Clinical Guidance
SLC19A1 encodes the reduced folate carrier (RFC) protein that mediates transport of folates into mammalian cells. The clinical findings associated with SLC19A1-related folate transport deficiency (SLC19A1-FTD) depend on the degree of RFC functional loss associated with the pathogenic variants . With severe deficiency, signs may be present at or shortly after birth . With modest loss of function, clinical manifestations may be delayed and only emerge when dietary folate intake is insufficient . When the sole manifestations are hematologic, immunologic/infectious, and/or gastrointestinal, treatment with folate can completely reverse these signs and symptoms. Developmental and neurologic findings may improve with treatment depending on the extent and duration of impairment and adequacy of treatment (see Management, ). To date, five individuals from three families have been identified with biallelic pathogenic variants in SLC19A1 . In addition, two sibs died at an early age prior to diagnosis . The following description of the phenotypic features associated with this condition in untreated individuals is based on these reports. Table 2. SLC19A1-Related Folate Transport Deficiency: Frequency of Select Features in Untreated Individuals
