Partial loss of function of colony-stimulating factor 1 receptor in a patient with white matter abnormalities

Abstract

Background and purpose: Mutations in colony-stimulating factor 1 receptor (CSF1R) cause adult-onset leukoencephalopathy with axonal spheroids and pigmented glia (ALSP). Patients with ALSP can be misdiagnosed as having acute ischemic stroke due to hyperintensity lesions on diffusion-weighted magnetic resonance imaging. Mutant CSF1R proteins identified in ALSP show a complete loss of autophosphorylation of CSF1R.

Methods: We conducted mutation screening of CSF1R in 123 patients with definite acute ischemic cerebrovascular syndrome and positive family history of stroke. The pathogenicity of identified variants was evaluated using functional analyses. The levels of autophosphorylation of CSF1R in response to treatment with ligands of CSF1R were examined in cells transfected with wild-type and mutant CSF1R.

Results: We identified eight CSF1R variants, six were known non-pathogenic polymorphisms, whereas the other two were missense variants inducing substitution of amino acid residues (p.Glu573Lys and p.Gly747Arg). Functional assay showed that the levels of autophosphorylation of p.Gly747Arg were similar to those of wild-type when treated with ligands. The autophosphorylation of p.Glu573Lys was detectable, but significantly decreased compared with those of wild-type CSF1R (P < 0.001, two-way anova with Bonferroni). The clinical presentation of the patient with p.Glu573Lys was consistent with cerebral embolism. The patient did not have typical clinical findings of ALSP. However, periventricular white matter abnormalities, unrelated to the recent infarct, were evident on brain magnetic resonance imaging.

Conclusions: In contrast to ALSP-associated missense mutations, CSF1R p.Glu573Lys variant in a patient with acute ischemic cerebrovascular syndrome showed a partial loss of autophosphorylation of CSF1R; its clinical significance warrants further investigation.

Keywords: adult-onset leukoencephalopathy with axonal spheroids and pigmented glia; colony-stimulating factor 1 receptor; genetic and inherited disorders; leukodystrophies; leukoencephalopathies; stroke; white matter.

Figure 1. A Schematic Drawing of CSF1R Gene and Protein Domain Structures

Only regions of interest of CSF1R are provided. ex indicates exon; JMD, juxtamembrane domain; KID, kinase insert domain; TKD, tyrosine kinase domain; TM, transmembrane domain; and UTR, untranslated region.

Figure 2. Functional Assay of the CSF1R variants

(A) Immunoblot analyses of total and phosphorylated forms of the variants CSF1R, which were transiently expressed in HEK293T cells cultured in the medium containing 10% FBS. The CSF1R variant of p.Ile794Thr was previously shown to diminish autophosphorylation of CSF1R [7]. (B) Quantification of immunoblot data revealed the levels of autophosphorylation in the p.Glu573Lys variant were significantly decreased at Tyr546, Tyr798, and Tyr923 (n=3). **, P<0.01 versus WT by one-way ANOVA with Tukey.

Figure 3. Functional Assay of the CSF1R Variants in a Condition Treated with IL-34

(A) Immunoblot analyses of ligand-dependent autophosphorylation of CSF1R variants. The CSF1R variant of p.Ile794Thr was previously shown to diminish autophosphorylation of CSF1R [7]. (B) Quantification of immunoblot data revealed that autophosphorylations of CSF1R at p.Tyr546, p.Tyr708, and p.Tyr923 were significantly suppressed in the p.Glu573Lys variant compared with wild-type (n=3). ***, P<0.001; **, P<0.01; *, P<0.05 versus wild-type by two-way ANOVA with Bonferroni.

Figure 4. Brain MRI/CT Images in a Patient with p.Glu573Lys Variant

Axial diffusion-weighted images demonstrate acute infarction in the left cerebellum, the left lateral temporal and parietal cortices, and the right parietal subcortical area (A–C). The lamina necrosis in the left parietal cortex associated with the infarction is evident on T1-weighted image (D). Periventricular white matter hyperintense lesions, which appeared to be greater than expected for the patient’s age, are shown on axial fluid-attenuated inversion recovery images (E, F). The corpus callosum is slightly atrophic on a sagittal T1-weighted image but considered to be normal for the patient’s age (G). Brain CT scan with 5-mm section thickness shows no apparent calcifications (H).