Dynamic mosaicism manifesting as loss, gain and rearrangement of an isodicentric Y chromosome in a male child with growth retardation and abnormal external genitalia.

Isodicentric chromosomes are considered the most common structural abnormality of the human Y chromosome. Because of their instability during cell division, loss of an isodicentric Y seems mainly to lie at the origin of mosaicism in previously reported patients with a 45,X cell line. Here, we report on a similar case, which, however, turned out to be an example of dynamic mosaicism involving isodicentric chromosome Y and isochromosome Y after FISH with a set of chromosome Y-specific probes and multicolor banding. Cytogenetic analyses (GTG-, C-, and Q-banding) have shown three different cell lines: 45,X/46, X,idic(Y)(q12)/46,X,+mar. The application of molecular cytogenetic techniques established the presence of four cell lines: 45,X (48%), 46,X,idic(Y)(q11.23) (42%), 46,X,i(Y)(p10) (6%) and 47,X,idic(Y)(q11.23),+idic(Y)(q11.23) (4%). According to the available literature, this is the first case of dynamic mosaicism with up to four different cell lines involving loss, gain, and rearrangement of an idic(Y)(q11.23). The present report indicates that cases of mosaicism involving isodicentric and isochromosome Ys can be more dynamic in terms of somatic intercellular variability that probably has an underappreciated effect on the phenotype.