Importance of Immediate Thiamine Therapy in Children with Suspected Thiamine-Responsive Megaloblastic Anemia—Report on Two Patients Carrying a Novel SLC19A2 Gene Mutation

Thiamine-responsive megaloblastic anemia (TRMA) is an autosomal recessive disorder characterized by the development of megaloblastic anemia, diabetes mellitus, and sensorineural deafness. We report on the first two Croatian patients with TRMA, compound heterozygotes for nonsense, c.373C > T; p.(Gln125Ter) and novel missense variant, c.1214C > G; p.(Thr405Arg) in SLC19A2 gene. The first was diagnosed at 4 months with diabetes mellitus and severe anemia requiring transfusions. As TRMA was suspected, thiamine therapy was immediately started to prevent further transfusions and insulin therapy. His brother developed extreme anemia at 3 weeks of age while waiting for the results of the genetic test. Severe anemia in this sibling may have been prevented if thiamine had been initiated earlier.

A Novel Mutation of SLC19A2 in a Chinese Zhuang Ethnic Family with Thiamine-Responsive Megaloblastic Anemia

Background/Aims: Thiamine-responsive megaloblastic anemia syndrome is a rare autosomal recessive disorder resulting from mutations in SLC19A2, and is mainly characterized by megaloblastic anemia, diabetes, and progressive sensorineural hearing loss. Methods: We study a Chinese Zhuang ethnicity family with thiamine-responsive megaloblastic anemia. The proband of the study presented with anemia and diabetes, similar to his late brother, as well as visual impairment. All clinical manifestations were corrected with thiamine (30 mg/d) supplementation for 1–3 months, except for visual impairment, which was irreversible. The presence of mutations in all exons and the flanking sequences of the SLC19A2 gene were analyzed in this family based on the proband’s and his brother’s clinical data. Computer analysis and prediction of the protein conformation of mutant THTR-1. The relative concentration of thiamine pyrophosphate in the proband’s whole blood before and after initiation of thiamine supplement was measured by high performance liquid chromatography (HPLC). Results: Gene sequencing showed a homozygous mutation in exon 6 of the SLC19A2 gene (c.1409insT) in the proband. His parents and sister were diagnosed as heterozygous carriers of the c.1409insT mutation. Computer simulation showed that the mutations caused a change in protein conformation. HPLC results suggested that the relative concentration of thiamine pyrophosphate in the proband’s whole blood after thiamine supplement was significantly different (P=0.016) from that at baseline. Conclusions: This novel homozygous mutation (c.1409insT) caused the onset of thiamine-responsive megaloblastic anemia in the proband.