TH and Allan-Herndon-Dudley syndrome: So important is the role of these neurons in the motor system that any alteration in them, such as lack of trophism and/or defects in synaptic plasticity caused by TH deficiency due to missing transporter(s), produces the typical symptoms of upper motor neuron disease, which is present in AHDS patients as bilateral Babinski reflexes and hyperreflexia [90] and in the patient with OATP1C1 deficiency as spasticity of the lower limbs [24].