Huntington's disease (HD) is caused by a CAG trinucleotide repeat expansion on the HTT gene (chromosome 4p16.3).
CAG Repeats
Classification
<27
Normal — will not develop HD
27–35
Intermediate — generally unaffected, but expansion possible in offspring
36–39
Reduced penetrance — may or may not develop HD
≥40
Full penetrance — will develop HD if they live long enough
Anticipation: With each generation, CAG repeats tend to expand (especially via paternal transmission), causing earlier onset in children. Juvenile HD (<20 years) is almost always from paternal inheritance.
Inheritance Pattern
Autosomal dominant — one copy of the mutant gene causes disease
Each child of an affected parent has 50% risk of inheriting the mutation
No carrier state — if you inherit the ≥40 repeat allele, you will develop HD
Both males and females equally affected
De novo mutations are rare — almost always inherited
Epidemiology
Prevalence 5–7 per 100,000 in European populations; lower in Asian/Middle Eastern populations
Typical onset: 30–50 years (adult form)
Disease duration: 15–20 years from symptom onset to death
Pathology: preferential loss of medium spiny neurons in the striatum (caudate + putamen)
Social worker — financial benefits, carer support, respite care
Palliative care — advance care planning, symptom management in late stages
Advance Care Planning
Advance care planning discussions MUST occur early, while the patient has full mental capacity. Topics include: DNACPR, PEG feeding, future accommodation, and end-of-life wishes.
Lasting Power of Attorney (health and welfare) should be established early
Patient should nominate a trusted decision-maker while they can
Revisit care plans as disease progresses
Involve family in planning — but patient's wishes take precedence
Falls and Injury Risk
Chorea + gait disturbance = high fall risk
Hip protectors, padded environments, specialist seating
Physiotherapy essential for gait and balance
Driving should be assessed — many patients must stop driving early
Dysphagia and Aspiration
Aspiration pneumonia is the most common cause of death in HD. Dysphagia affects almost all patients in later stages.
Modified diet textures (IDDSI framework)
Upright positioning during meals
Small, frequent meals — fatigue from chorea increases aspiration risk
PEG tube — discuss timing proactively; best placed while patient can consent
Oral hygiene is critical to reduce aspiration pneumonia risk
Target BMI ≥20 — weight loss correlates with faster disease progression
High-calorie supplements, fortified foods
Weekly weight monitoring in advanced stages
Suicide Risk
Suicide risk is 4–6× higher in HD patients than the general population. Both symptomatic patients AND gene-positive presymptomatic individuals are at risk. Assess at every clinical contact.
Ask directly about suicidal ideation
Refer to psychiatry if concerns arise
Remove access to means where possible
Support carers — carer burden is extreme
HD in the GCC Context
HD prevalence is lower in Arab/Middle Eastern populations compared to European populations
Consanguinity does NOT increase HD risk — it is autosomal dominant, not recessive
However, consanguinity may concentrate the mutant allele within families if a founder mutation exists
Specialist HD clinics are limited in the GCC — most care is in general neurology departments
Genetic testing and counselling services are expanding but not universally available
Cultural Considerations
Disclosure of genetic information within families can be culturally sensitive — privacy vs family duty tensions
Stigma around psychiatric symptoms may delay mental health support-seeking
Extended family involvement in care planning is common and can be supportive
PGD is available in several GCC countries but religious guidance should be sought by families
Advance care planning in the context of Islamic values — consultation with religious authorities often helpful
Regulatory and Service Landscape
DHA and DOH have genetic counselling licensing requirements
Tetrabenazine available in UAE and Saudi Arabia; deutetrabenazine access varies
Palliative care services growing in GCC — but community palliative care remains limited
Patient support groups (HD-specific) rare in GCC — international online resources important
Autosomal dominant — 50% inheritance risk per child
CHOREA is the hallmark motor feature (involuntary writhing movements)
Psychiatric: depression is the MOST COMMON psychiatric manifestation
Tetrabenazine = drug of choice to reduce chorea
NO disease-modifying treatment exists
Anticipation = longer repeats in next generation = earlier onset
Juvenile HD = almost always from paternal transmission (greater expansion in sperm)
Aspiration pneumonia = most common cause of death
Advance care planning = must happen EARLY while capacity intact
Common Exam Traps
HD is autosomal DOMINANT not recessive — consanguinity does NOT increase risk
Psychiatric symptoms often PRECEDE motor symptoms — do not wait for chorea to suspect HD
Presymptomatic testing requires pretest counselling — never order without it
Tetrabenazine can cause/worsen depression — monitor mood after starting
GCC Clinical Practice Insights
Genetic Counselling Requirements in GCC +
DHA and DOH licensing frameworks require that genetic counselling for predictive testing is conducted by licensed genetic counsellors or clinical geneticists. Pre-test and post-test psychological support must be documented. Telemedicine genetic counselling has expanded access during and after COVID-19.
Tetrabenazine Availability in GCC +
Tetrabenazine is available in UAE and Saudi Arabia for approved indications. Nurses administering tetrabenazine should monitor for depression, suicidality, parkinsonism, and sedation. Dose titration should be guided by a neurologist experienced in movement disorders.
MDT Coordination in GCC Hospitals +
Most HD management in the GCC occurs within general neurology services rather than specialist HD clinics. Nurses play a critical coordination role — linking patients to physiotherapy, speech therapy, dietetics, and social work. Patient advocates and family liaisons are increasingly available in large hospitals.
End-of-Life Considerations in Islamic Context +
Islamic bioethics generally supports palliative care and comfort measures. Prolonging dying artificially without benefit is discouraged. Families are encouraged to involve an Islamic scholar alongside the medical team for complex end-of-life decisions. DNACPR documentation should be sensitive to cultural and religious norms in GCC hospitals.
Practice MCQs
Q1. A patient with Huntington's disease asks about the inheritance risk for their child. What is the correct risk?
Correct answer: C — HD is autosomal dominant. Each child of an affected parent has a 50% chance of inheriting the expanded CAG repeat allele.
Q2. Which is the hallmark motor feature of Huntington's disease?
Correct answer: B — Chorea (from Greek "dance") refers to the involuntary, irregular, flowing writhing movements that are the hallmark feature of HD. Tremor at rest and rigidity are more characteristic of Parkinson's disease.
Q3. A presymptomatic 28-year-old requests predictive genetic testing for HD after their parent was diagnosed. What is the nurse's most important first action?
Correct answer: C — International guidelines (HD Society of America, EHDN) mandate that predictive genetic testing for HD must be preceded by comprehensive pretest genetic counselling (minimum 2–3 sessions) including psychological assessment.
Q4. Which drug is used to reduce choreiform movements in Huntington's disease?
Correct answer: B — Tetrabenazine is a VMAT2 inhibitor that depletes presynaptic dopamine, reducing chorea. Important side effects include depression, suicidality, parkinsonism, and sedation. Mood must be monitored closely.