Cerebral folate deficiency in two siblings caused by biallelic variants including a novel mutation of FOLR1 gene: Intrafamilial heterogeneity following early treatment and the role of ketogenic diet

Mutations in the FOLR1 gene, encoding for the folate alpha receptor (FRa), represent a rare recessive genetic cause of cerebral folate deficiency (CFD), a potentially reversible neurometabolic condition. Patients typically present with developmental delay, seizures, abnormal movements, and delayed myelination. We hereby expand the phenotypic and genotypic spectrum of the disease with the report of the first two Greek siblings that were found compound heterozygous for one known FOLR1 gene mutation (p.Cys65Trp) and a mutation (p.Trp143Arg) that has not yet been reported in the literature (class 3 variant according to ASHG classification). A distinguishing feature of the older sibling is the manifestation of drug‐resistant epileptic spasms beyond infancy. These had a relatively good response to a ketogenic diet, as an additional treatment to topiramate and valproate. A further clinical improvement was observed when folinic acid was combined with the above treatment. While a response to folinic acid is well established in the disorder, the efficacy of its combination with the ketogenic diet needs further evaluation, but we suggest considering it early in the course of drug resistant epilepsy in the setting of CFD. The younger sibling was diagnosed and treated with folinic acid at an early‐symptomatic stage. Both patients had moderately low age‐related CSF 5‐methyltetrahydrofolate levels at diagnosis with the older sibling (that was already treated at base line collection) averaging 19 nmol/L (normal range: 44‐122 nmol/L) and the younger one 49 nmol/L (normal range 63‐122 nmol/L). These levels were restored to normal limits after folinic supplementation.