The first mutations identified in “microcephaly genes” are responsible for causing congenital, isolated, or primary microcephaly with recessive inheritance, and are termed microcephaly primary hereditary, or MCPH (MCPH1, OMIM # 251200 (MCPH1 [2]), MCPH2, OMIM # 604317 (WDR62 [3]), MCPH3, OMIM # 604804 (CDK5RAP2 [4,5]), MCPH4, OMIM # 604321 (CASC5 [5]) and MCPH5, OMIM #608716 (ASPM [6])). Here, KNL1 is linked to microcephaly.