’s Disease‑Like 2)

Overview

Kidd’s disease, also known as Huntington’s disease‑like 2 (HDL2), is a rare, autosomal‑dominant neurodegenerative disorder that mimics many features of classic Huntington’s disease (HD). It is caused by a repeat expansion in the JPH3 gene on chromosome 16. Symptoms typically appear in adulthood and progress over 10‑20 years, leading to motor, cognitive, and psychiatric problems.

Although the disease is worldwide, the majority of reported cases are in individuals of African‑American ancestry, where the prevalence is estimated at ≈ 1‑2 per 100,000 people. In the general population the overall prevalence is less than 1 per 100,000, making it one of the rarest HD‑mimic disorders.<sup>[1] Mayo Clinic</sup>

Symptoms

The clinical picture overlaps with Huntington’s disease but has some distinguishing clues. Symptoms are usually grouped into three domains.

Motor Symptoms

• Chorea – involuntary, dance‑like movements of the limbs, face, and trunk.
• Dystonia – sustained muscle contractions causing abnormal postures.
• Bradykinesia – slowed voluntary movements, often mistaken for Parkinsonism.
• Spasticity – increased muscle tone that can lead to stiffness.
• Impaired gait and balance – frequent falls, a wide‑based gait, or shuffling steps.
• Speech & swallowing difficulties (dysarthria, dysphagia) – develop as the disease advances.

Cognitive Symptoms

• Gradual decline in executive function (planning, organizing).
• Memory problems, especially for recent events.
• Reduced processing speed.
• Impaired insight – patients may be unaware of their deficits.

Psychiatric Symptoms

• Depression and apathy – reported in >60 % of cases.
• Obsessive‑compulsive behaviors.
• Irritability, aggression, or anger outbursts.
• Psychosis (hallucinations or delusions) – less common but documented.

Other Features

• Weight loss despite adequate caloric intake (often due to dysphagia and increased energy expenditure).
• Sleep disturbances, including insomnia and REM‑behavior disorder.
• Peripheral neuropathy is rare but has been described.

Causes and Risk Factors

Kidd’s disease is caused by an abnormal expansion of a CTG/CAG repeat in the JPH3 (junctophilin‑3) gene. In unaffected individuals the repeat size ranges from 6‑28 units; affected persons typically have > 40 repeats, often exceeding 70.

Genetic Mechanism

• Autosomal‑dominant inheritance – each child of an affected parent has a 50 % chance of inheriting the mutation.
• Anticipation – the repeat may expand in subsequent generations, leading to earlier onset or more severe disease.

Who Is at Risk?

• People with a family history of HD‑like neurodegeneration, especially of African‑American descent.
• Individuals whose blood test shows the JPH3 repeat expansion.
• Carriers are asymptomatic until the repeat length reaches the pathogenic threshold; thus, genetic testing is the only way to identify at‑risk persons before symptoms appear.

Diagnosis

Because the signs resemble Huntington’s disease, a systematic evaluation is essential.

Clinical Assessment

• Detailed neurologic exam focusing on chorea, dystonia, gait, and cognition.
• Psychiatric interview to document mood and behavioral changes.
• Family pedigree to assess inheritance pattern.

Genetic Testing

The confirmatory test is a quantitative PCR or Southern blot that measures the number of CTG/CAG repeats in the JPH3 gene. A repeat count > 40 is diagnostic for HDL2.<sup>[2] NIH Genetics Home Reference</sup>

Neuroimaging

• MRI – shows caudate and putamen atrophy similar to HD; may also reveal frontal‑white‑matter changes.
• FDG‑PET – reduced glucose metabolism in the basal ganglia and cortex.

Additional Tests

• Blood work to rule out metabolic causes (thyroid, B12, copper).
• Electroencephalogram (EEG) if seizures or severe sleep disturbances are present.

Treatment Options

There is currently **no disease‑modifying therapy** for Kidd’s disease; treatment is symptomatic and supportive.

Medications

• Chorea – Tetrabenazine or deutetrabenazine (VMAT2 inhibitors) reduce involuntary movements.<sup>[3] Cleveland Clinic</sup>
• Parkinsonian features – Low‑dose levodopa or dopamine agonists may help bradykinesia.
• Depression / Anxiety – SSRIs (e.g., sertraline) or SNRIs; consider psychotherapy.
• Psychosis – Atypical antipsychotics (e.g., risperidone) at the lowest effective dose.
• Weight loss – Appetite stimulants (e.g., mirtazapine) or high‑calorie nutritional supplements.

Procedures & Therapies

• Physical & occupational therapy – improve gait, balance, and ADL (activities of daily living) independence.
• Speech‑language therapy – address dysarthria and safe swallowing techniques.
• Deep brain stimulation (DBS) – experimental for severe chorea; data are limited.
• Psychosocial support – counseling, support groups, and caregiver training.

Lifestyle & Home Measures

• Regular aerobic exercise (30 min, 5 days/week) to maintain mobility and mood.
• Balanced diet rich in protein and healthy fats; consider nutritionist guidance.
• Avoid alcohol and sedatives that may worsen balance.
• Use adaptive equipment (grab bars, weighted utensils) to increase safety.

Living with Kidd's disease (Huntington’s disease‑like 2)

Living with a progressive neurodegenerative disorder is challenging, but proactive strategies can preserve quality of life.

Daily Management Tips

1. Establish a routine – predictable schedules reduce anxiety and help with memory.
2. Medication adherence – use pill organizers or electronic reminders.
3. Safety-proof the home – remove tripping hazards, install night‑lights, and consider a medical alert system.
4. Stay socially engaged – regular contact with friends, support groups, or virtual communities lessens isolation.
5. Monitor nutrition and weight – weekly weigh‑ins; involve a dietitian if weight loss exceeds 5 % body weight.
6. Exercise cognition – puzzles, reading, or computer‑based brain training can slow cognitive decline.
7. Plan for progressive care – discuss future care preferences early with family and a healthcare proxy.

Caregiver Guidance

• Learn safe transfer techniques to prevent back injuries.
• Utilize respite services and community resources (e.g., Area Agency on Aging).
• Maintain own health; caregiver burnout is a documented risk.

Prevention

Because Kidd’s disease is genetic, primary prevention is not possible. However, certain steps can reduce the impact for at‑risk individuals.

• Genetic counseling – Recommended for anyone with a family history; counselors can explain inheritance, testing options, and reproductive choices (e.g., pre‑implantation genetic diagnosis).
• Early detection – Baseline neuropsychological testing and MRI in asymptomatic carriers can identify subtle changes, allowing earlier symptomatic treatment.

Complications

If left uncontrolled, the disease can lead to serious complications:

• Falls and fractures – due to gait instability and chorea.
• Pneumonia – aspiration secondary to dysphagia.
• Severe weight loss/malnutrition – worsens weakness and immunity.
• Depression with suicidal ideation – requires urgent psychiatric care.
• Incontinence – may lead to skin breakdown and infection.
• Cognitive decline severe enough to require full‑time supervision – increased risk of neglect or injury.

When to Seek Emergency Care

Prompt medical attention can prevent life‑threatening complications and provide rapid symptom control.

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References

1. Mayo Clinic. “Huntington disease–like 2 (HDL2).” Accessed 2024.
2. National Institutes of Health, Genetics Home Reference. “JPH3 Gene.” 2023.
3. Cleveland Clinic. “Tetrabenazine for Huntington’s Disease and Other Chorea.” 2022.
4. World Health Organization. “Genetic counseling in rare neurodegenerative disorders.” 2021.

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