Figure 4: Detection of FRα in CSF by western blotting.

(a) CSF of patients with cerebral folate transport deficiency and controls, respectively, were concentrated tenfold using ‘Amicon Centrifugal Filter Devices’. Thirty micrograms of protein per lane were subjected to SDS–PAGE and western blotting. FRα is absent in the CSF of patients with cerebral folate transport deficiency while it can be clearly detected in the control samples (only one of five different shown). The patients carry the following mutations in the FOLR1 gene: the compound heterozygous mutations p.Q118X/p.C175X and p.C169Y/p.N222S, the homozygous mutations p.C65W and p.169Y and the homozygous splice site mutation g.3576T>G. Full-scan images are displayed in Supplementary Fig. S6. The amount of FRα in the CSF correlates with the concentration of 5MTHF in the CSF (b, c). Two CSF samples from one patient that was diagnosed with KSS, a mitochondrial disorder that is associated with reduced concentration of 5MTHF in the CSF, were compared. The sample with 5MTHF concentration of 39.4 nmol l⁻¹ (reference value: 40–120 nmol l⁻¹) showed a diminished amount of FRα in the CSF, whereas in the second sample the 5MTHF concentration in the CSF was below 5 nmol l⁻¹ and FRα was not detectable (b). CSF samples (100 μg each) from eight additional patients with genetically confirmed KSS were analysed by western blotting. The intensity of the FRα signal roughly correlated with the 5MTHF concentration in the CSF (c). Transferrin served as loading control. Full-scan images are displayed in Supplementary Fig. S6.