Childhood ataxia withcentral nervous system hypomyelination/vanishing white matter disease(CACH/VWM) is characterized by ataxia, spasticity, and variable optic atrophy.The phenotypes range from a prenatal/congenital form to a subacute infantile form (onset age <1 year), an earlychildhood-onset form (onset age 1-5 years), a late childhood-/juvenile-onsetform (onset age 5-15 years), and an adult-onset form. The prenatal/congenital form is characterized by severe encephalopathy. In the later-onset formsinitial motor and mental development is normal or mildly delayed followed byneurologic deterioration with a chronic progressive or subacute course. Chronicprogressive decline can be exacerbated by rapid deterioration during febrileillnesses or following head trauma or major surgical procedures, or by acutepsychological stresses such as extreme fright.
The diagnosis of CACH/VWMcan be made with confidence in individuals with typical clinical findings,characteristic abnormalities on cranial MRI (cerebral hemispheric white matterthat is symmetrically and diffusely abnormal with a signal intensity close toor the same as cerebrospinal fluid), and identifiable mutations in one of fivecausative genes (EIF2B1, EIF2B2, EIF2B3, EIF2B4,and EIF2B5) encoding the five subunits of the eucaryotic translation initiation factor, eIF2B. Mutations have been found in approximately 90% ofindividuals with CACH/VWM using sequence analysis or mutation scanning. Affected individuals are homozygotes or compound heterozygotes for mutations within thesame gene.The percentage of mutations found in each gene is as follows: EIF2B1 4%, EIF2B2 15%, EIF2B3 7%, EIF2B4 17%, EIF2B5 57%. Intrafamilialvariability exists. Heterozygotes (carriers) areasymptomatic. No clinical or MRI abnormalities have been found in carriers formutations in EIF2B1-5.
The prevalence of CACH/VWMis not known; it is considered one of the most common leukodystrophies. In astudy of unclassified leukodystrophies in childhood, CACH/VWM was the mostcommon. "Cree leukoencephalopathy," described in the native NorthAmerican Cree and Chippewayan indigenous population, is now recognized to bethe same as the infantile form of CACH/VWM.
Testing is available foreach gene individually or as a panel.
This test is indicated for:
- Confirmation of a clinical/biochemical diagnosis of CACH/VWM in individuals who have tested negative for sequence analysis
- Carrier testing in adults with a family history of CACH/VWM who have tested negative for sequence analysis
Infants and Young Children (<2 years of age): 2-3 ml
Children > 2 years of age to 10 years old: 3-5 ml
Older Children & Adults: 5-10 ml
Autopsy: 2-3 ml unclotted cord or cardiac blood
Isolation using the Perkin Elmer™Chemagen™ Chemagen™ Automated Extraction method or Qiagen™ Puregene kit for DNA extraction is recommended.
Submit copies of diagnostic biochemical test results with the sample, if appropriate. Contact the laboratory if further information is needed.
Sequence analysis is required before deletion/duplication analysis by targeted CGH array. If sequencing is performed outside of EGL Genetics, please submit a copy of the sequencing report with the test requisition.
- Sequence analysis of the EIF2B1 gene is available and is required before deletion/duplication analysis.
- Sequence and deletion/duplication analysis of each of the EIF2B1-5 genes is available individually or as a panel for carrier testing in those individuals with a partner who is a known carrier.
- Prenatal testing is available to couples who are confirmed carriers of mutations. Please contact the laboratory genetic counselor to discuss appropriate testing prior to collecting a prenatal specimen.