Huntington Disease Like (Hdl) Syndromes is a progressive neurodegenerative disorder characterized by the gradual loss of neuronal function. This page provides comprehensive information about the disease, including its pathophysiology, clinical presentation, diagnosis, and current therapeutic approaches.
Huntington's Disease-like (HDL) syndromes are a heterogeneous group of rare neurodegenerative disorders that clinically resemble Huntington's Disease (HD) but are caused by distinct
genetic mutations. These conditions are characterized by a triad of movement disorders, cognitive decline, and psychiatric symptoms that overlap significantly with Huntington
disease, yet they result from different underlying genetic etiologies. The HDL syndromes represent important diagnostic considerations in patients presenting with Huntington
disease-like phenotypes but who test negative for the HTT gene expansion12.
Unlike Huntington's Disease, which follows an autosomal dominant inheritance pattern caused by CAG triplet repeat expansions in the HTT gene, the HDL syndromes encompass multiple distinct genetic disorders with various inheritance patterns. Accurate diagnosis is critical for prognosis, genetic counseling, and emerging treatment considerations. Several HDL syndromes have now been characterized with specific genetic causes, while others remain without a known molecular basis3.
| Syndrome |
Gene |
Inheritance |
Key Features |
| HDL1 |
PRNP |
Autosomal dominant |
Rapidly progressive, onset 30-40s |
| HDL2 |
JPH3 |
Autosomal dominant |
African ancestry, rigid-akinetic form |
| HDL3 |
Unknown |
Autosomal recessive |
Childhood onset, severe |
| HDL4 |
TBP |
Autosomal dominant |
SCA17 variant |
| ATP1A3-related |
ATP1A3 |
Autosomal dominant |
Paroxysmal symptoms |
- HDL syndromes without identified genetic cause (approximately 1-2% of HD-like cases)
- Gene: PRNP (prion protein gene) on chromosome 20p13
- Mutation: Octapeptide repeat insertions
- Inheritance: Autosomal dominant
- Age of onset: 30-40 years
- Disease progression: Rapidly progressive
- Motor symptoms: Chorea, dystonia, parkinsonism
- Cognitive decline: Rapidly progressive dementia
- Psychiatric features: Personality changes, psychosis
- Spongiform changes
- Neuronal loss
- Astrocytosis
- Prion protein deposition
- Gene: JPH3 (junctophilin-3) on chromosome 16q24.3
- Mutation: JPH3 expansion (CTG/CAG repeat)
- Inheritance: Autosomal dominant
- Ethnicity: Predominantly affects individuals of African ancestry
- Age of onset: 20-50 years (mean: 33 years)
- Motor symptoms:
- Chorea (less prominent than HD)
- Bradykinesia
- Dystonia
- Parkinsonism (prominent)
- Facial masking
- Cognitive decline: Progressive dementia
- Psychiatric features: Depression, anxiety, irritability, psychosis
- Unique features: Rigid-akinetic presentation more common than in HD
- Striatal atrophy (caudate and putamen)
- Frontal cortical atrophy
- White matter changes
- Reported primarily in families of African descent
- Estimated 1% of HD-like cases in African populations
- Inheritance: Autosomal recessive
- Gene: Unknown (mapped to 4p15.3)
- Age of onset: Childhood (3-14 years)
- Disease progression: Rapid progression
- Motor symptoms: Severe chorea, dystonia
- Cognitive decline: Severe intellectual disability
- Psychiatric features: Behavioral problems
- Additional features: Seizures in some cases
- More severe than classic HD
- Progressive disability
- Reduced life expectancy
- Gene: TBP (TA-box binding protein)
- Mutation: CAG repeat expansions (45-66 repeats)
- Inheritance: Autosomal dominant
- Age of onset: 20-50 years
- Motor symptoms:
- Ataxia
- Chorea
- Dystonia
- Parkinsonism
- Cognitive decline: Progressive dementia
- Psychiatric features: Depression, personality changes
HDL4 is allelic with Spinocerebellar Ataxia Type 17 (SCA17), representing the HD-like phenotype of TBP gene expansions.
- Gene: ATP1A3 (sodium-potassium ATPase subunit alpha-3)
- Inheritance: Autosomal dominant
- Rapid-onset Dystonia Parkinsonism (RDP)
- Sudden onset of dystonia and parkinsonism
- Triggered by stress
- Craniofacial involvement
- Alternating Hemiplegia of Childhood (AHC)
- Paroxysmal hemiplegic episodes
- Developmental delays
- May evolve to fixed dystonia
When evaluating patients with HD-like presentations, consider:
- Huntington's Disease (HTT expansion)
- HDL syndromes (listed above)
- Spinocerebellar ataxias
- Neuroacanthocytosis
- Wilson disease
- Dentatorubral-pallidoluysian atrophy (DRPLA)
- Fragile X-associated tremor/ataxia syndrome (FXTAS)
- Autoimmune encephalitis
- Metabolic disorders
- Infectious diseases
- Toxic exposures
- Vascular Dementia
- Detailed family history: Three-generation pedigree
- Neurological examination: Document all movement disorders
- Neuropsychological testing: Quantify cognitive deficits
- Psychiatric assessment: Evaluate psychiatric symptoms
- HTT expansion testing (first-line)
- If negative:
- JPH3 (HDL2) - especially if African ancestry
- PRNP (HDL1)
- TBP (HDL4/SCA17)
- ATP1A3
- Other SCA panels
- MRI brain to assess striatal and cortical atrophy
- May help differentiate HD from HDL syndromes
- Chorea: Tetrabenazine, deutetrabenazine, valbenazine
- Dystonia: Botulinum toxin, anticholinergics, muscle relaxants
- Parkinsonism: Levodopa, dopamine agonists
- Depression: SSRIs, SNRIs, tricyclic antidepressants
- Psychosis: Atypical antipsychotics
- Irritability: Mood stabilizers, antidepressants
- No disease-modifying treatments
- Supportive care and rehabilitation
- Acetylcholinesterase inhibitors (limited benefit)
- Autosomal dominant: 50% risk to offspring
- Autosomal recessive: 25% risk to offspring
- Discuss implications for family members
- Multidisciplinary team approach
- Physical therapy for mobility
- Occupational therapy for daily activities
- Speech therapy for dysarthria
- Nutritional support
Prognosis varies by HDL subtype:
- HDL1: Rapid progression, ~10-year disease duration
- HDL2: Similar to HD, 15-20 year disease duration
- HDL3: Severe, often shorter survival
- HDL4: Variable, generally slower progression
- Neurofilament light chain (NfL) as progression marker
- Imaging biomarkers for disease tracking
- Gene silencing strategies
- Prion protein targeting (HDL1)
- JPH3-targeted therapies
- Symptomatic drug development
- Ongoing studies for HDL2
- Prion Disease trials may benefit HDL1
- Symptomatic therapy trials
The study of Huntington Disease Like (Hdl) Syndromes has evolved significantly over the past decades. Research in this area has revealed important insights into the underlying mechanisms of neurodegeneration and continues to drive therapeutic development.
Historical context and key discoveries in this field have shaped our current understanding and will continue to guide future research directions.
- Wild EJ, Tabrizi SJ. Huntington's Disease phenocopy syndromes. Curr Opin Neurol. 2007;20(6):681-687.
- Schneider SA, Walker RH, Bhatia KP. The Huntington's Disease-like syndromes: what to consider in patients with a negative Huntington's Disease gene test? Nat Clin Pract Neurol. 2007;3(9):517-525.
- Margolis RL, Holmes SE, Rosenblatt A, et al. Huntington's Disease-like 2 (HDL2) in North America and Japan. Ann Neurol. 2004;56(5):670-674.
- Butler JS, Chan A, Costantini R, et al. Biochemical analysis of JPH3 expansions in HDL2. J Neurol Sci. 2009;285(1-2):82-88.
- Kurosaki T, Martin JP, Yuasa Y, et al. Octapeptide repeat insertions in PRNP in four cases of disease. Neurology. 2004;62(12):2093-2100.
- Lanska DJ, Lanska MJ. Huntington's Disease-like 2: a model for neurodegenerative disease. Ann Neurol. 2004;56(5):641-642.
- Schneider SA, Bhatia KP. Huntington's Disease look-alikes. Handb Clin Neurol. 2011;100:125-136.