AP4B1 and AP-4 deficiency syndrome: Several of these observations correlate well with symptoms seen in patients suffering from SPG47 and other AP-4 deficiency syndromes.6,7,35-38 Deficit in rotarod performance has also been observed in two separately published murine models of AP-4 deficiency.13,14 In contrast, the observation of increased ambulation in the open-field test seen in the AP-4 deficient mice does not appear to have a cognate symptom in human patients.