OP6 – 2631: Decreased free-thiamine in cerebro spinal fluid and fibroblasts is a sensitive marker of thiamine transporter 2 deficiency in Leigh syndrome patients

Objectives Thiamine transporter-2 (hTHTR2) deficiency due to SLC19A3 mutations is a potentially reversible cause of Leigh syndrome for which no biochemical markers are currently available. Our aim was to assess the sensitivity of thiamine quantification in cerebrospinal fluid (CSF) and fibroblasts from patients with Leigh encephalopathy and SLC19A3 defects as compared with other causes of Leigh syndrome. Methods Thiamine vitamers (free-thiamine, thiamine monophosphate (TMP) and thiamine diphosphate (TDP)) were analyzed by HPLC-fluorescence detection in whole-blood and cerebrospinal fluid (CSF) samples from 106 and 38 paediatric controls, respectively. Results were compared with patients with Leigh syndrome due to SLC19A3 defects (N=6) and mitochondrial respiratory chain defects (N=9). In all but one SLC19A3 patient, samples were collected before thiamine supplementation. Thiamine vitamers were also analyzed by HPLC in fibroblasts from SLC19A3 patients (N=3) and patients with other metabolic defects (N=6). Results A negative correlation between thiamine isoforms and age was detected in whole-blood and CSF, thus three reference intervals were established for free-thiamine and two intervals for TMP and TDP. Free-thiamine was severely reduced in five non-treated SLC19A3 patients CSF, but not TMP and TPP. The SLC19A3 patient under thiamine supplementation showed thiamine values above reference range. Nine Leigh patients with mitochondrial defects showed normal o slightly reduced values for CSF thiamine. In SLC19A3 patient's fibroblasts, a reduction in free-thiamine was detected as compared with control sample. These values normalized after thiamine was added to the culture medium. Conclusion SLC19A3 patients show a profound deficiency of free-thiamine in the CSF that allows their identification from other causes of Leigh syndrome. SLC19A3 is essential to maintain CSF thiamine homeostasis and to prevent brain damage. Thiamine overload can supply the SLC19A3 defect and restore thiamine values in fibroblasts and CSF, probably by an alternative transport system.