X inactivation :
the phenomenon in a female by which one X chromosome (either the maternally or paternally derived X) is randomly (by chance) inactivated in an early embryonic cell, with fixed inactivation of that same X in all cells descended from that cell. The change that occurs with X inactivation is epigenetic : it is a heritable change in gene function without a change in the sequence of the DNA.
X inactivation is not restricted to females. It also occurs in males with Klinefelter syndrome who have more than one X chromosome.
Uniparental disomy :
describes the abnormal assortment of chromosomes from parent to child. Normally, one-half of the genetic material is derived from each parent. In uniparental disomy, the chromosome number is correct, but both members of a chromosome pair or segments of a chromosome pair are inherited from the same parent. The detection of uniparental disomy involves PCR analysis of genetic material from the affected child and both parents. Genetic conditions that are often associated with uniparental disomy include Prader-Willi syndrome, Angelman syndrome, Russell-Silver syndrome and various other malformation syndromes.
Genomic imprinting on chromosome 15 due to the deletion 15q11q13 results in two disparate syndromes:
Loss of a parental region may be due to either physical deletion or uniparental disomy. Uniparental disomy arises when both copies (alleles) of a gene or chromosome are inherited from the same parent, which can result in either identical alleles (isodisomy) or different alleles (heterodisomy).
All of this examples have a normal cariotype (46,XX or 46,XY) only the Fish analysis could show the deletion.
Pegoraro e Avoyer
