Mutations in thiamine transporter, TDP synthesizing enzyme or carrier, including solute carrier family 19 member 3 (SLC19A3), thiamine pyrophosphokinase (TPK1) and solute carrier family 25 member 19 (SLC25A19), have been associated with developmental neurological disorders, including microcephaly and Leigh syndrome. This evidence concerns the gene TPK1 and microcephaly.