DEPDC5-Related Epilepsy

DEPDC5-Related Epilepsy

Overview

DEPDC5-related epilepsy is a genetic disorder caused by heterozygous loss-of-function variants in the DEPDC5 gene. This condition is part of the broader spectrum of mTORopathies and is one of the most common genetic causes of focal epilepsy. Patients typically present with focal seizures, often with a temporal lobe focus, and may have comorbid intellectual disability and psychiatric features. Importantly, DEPDC5 variants can also cause familial focal epilepsy, with some carriers being asymptomatic or mildly affected.

DEPDC5 (DEP Domain Containing 5) is a component of the GATOR1 complex, which negatively regulates mTORC1 signaling. Loss-of-function variants lead to dysregulated mTORC1 activity, causing neuronal hyperexcitability and impaired synaptic plasticity.

Genetics and Molecular Basis

DEPDC5 Gene

[DEPDC5](/genes/depdc5) (DEP Domain Containing 5) is located on chromosome 22q12.2 and encodes the DEPDC5 protein, a member of the GATOR1 complex. The gene spans approximately 150 kb and contains 43 exons. Over 200 pathogenic variants have been identified, with the majority being:

• Nonsense variants (~35%): premature stop codons leading to truncated proteins
• Frameshift variants (~30%): indels causing reading frame shifts
• Splice site variants (~25%): aberrant mRNA processing
• Missense variants (~10%): amino acid substitutions affecting function

DEPDC5-Related Epilepsy

Overview

DEPDC5-related epilepsy is a genetic disorder caused by heterozygous loss-of-function variants in the DEPDC5 gene. This condition is part of the broader spectrum of mTORopathies and is one of the most common genetic causes of focal epilepsy. Patients typically present with focal seizures, often with a temporal lobe focus, and may have comorbid intellectual disability and psychiatric features. Importantly, DEPDC5 variants can also cause familial focal epilepsy, with some carriers being asymptomatic or mildly affected.

DEPDC5 (DEP Domain Containing 5) is a component of the GATOR1 complex, which negatively regulates mTORC1 signaling. Loss-of-function variants lead to dysregulated mTORC1 activity, causing neuronal hyperexcitability and impaired synaptic plasticity.

Genetics and Molecular Basis

DEPDC5 Gene

[DEPDC5](/genes/depdc5) (DEP Domain Containing 5) is located on chromosome 22q12.2 and encodes the DEPDC5 protein, a member of the GATOR1 complex. The gene spans approximately 150 kb and contains 43 exons. Over 200 pathogenic variants have been identified, with the majority being:

• Nonsense variants (~35%): premature stop codons leading to truncated proteins
• Frameshift variants (~30%): indels causing reading frame shifts
• Splice site variants (~25%): aberrant mRNA processing
• Missense variants (~10%): amino acid substitutions affecting function

Pathophysiology

DEPDC5 is a key regulator of mTORC1 signaling:

The "mTORopathy" model suggests that DEPDC5 loss leads to constitutive mTORC1 activation, particularly in neurons, causing focal hyperexcitability and seizures[@depdc5_pathophys_2021].

Epidemiology

| Metric | Value |
|--------|-------|
| Prevalence | ~1:50,000–100,000 (estimated) |
| Incidence | Unknown (underdiagnosed) |
| Sex ratio | Equal distribution (1:1) |
| Family recurrence | High (autosomal dominant, incomplete penetrance) |
| Mutational origin | ~80% inherited, ~20% de novo |

DEPDC5 is among the most common genes causing genetic focal epilepsy, accounting for approximately 5-10% of familial epilepsy cases.

Clinical Presentation

Seizure Characteristics

Epilepsy onset typically occurs between ages 2-40 years, with a median onset in adolescence (12-15 years). However, onset can occur in early childhood:

• Focal seizures (most common, >90% of cases)
• Focal impaired awareness seizures (temporal lobe pattern)
• Focal to bilateral tonic-clonic seizures
• Autonomic seizures (tachycardia, flushing)
• Seizures during sleep (very common, >50% of patients)

Developmental and Cognitive Profile

• Intelligence: Usually normal; 20-30% have intellectual disability
• Language: Typically normal
• Behavior: Psychiatric comorbidities in 30-40% (anxiety, depression, ADHD)
• Autism spectrum features: Present in ~15-20%
• Head circumference: Macrocephaly in ~20%

Associated Features

• Sleep-related epilepsy: Over 50% of seizures occur during sleep
• Focal cortical dysplasia: Detected on MRI in ~20% of patients
• Familial occurrence: Multiple affected family members in ~60% of cases
• Variable penetrance: Many carriers are asymptomatic

Diagnosis

Genetic Testing

DEPDC5-related epilepsy is diagnosed through molecular genetic testing:

• Epilepsy gene panel: Most patients identified via panel testing
• Whole exome sequencing: Can identify DEPDC5 variants
• Genome sequencing: May detect structural variants

Electroencephalography

EEG findings include:

• Temporal lobe interictal epileptiform discharges (most common)
• Frontocentral or occipital discharges
• Normal EEG in up to 30% of patients
• Sleep activation of epileptiform activity (common)

Neuroimaging

• MRI: Usually normal; focal cortical dysplasia in ~20%
• PET: Hypometabolism in temporal lobe may be seen
• HSAM: Not typically associated with DEPDC5

Clinical Criteria

Diagnosis requires:

Current Treatment Landscape

Anti-Seizure Medications

Response rates are moderate (~40% achieve seizure freedom):

| Medication | Response Rate | Notes |
|------------|---------------|-------|
| Carbamazepine | ~50% | Often first-line for focal epilepsy |
| Levetiracetam | ~40% | Broad-spectrum, well-tolerated |
| Valproic acid | ~40% | May be effective |
| Lacosamide | ~35% | May help with focal seizures |
| Fenfluramine | Variable | Not specifically studied |
| Cannabidiol | Variable | Limited data |

Patients with mTORopathies may respond to mTOR inhibitors (everolimus, sirolimus).

Non-Pharmacological Treatments

• Ketogenic diet: May be helpful in some patients
• Vagus nerve stimulation: For refractory cases
• Epilepsy surgery: Applicable if focal cortical dysplasia identified
• Laser ablation: For hypothalamic hamartomas (if present)

mTOR Inhibitors

Everolimus or sirolimus may be considered for patients with:

• Refractory seizures
• Associated focal cortical dysplasia
• Comorbid tuberous sclerosis features

Standard of Care Recommendations

Gene Therapy Considerations

Rationale

DEPDC5 is a compelling target for gene therapy:

Technical Challenges

Preclinical Data

Mouse models of Depdc5 haploinsufficiency show:

• Increased seizure susceptibility
• Enhanced mTORC1 signaling
• Abnormal cortical development
• Improved with mTOR inhibitors

Emerging Approaches

| Approach | Stage | Notes |
|----------|-------|-------|
| AAV-DEPDC5 | Preclinical | Gene replacement |
| ASO-mediated knockdown | Discovery | Of mutant allele |
| mTOR inhibitors | Approved for TSC | May help DEPDC5 |

Regulatory Considerations

• Orphan drug designation: Potentially applicable
• Precision medicine: May require patient stratification

Research Landscape

Key Research Groups

| Group | Institution | Focus |
|-------|-------------|-------|
| Baraban Group | UCSF | Epilepsy genetics, GATOR1 |
| Crino Group | Temple University | mTORopathies, FCD |
| Scheffer Group | University of Melbourne | Familial focal epilepsy |
| multiple others | Various | Natural history, therapy |

Natural History Studies

• Epilepsy Genetics Consortium: GATOR1-related epilepsy studies
• FOCAL study: Multi-site natural history of focal epilepsy
• International DEPDC5 Registry: Patient registry

Key Publications

Cross-Links

• [DEPDC5 Gene Page](/genes/depdc5)
• [DEPDC5 Protein](/proteins/depdc5-protein)
• [GATOR1 Complex](/proteins/nprl2-protein)
• [AAV Gene Therapy for Neurodevelopmental Epilepsy](/therapeutics/aav-gene-therapy-neurodevelopmental-epilepsy)
• [Epilepsy Disease Overview](/diseases/epilepsy)
• [Focal Cortical Dysplasia](/diseases/epilepsy)
• [mTOR Pathway Epilepsies](/diseases/tuberous-sclerosis)
• [NPRL2 Gene](/genes/nprl2)
• [NPRL3 Gene](/genes/nprl3)

References