Eukaryotic Initiation Factor 2B (eIF2B) GEF Activity as a Diagnostic Tool for EIF2B-Related Disorders

Abstract

BackgroundIn recent years, the phenotypes of leukodystrophies linked to mutations in the eukaryotic initiation factor 2B genes have been extended, classically called CACH/VWM (Childhood ataxia with cntral hypomyélination/vanishing white matter disorder). The large clinical spectrum observed from the more severe antenatal forms responsible for fetal death to milder adult forms with an onset after 16 years old and restricted to slow cognitive impairment have lead to the concept of eIF2B-related disorders. The typical MRI pattern with a diffuse CSF-like aspect of the cerebral white matter can lack particularly in the adult forms whereas an increasing number of patients with clinical and MRI criteria for CACH/VWM disease but without eIF2B mutations are found. Then we propose the use of biochemical markers to help in this difficult diagnosis. The biochemical diagnosis of eIF2B-related disorder is difficult as no marker, except the recently described asialotransferrin/transferrin ratio measured in cerebrospinal fluid, has been proposed and validated until now. Decreased eIF2B GEF activity has been previously reported in lymphoblastoid cell lines from 30 eIF2B-mutated patients. Our objective was to evaluate further the utility of this marker and to validate eIF2B GEF activity in a larger cohort as a specific diagnostic test for eIF2B-related disorders.Methodology/Principal FindingsWe performed eIF2B GEF activity assays in cells from 63 patients presenting with different clinical forms and eIF2B mutations in comparison to controls but also to patients with defined leukodystrophies or CACH/VWM-like diseases without eIF2B mutations. We found a significant decrease of GEF activity in cells from eIF2B-mutated patients with 100% specificity and 89% sensitivity when the activity threshold was set at ≤77.5%.ConclusionThese results validate the measurement of eIF2B GEF activity in patients' transformed-lymphocytes as an important tool for the diagnosis of eIF2B-related disorders.

Identification of Residues That Underpin Interactions within the Eukaryotic Initiation Factor (eIF2) 2B Complex

“…Previous studies have postulated that a decrease in eIF2B activity caused by the mutations is responsible for the phenotype (reviewed in Ref. 18) and that the VWM phenotype is correlated with eIF2B activity (20,21). However, we have recently demonstrated that this is not the case, and in fact, some of the most severe VWM mutations have barely any effect on eIF2B activity (16).…”

eIF2B promotes eIF5 dissociation from eIF2•GDP to facilitate guanine nucleotide exchange for translation initiation

“…The mutations affect any eIF2B subunit, and initial reports found that various mutations reduced eIF2B GEF activity (Fogli et al 2004;Li et al 2004;Richardson et al 2004). However, more recent studies have identified eIF2B mutations that do not appear to significantly reduce eIF2B GEF function, despite some being responsible for severe forms of disease (Horzinski et al 2009;Liu et al 2011). Four EIF2B3 (human eIF2Bg) mutants have been analyzed biochemically using purified proteins: L27Q, Q136P, R225Q, and H341Q Matsukawa et al 2011).…”

Functional analysis of recently identified mutations in eukaryotic translation initiation factor 2Bɛ (eIF2Bɛ) identified in Chinese patients with vanishing white matter disease

“…23,24 Measurement of eIF2B GEF activity in patients' transformedlymphocytes was reported to be an important tool for the diagnosis of eIF2B-related disorders. 27 We found that all these recently described eIF2Be mutations in Chinese VWM children resulted in a decrease in eIF2B complex GEF activity. The p.Arg269X and p.Ser610-Asp613del Figure 3 Effects of three EIF2B5 mutations on the Interaction of eukaryotic translation initiation factor 2B (eIF2B)e with other eIF2B subunits.…”

“…However, even within this phenotype, patients differed from each other in age of onset, disease progression and clinical manifestations. Horzinski et al 27 found a weak correlation between GEF activity measured in the eIF2B-mutated lymphoblastoid cell line and age at disease onset. Patient 2, with compound heterozygous mutations p.Arg269X/p.Cys335Ser, showed the most severe phenotype.…”

“…GEF activity was also reported to be significant low (39 ± 7% of control) in a patient's lymphoblast with p.Arg269X heterozygous mutation. 27 Patient 1, with an onset at around 3 years of age, harbored the heterozygous genotype p.Asn376Asp/p.Ser447Leu. p.Ser447Leu was reported in a patient with the most severe antenatal form of VWM, who had a compound heterozygous genotype with another missense mutation, thus may have contributed to the severe phenotype.…”