Karyotype-phenotype correlation in females with X chromosome abnormalities

In mammals, females have a pair of X chromosomes, whereas males have one X chromosome and one Y chromosome, which is much smaller and contains fewer genes than a X chromosome. One of the pair of X chromosomes is inactivated in females. The inactivated X chromosome is late-replicating, heterochromatic, and genetically unexpressed. An X inactivation center (XIC) located at a proximal region on Xq is thought to control inactivation of an X chromosome. There has been increasing scientific interest in the relationship between chromosomal and clinical findings in different chromosomal aberrations, whether affecting the sex chromosomes or the autosomes. The genetic and molecular implications of the karyotype/phenotype controversy have recently been considered with the aim of better understanding the interplay of specific genes carried on different chromosomes in organ development and differentiation. Karyotype/phenotype correlation showed the gradation of severity of clinical phenotype to be related to the number of X chromosomes.