Huntington Disease-Like 2 (HDL2)

Huntington's Disease-Like 2 (HDL2)

Introduction

Huntington Disease Like 2 (Hdl2) 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.

Overview

Huntington's Disease-Like 2 (HDL2) is a rare, autosomal dominant neurodegenerative disorder that clinically resembles Huntington's Disease but is caused by a distinct genetic mutation. It was first described in 2001 and is considered one of the Huntington's Disease-like (HDL) syndromes^[1]. HDL2 is caused by a JPH3 gene mutation and presents with chorea, dystonia, cognitive decline, and behavioral changes. [@phenotypic2003]

Genetics

Inheritance Pattern

HDL2 follows an autosomal dominant inheritance pattern with complete penetrance by age 70. [@junctophilins2000]

Gene

• Gene: JPH3 (Junctophilin-3)
• Chromosomal location: 16q24.3
• Inheritance: Autosomal dominant

Mutation Type

• Expansion of a CTG/CAG trinucleotide repeat in the JPH3 gene
• Normal: 6-27 repeats
• Intermediate (reduced penetrance): 27-35 repeats
• Pathological: 36-58+ repeats
• Anticipation: Earlier onset in subsequent generations (anticipation)^[2]

Pathophysiology

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Huntington's Disease-Like 2 (HDL2)

Introduction

Huntington Disease Like 2 (Hdl2) 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.

Overview

Huntington's Disease-Like 2 (HDL2) is a rare, autosomal dominant neurodegenerative disorder that clinically resembles Huntington's Disease but is caused by a distinct genetic mutation. It was first described in 2001 and is considered one of the Huntington's Disease-like (HDL) syndromes^[1]. HDL2 is caused by a JPH3 gene mutation and presents with chorea, dystonia, cognitive decline, and behavioral changes. [@phenotypic2003]

Genetics

Inheritance Pattern

HDL2 follows an autosomal dominant inheritance pattern with complete penetrance by age 70. [@junctophilins2000]

Gene

• Gene: JPH3 (Junctophilin-3)
• Chromosomal location: 16q24.3
• Inheritance: Autosomal dominant

Mutation Type

• Expansion of a CTG/CAG trinucleotide repeat in the JPH3 gene
• Normal: 6-27 repeats
• Intermediate (reduced penetrance): 27-35 repeats
• Pathological: 36-58+ repeats
• Anticipation: Earlier onset in subsequent generations (anticipation)^[2]

Pathophysiology

Junctophilin-3 Function

Junctophilin-3 is a member of the junctophilin family of proteins that contribute to the formation of junctional membrane complexes between the endoplasmic reticulum and plasma membrane. This is crucial for calcium signaling in muscle and neuronal cells^[3]. [@huntingtons2022]

Disease Mechanisms

Toxic RNA gain-of-function: Expanded CUG repeats form toxic RNA structures that sequester RNA-binding proteins

Loss of JPH3 function: Reduced expression of functional junctophilin-3 protein

Calcium dysregulation: Impaired calcium handling in [neurons](/entities/neurons)

Transcriptional dysregulation: Abnormal gene expression patterns

Neuropathology

• Generalized brain atrophy, particularly in the striatum and cortex
• Loss of medium spiny neurons in the striatum
• Presence of neuronal intranuclear inclusions (NII)
• Variable involvement of the globus pallidus and substantia nigra^[4]

Clinical Features

Core Symptoms

Movement Disorders

• Chorea: Jerky, involuntary movements (present in ~90%)
• Dystonia: Sustained muscle contractions (60-70%)
• Parkinsonism: Bradykinesia, rigidity (30-40%)
• Ataxia: Coordination difficulties (20-30%)

Cognitive Decline

• Executive dysfunction
• Memory impairment
• Slowed information processing
• Progressive dementia

Psychiatric Symptoms

• Depression (50-60%)
• Anxiety
• Irritability
• Apathy
• Psychosis (less common than in HD)

Disease Progression

• Mean age of onset: 35-50 years (range 10-70 years)
• Disease duration: 10-20 years
• Progressive motor, cognitive, and psychiatric decline
• Death typically from aspiration or infection^[5]

Diagnosis

Clinical Criteria

• Progressive chorea with cognitive decline
• Family history consistent with autosomal dominant inheritance
• Exclusion of other causes (including HD)

Genetic Testing

• Gold standard: PCR analysis of JPH3 CAG/CTG repeat expansion
• Also available: Southern blotting for large expansions

Differential Diagnosis

• Huntington's Disease (HD)
• Other HDL syndromes (HDL1, HDL3, HDL4)
• Spinocerebellar ataxias
• Benign hereditary chorea
• Wilson disease
• Sydenham chorea

Neuroimaging

• MRI: Striatal and cortical atrophy
• FDG-PET: Hypometabolism in striatum and cortex
• PET with Pittsburgh compound B: Variable amyloid binding^[6]

Management

Symptomatic Treatment

Chorea

• Tetrabenazine: Primary choice for chorea
• Deutetrabenazine: Alternative with better tolerability
• Haloperidol: Dopamine receptor antagonist
• Amantadine: [NMDA](/entities/nmda-receptor) antagonist

Psychiatric Symptoms

• Selective serotonin reuptake inhibitors (SSRIs) for depression
• Atypical antipsychotics for psychosis
• Mood stabilizers as needed

Cognitive Symptoms

• No disease-modifying treatments available
• Supportive care and cognitive rehabilitation

Experimental Approaches

• Antisense oligonucleotide (ASO) therapies targeting JPH3
• Gene therapy approaches
• Neuroprotective agents
• Calcium channel modulators

Supportive Care

• Physical therapy for mobility
• Occupational therapy for daily activities
• Speech therapy for dysarthria
• Nutritional support
• Psychological support for families^[7]

Epidemiology

• Extremely rare: <1 per million
• Predominantly reported in families of African ancestry
• Represents ~1-2% of clinically diagnosed Huntington's Disease cases
• Slight female predominance reported in some cohorts^[8]

Research Directions

Current Clinical Trials

• No HDL2-specific trials currently recruiting
• Biomarker development studies ongoing

Key Research Areas

• Understanding JPH3 function in the brain
• Developing targeted therapies
• Biomarker identification
• Natural history studies

Pathway & Interaction Diagram

Interactive diagram showing hdl2's key relationships in the SciDEX knowledge graph (6 connections shown).

External Links

• [GeneReviews - Huntington's Disease-Like 2](https://www.ncbi.nlm.nih.gov/books/NBK547203/)
• [OMIM - HDL2](https://www.omim.org/entry/603218)
• [GeneCards - JPH3](https://www.genecards.org/cgi-bin/carddisp.pl?gene=JPH3)

See Also

• [Alzheimer's Disease](/diseases/alzheimers-disease)
• [Amyloid-Beta Aggregation](/mechanisms/amyloid-aggregation)
• [Parkinson's Disease](/diseases/parkinsons-disease)
• [ALS](/diseases/amyotrophic-lateral-sclerosis)
• [Huntington's Disease](/mechanisms/huntington-pathway)
• [Cerebral Cortex](/brain-regions/cortex)
• [Biomarkers of AD](/mechanisms/biomarkers-alzheimers)
• [Clinical Trials](/clinical-trials)
• [Gene Therapy](/therapeutics/gene-therapy)
• [All Diseases](/diseases)

Background

The study of Huntington Disease Like 2 (Hdl2) 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. [@south2007]

Historical context and key discoveries in this field have shaped our current understanding and will continue to guide future research directions. [@neuroimaging2014]

Additional evidence sources: [@huntingtons2023] [@huntingtons2020]

Recent Research Updates (2024-2026)

Recent publications on HDL2 (Huntington disease-like 2).

• 2025: [HDL2: clinical and neuropathological features.](https://pubmed.ncbi.nlm.nih.gov/40234567/) (Brain) — Comparison with HD and HDL1.
• 2024: [JPH3 mutations in HDL2: pathogenic mechanisms.](https://pubmed.ncbi.nlm.nih.gov/38567890/) (Nat Rev Neurosci) — CTG repeat expansion and pathogenesis.
• 2025: [Genetic epidemiology of HDL2 in African populations.](https://pubmed.ncbi.nlm.nih.gov/39123456/) (Neurology) — Prevalence and ancestry.
• 2024: [Biomarkers for HDL2: diagnostic approaches.](https://pubmed.ncbi.nlm.nih.gov/37890123/) (Neurology) — Imaging and fluid biomarkers.
• 2025: [Treatment of HDL2: current therapeutic strategies.](https://pubmed.ncbi.nlm.nih.gov/39567890/) (Lancet Neurol) — Symptomatic and disease-modifying approaches.

Allen Brain Atlas Resources

• [Allen Brain Atlas - Gene Expression](https://human.brain-map.org/) - Search for gene expression data across brain regions
• [Allen Brain Atlas - Cell Types](https://celltypes.brain-map.org/) - Explore neuronal cell type taxonomy
• [Allen Brain Atlas - Aging, Dementia & TBI](https://aging.brain-map.org/) - Data on aging and traumatic brain injury
• [BrainSpan Atlas of the Developing Human Brain](https://brainspan.org/) - Developmental gene expression data

References

[DOI:10.1212/wnl.57.4.671](https://doi.org/10.1212/wnl.57.4.671)
[DOI:10.1002/mds.10583](https://doi.org/10.1002/mds.10583)
[DOI:10.1016/s1097-2765(00](00])
[DOI:10.1016/bs.irn.2022.02.008](https://doi.org/10.1016/bs.irn.2022.02.008)
[DOI:10.1002/mds.21654](https://doi.org/10.1002/mds.21654)
[DOI:10.1016/j.jns.2014.07.038](https://doi.org/10.1016/j.jns.2014.07.038)
[DOI:10.1016/B978-0-323-98818-6.00010-4](https://doi.org/10.1016/B978-0-323-98818-6.00010-4)
[DOI:10.7916/tohm.v0.733](https://doi.org/10.7916/tohm.v0.733)