Although cognitive impairment and developmental delay are the hallmarks of human Cr deficiency syndromes, muscular hypotonia and myopathy were also described in patients with AGAT, GAMT, and CT1 deficiency (Stockler et al., 1996; Anselm et al., 2006; Nouioua et al., 2013). Here, SLC6A8 is linked to Global developmental delay.