SLC16A2 and tyrosine hydroxylase deficiency: Alternatively, the well-described endocrine alterations after global loss of MCT8, such as high serum T3 and low serum T4 levels and/or impaired transport of T3 across the BBB, which in turn causes a mild central TH deficiency (Ceballos et al., 2009, Trajkovic et al., 2007), may impact NB differentiation and GCN formation.