Thus, the structural aberrations of sugar transferase genes in BPAD and schizophrenia and the recent findings that the germ line homozygous mutations of ALG9 leads to progressive microcephaly, cerebral and cerebellar atrophy underscores the significance of N-glycosylation pathway in central nervous system homeostasis and may warrant further analyses of ALG9 and other mannosyltransferase genes in the etiopathogenesis of psychosis. Here, ALG9 is linked to microcephaly.