ASPM (asp (abnormal spindle) homolog, microcephaly associated)

The ASPM gene is the human equivalent of the Drosophila melanogaster 'abnormal spindle' gene (asp), which is known to be essential for normal mitotic spindle function in embryonic neuroblasts.  The mouse Aspm gene is also known to be expressed specifically in the  sites of prenatal cerebral cortical neurogenesis.  Inactivation of this gene in humans results in a severe condition called microcephaly, i.e. a small brain, associated with mental retardation. As human evolution is characterized by a dramatic increase in brain size, one group evaulated this gene and reported that it had undergone significantly higher rates of protein sequence evolution in primates than in rodents. Furthermore, they reported that ASPM has undergone even more rapid evolution in humans,  including evidence of a selective sweep in human populations. However, several aspects of these findings have been debated by other groups. Regardless, it is interesting that a gene that is associated with a small brain when it is damaged in humans, may have also shown increased evolution in humans.