We suggest that a diagnosis of TRMA should be considered in children with isolated diabetes presenting in the first year of life and that a normal Hb and/or MCV should not preclude genetic testing for mutations in SLC19A2. Interestingly, unlike type 1 diabetes, some participants in our cohort were incidentally found to have asymptomatic hyperglycaemia, indicating that some of these individuals may have a long period before diabetes symptoms appear. The gene discussed is GSTM1; the disease is thiamine-responsive megaloblastic anemia syndrome.