The fibroblast growth factor 21 concentration in children with mitochondrial disease does not depend on the disease stage, but rather on the disease genotype

Abstract
The fibroblast growth factor 21 (FGF21) is a new biomarker of mitochondrial diseases (MD). FGF21 concentration may be used to define the severity of mitochondrial disease.

Aim of the study
The study objective was to verify if the FGF21 concentration in paediatric patients with MD was correlated with the disease severity and stage and to assess the correlation between FGF21 levels and the genetic background of MD.

Material and methods
The disease stage in MD subjects was determined on the basis of the International Paediatric Mitochondrial Disease Scale (IPMDS) and the concentrations of FGF21, lactic and pyruvic acids, alanine and creatine kinase in serum were assessed in those patients.

Results
The median age of children with MD (n = 32) was 33 months (range: 2–213), in the control group (n = 21) the median age was 42 months (range: 8–202). The concentrations of FGF21, lactic acid and pyruvic acid were higher in MD patients than in the control group. No correlation between the disease severity (IPMDS) and serum FGF21 concentration was found. The FGF21 concentration was higher in patients whose MD resulted from nuclear gene damage (nDNA), median FGF21 = 1022 (84–8873) pg/ml, than in patients with MD resulting from mitochondrial damage (mtDNA), median FGF21 = 736 (188–2906) pg/ml, or with an abnormal variant in the PDHA1 gene, median FGF21 = 58 (25–637) pg/ml.

Conclusions
There is no correlation between the stage of MD and FGF21 level. Higher FGF21 values are seen in patients whose MD results from an abnormal nDNA variant rather than mtDNA damage.