PSMB1 and Global developmental delay: In 2005, Eash et al. [1] reported a patient (Eash_1) with the smallest terminal deletion seen thus far, 390 kb, which only included the HI-genes TBP and PSMB1. This patient’s phenotype was comparable to the common terminal 6q deletion phenotype we describe and included microcephaly, brain abnormalities (corpus callosum abnormality, hydrocephaly), seizures, vertebral abnormalities, hypotonia and developmental delay (Tables 2, 3 and Additional file 3: Table S3; subgroup T-PSMB1).