Traditionally the genus has been seen as a single species, Rhabdomys pumilio, though modern evidence on the basis of karyotype and mtDNA analysis suggests that it comprises two or more species and subspecies.
The first published report of a woman with a 47,XXX karyotype was by Patricia A. Jacobs, et al. at Western General Hospital in Edinburgh, Scotland, in 1959.
The first published report of a female with a 45,X karyotype was in 1959 by Dr. Charles Ford and colleagues in Harwell, Oxfordshire and Guy's Hospital in London.
Later research showed that the condition could manifest in patients with normal karyotypes, without duplication of the chromosomes, and the most recent genetic research implicates problems with the gene code FBXW11 as a likely cause.