Juvenile Huntington’s Disease: An Australian Guide

Juvenile Huntington’s disease: when it starts before twenty

Juvenile Huntington’s disease — onset before the age of 20 — is rare, accounts for somewhere between about 1 and 15 per cent of Huntington’s diagnoses depending on the series, and is routinely diagnosed late because it does not look like Huntington’s disease.

Where adult HD announces itself with chorea, mood change and executive decline, juvenile HD in a young child frequently presents with rigidity, seizures, declining school performance and behaviour problems — and chorea is often absent. A child with new stiffness, falls, seizures and a drop in school results does not immediately suggest a condition most clinicians associate with involuntary writhing movements in middle age.

There is also a specific genetic pattern worth knowing before anything else, because it has consequences for the whole family: juvenile HD is usually caused by a very long CAG repeat, above about 55, and is usually inherited from the father — sometimes from a father who is not yet symptomatic himself.

This guide covers what juvenile HD looks like at different ages, the genetics and what it means for the family, how it is diagnosed and what delays it, the course, and the practical business of school, funding and support for a child or teenager with a progressive neurological disease.

A note on scope. This is a guide written by an adult disability provider, so it is honest about where our usefulness ends. We support NDIS participants, which includes young people, but a child with juvenile HD needs paediatric neurology, a specialist HD service, a school, and family support services working together, and the organisation to ring first is Huntington’s Australia on 1800 244 735.

What it looks like

The presentation differs substantially depending on whether onset is in the first or second decade.

First-decade onset (childhood). The picture is dominated by rigidity and behaviour rather than chorea:

• Behaviour problems, often the first thing noticed
• Declining school performance, frequently over a year or two
• Dysarthria — slurred, difficult speech
• Seizures, which are far more common in juvenile HD than in adult HD and which occur in a substantial proportion of children
• Rigidity and bradykinesia
• Dystonia
• Gait problems, stiffness, falls
• Chorea is less common

This akinetic-rigid presentation is sometimes called the Westphal variant.

Second-decade onset (adolescence). Closer to adult HD, with some additions:

• Depression, frequently
• Suicidal ideation, noted as frequent in the literature for this group
• Obsessive behaviour and perseveration
• Chorea more likely than in the younger group
• Cerebellar ataxia, spasticity, tremor
• Blinking or sniffing tics
• Cognitive and executive decline

The course is faster. Disease duration in juvenile HD is approximately 8 to 12 years, compared with 15 to 18 in adult-onset disease.

And one thing to say plainly to families reading this: the behaviour problems and school decline that typically come first are frequently treated as a disciplinary or psychological matter for a considerable period. Children get labelled as difficult, disengaged or oppositional. Parents get told to be firmer. That is one of the more painful features of the condition and it is worth knowing that it is the usual pattern rather than something your family did wrong.

The genetics, and what it means for the family

Very long repeats. Juvenile HD is usually caused by a CAG repeat length above about 55. The relationship between repeat length and age of onset, which is loose in the common adult range, becomes considerably tighter at these lengths.

Usually paternal. The repeat is more likely to expand when transmitted by a father than a mother, probably because sperm are produced continuously through life with many more rounds of DNA copying, each an opportunity for the repeat to lengthen. The resulting pattern — earlier and sometimes more severe disease in each successive generation — is called anticipation.

Which has three consequences families should be prepared for:

The father may not yet be symptomatic. A child diagnosed with juvenile HD can effectively diagnose a parent who did not know, had not been tested, or had chosen not to be tested. This is one of the hardest things in Huntington’s disease and it is not uncommon.

Siblings are at 50 per cent risk, with the same anticipation considerations.

The wider paternal family — the father’s siblings, and their children — are also implicated, and may learn about their own risk through a child’s diagnosis.

Genetic counselling for the whole family is essential, not optional, and it is free through state genetic services. The counselling needs to cover who knows what, who wants to know, and the fact that predictive testing in well children is not offered — Australian practice sets eligibility at 18, on the basis that the child cannot consent, no treatment follows from knowing, and the right not to know belongs to them. Testing eligibility and the inheritance pattern are covered in Huntington’s genetics and the 50 per cent.

The exception, and it matters here: where a child or adolescent has symptoms consistent with juvenile HD, genetic testing is diagnostic rather than predictive and is entirely appropriate, because it is identifying the cause of a present illness rather than predicting a future one. A family being told that children cannot be tested, in a situation where their child is symptomatic, has been told the wrong thing.

Diagnosis, and what delays it

Why it takes so long. Several reasons stack.

The presentation is atypical. Rigidity, seizures and school decline do not suggest Huntington’s to most clinicians.

Behaviour comes first and is managed as behaviour.

Juvenile HD is rare, so paediatricians may never have seen a case.

Family history is often absent or unknown. The affected parent may not yet be symptomatic, may be unaware, or may be out of contact. “No family history” does not exclude it.

And seizures lead somewhere else. A child with new seizures and developmental decline enters an epilepsy and metabolic pathway, which is reasonable and which may run for a long time before genetics is reached.

What the process involves. Paediatric neurology referral; a detailed family history on both sides, specifically asking about relatives with movement disorders, psychiatric illness, early dementia or unexplained early death; MRI of the brain; EEG where there are seizures; metabolic and genetic investigations; and the HTT gene test. A specialist HD service or clinical genetics service should be involved.

What to say, if you suspect it. “There is Huntington’s disease on my husband’s side” — or “my husband’s father had an undiagnosed neurological illness” — is the single sentence that changes the diagnostic pathway. Say it at the first appointment. If the father’s status is unknown and there is any family suggestion of HD, say that too. And ask directly: “could this be juvenile Huntington’s disease?”

What gets excluded. A wide range of paediatric neurodegenerative and metabolic conditions, Wilson’s disease (treatable), the HD-like syndromes including DRPLA, mitochondrial disease, autoimmune and post-infectious conditions, and structural causes.

School

This is where most of the practical work sits in the years after diagnosis, and it is handled well or badly depending almost entirely on whether the school understands what it is dealing with.

Tell the school properly. Not just the diagnosis — what it means functionally. Progressive. Cognitive as well as physical. Behaviour that is neurological rather than chosen. Likely to need more help each year rather than less.

Ask for a formal support plan. Every state and territory has a mechanism for individual education plans and funded adjustments. Ask for it in writing and ask for it to be reviewed each term rather than annually, because the condition moves faster than an annual cycle.

Expect the adjustments to change constantly. What worked in term one may not work in term three. Writing becomes hard, then impossible; handwriting adjustments give way to scribing or technology. Fatigue rises. Seizures may need a management plan. Speech becomes hard to understand.

Get an occupational therapist and a speech pathologist into the school, not just into the clinic. The school environment is where the adjustments have to work.

Protect the social part. This matters more than the academic part by a considerable margin. A young person with a progressive illness whose friendships are maintained has a better life than one whose grades are maintained. Whatever can be done to keep them in the class, in the group, in the sports team in some capacity, is worth prioritising.

And be realistic about academic expectation, kindly and gradually. A child who was going to be a vet is not going to be a vet. Managing that honestly, as it becomes relevant and not before, is one of the harder parenting tasks in this condition and it is worth doing with psychological support.

Tell the teachers about behaviour specifically. Irritability, perseveration, inflexibility and loss of filter will be read as misbehaviour unless somebody explains. A short written note for every new teacher each year, explaining what the behaviour is and what to do, prevents a great deal of harm.

Funding and support

The NDIS. Huntington’s disease is on List B, meaning permanence is accepted and functional impact must be evidenced. A child with juvenile HD will usually have substantial impairment across multiple domains and should be eligible, but as with adult HD, the cognitive and behavioural impairment is harder to evidence than the physical. Ask for a neuropsychological assessment, a functional report, and a school report describing what support is actually needed in class. See Huntington’s disease and the NDIS.

Ask for the plan to anticipate progression, with the trajectory stated in the clinical letter.

Ask for support coordination.

Ask for therapy funded as a flexible category, because the mix will change — physiotherapy, occupational therapy, speech pathology, psychology, and later dietetics.

Ask for family and sibling support. Siblings of a child with juvenile HD are in an extraordinary position: watching a brother or sister deteriorate, while being at 50 per cent risk themselves, in a family where a parent may also be affected or at risk. That is not a footnote. Counselling for siblings is a legitimate request.

Carer Gateway on 1800 422 737 for the parents, and it is independent of the child’s funding.

Centrelink: Carer Payment, Carer Allowance, and Child Disability Assistance Payment where eligible.

And Huntington’s Australia on 1800 244 735, which is the organisation that knows the Australian landscape for this condition.

Seizures, specifically

Worth its own short section because it is one of the main differences from adult HD.

Seizures occur in a substantial proportion of children with juvenile HD and are uncommon in adult-onset disease. They need managing as epilepsy — paediatric neurology involvement, anticonvulsant treatment, and a written seizure management plan held by the family, the school and any support provider.

Where paid support workers are involved, epilepsy and seizure support is a high intensity support requiring specific competence: workers trained in recognising seizure types, administering any prescribed emergency medication, timing, positioning, and when to call an ambulance. There should be a plan from the treating doctor, documented training, and competency sign-off. Ask any provider who is trained and what happens on a shift when that person is unavailable. The general framework is in epilepsy and seizure support.

Note also that some medications used in HD can interact with anticonvulsants, and that sodium valproate and levetiracetam are used in HD for myoclonus — so the medication picture needs one clinician holding all of it rather than several prescribing separately.

The family position

It is worth naming, because juvenile HD puts families in a situation almost no other illness creates.

A child is deteriorating. The father is probably the carrier and may be becoming unwell himself, or may be well and carrying the knowledge that he passed it on. The siblings are at 50 per cent risk. The mother is frequently the only adult in the household who is not either affected or at risk, and is caring for all of them. And the extended paternal family has just learned something about itself.

Huntington’s Australia’s chief executive described the general HD family position to the ABC in these terms: because the condition is hereditary, children sometimes care for parents before developing symptoms, and parents sometimes care for partners and then children — with “feelings of loss, guilt, anger, burden and helplessness” and deepening isolation.

In juvenile HD that pattern is compressed and inverted.

What helps: genetic counselling for everybody who wants it, psychological support for the parents separately rather than only as carers, specific support for siblings, peer contact with other HD families, and somebody coordinating the whole thing so the family is not the integration layer between eight services. See families and children.

And the guilt, which deserves naming directly. A parent who passed on a gene they did not know they carried, or knew they might carry, frequently carries guilt that is enormous and entirely undeserved. Nobody chooses their genome. That is worth hearing from a professional rather than only from relatives, and it is a reason to ask for individual counselling rather than family counselling alone.

The transition to adult services

A problem specific to juvenile Huntington’s and one families are rarely warned about: the person will age out of paediatric services during their illness, and the handover is frequently where care falls apart.

What changes at 18. Paediatric neurology hands over to adult neurology, which may or may not have HD expertise. The paediatric multidisciplinary team — often a single service that held everything together — is replaced by several separate adult services. School ends, and with it the structure, the social group and the funded adjustments. Consent becomes the young person’s own, which raises capacity questions in somebody with executive impairment. And the family’s role changes legally even where it has not changed practically at all.

What to do about it, starting at about 16:

Ask for a written transition plan. Most states have a formal transition process for young people with complex conditions, and it has to be asked for. It should name the receiving adult clinicians by name.

Get the adult referrals made before the paediatric service closes, not after. Specifically: adult neurology, ideally at a specialist HD service; psychiatry; and a GP who will hold the whole picture.

Reassess the NDIS plan for adult life, because the goals change completely. School supports give way to community participation, day activity, possibly supported employment, possibly housing. This is a different plan rather than the same plan continued.

Sort out the legal documents. Enduring power of attorney and enduring guardianship, done at 18 while capacity is clearest. In juvenile HD, executive and insight changes may already be established, so this is time-critical and may need a capacity assessment.

Replace what school was providing. This is the part most often missed. School was not only education — it was six hours a day of structure, supervision and company. Losing it without a replacement is one of the commonest causes of deterioration in the year after leaving, and the replacement needs designing in advance.

And ask about adult peer support. Huntington’s Australia on 1800 244 735 can connect young adults with others, which matters particularly for somebody whose school friendships have thinned.