H-ABC
Hypomyelinating Leukodystrophy With Atrophy of the Basal Ganglia and Cerebellum (H-ABC; HLD6) and Autosomal Dominant Torsion Dystonia 4 (DYT4)
Gene: TUBB4A (also known as TUBB4, TUBB5)
Protein: tubulin, beta 4
Clinical Characteristics
H-ABC
- Also known as hypomyelinating leukodystrophy 6
- Infancy to early childhood onset
- Developmental delay
- Progressive deterioration of motor skills
- Extrapyramidal movement disorders:
- Dystonia
- Choreoathetosis
- Rigidity
- Opisthotonus
- Oculogyric crises
- Progressive spastic tetraplegia
- Ataxia
- Cognition relatively preserved
- MRI features:
- Hypomyelination
- Cerebellar atrophy
- Absence or disappearance of putamen
DYT4
- Onset in second to fourth decade
- Progressive spasmodic “whispering” dysphonia
- Cervical or generalized dystonia
- Characteristic “hobby horse” gait ataxia
- Normal MRI
Inheritance pattern: Autosomal dominant or sporadic
What Can Be Learned From This Test
Testing is performed by sequencing the entire coding region of the TUBB4A gene. This will detect point mutations, small deletions and small insertions. It will not detect a partial or whole gene deletion or duplication.
Targeted mutation analysis for the common mutations c.745G>A; p.Asp249Asn in H-ABC or c.4C>G; p.Arg2Gly in DYT4 can be carried out. Please note on submission form if this targeted approach is being requested.
A negative test result does not rule out a genetic cause of hypomyelinating leukodystrophy, since there are many other genes associated with leukodystrophies, some of which are available for testing in our laboratory.
Sample Requirements
Draw 2ml–4ml of blood in EDTA/purple-top tube (minimum of 1ml–2ml for infants).
Turnaround time: 7-10 business days
CPT Codes and Cost
H-ABC Common Mutation Testing
- Code: 81479
- Cost: $225
Full Gene Sequencing
- Code: 81479
- Cost: $500
DYT4 Common Variant Testing
- Code: 81479
- Cost: $225
Known Variant Testing
- Code: 81479
- Cost: $225
Additional Information
- - H-ABC
- - Dystonia 4