The human brain contains about 10¹² neurons, each forming as many as 1,000 connections with other neurons [1]. The brain also contains an enormous amount of glial (neuroglial) cells, which occupy the spaces between neu­rons and modulate their functions. Indirect evidences for some forms of somatic genomic and chromosomal alter­ations have been obtained [2]. Precedent exists for aneu­ploidies during early mammalian development which were thought to result in cell death [3,4]. Visualization of meta­phase chromosomes by a nuclear transfer technique in mouse cortical neurons has indicated that the majority of them have an abnormal karyotype [5]. Direct fluorescent in situ hybridization (FISH) and spectral karyotype analy­sis of neurons in the developing and adult nervous system of mouse embryonic cerebral cortical neuroblasts have been performed, and have identified more than 30% of neuroblasts to be aneuploid [2]. Therefore, it is possible that genomes in developing and adult neurons can be dif­ferent at the level of whole chromosomes. However, up-to-date studies of interphase chromosome complement in non dividing neuronal cells in the human fetal brain have not been carried out.