Reproductive outcome in 3 families with a satellited chromosome 4 with review of the literature

Abstract

We describe 3 families segregating for a translocation of the nucleolus organizer region (NOR) onto chromosome 4. Review of previously reported cases of translocations involving NOR and chromosome 4 shows that these translocations may be associated with variable reproductive outcomes. We provide evidence that imprinting is not the mechanism responsible for the variable reproductive outcomes in the case of satellited 4p chromosomes; this may offer indirect support for a ribosomal gene position effect. Translocated ribosomal genes may influence the expression of neighboring genes and could explain the variable phenotypes in individuals with satellited nonacrocentric chromosomes. We recommend that prenatal counseling of individuals with satellited nonacrocentric chromosomes should be cautious.

Breakpoint within the nucleolus organizer region resulting in a reciprocal translocation t(4;14)(q21;p12)

“…More frequent are translocations of NORs to a terminal region of another chromosome resulting in a satellited nonacrocentric chromosome. In this scenario, the terminal 4q is the most affected region on an autosome [Arn et al, 1995;Guttenbach et al, 1999;Miller et al, 1995]. This could indicate a special preference of the terminal 4q to recombine with the short arms of acrocentric chromosomes.…”

“…Among these, NOR displacements dominate translocations of the whole NOR and an acrocentric chromosome short arm to a terminal region of another chromosome. These events result in satellited nonacrocentric chromosomes [for a review see Arn et al, 1995]. Less common are interstitial insertions of NORs into nonacrocentric chromosomes [Guttenbach et al, 1998[Guttenbach et al, , 1999Prieto et al, 1989;Watt et al, 1984].…”

Mosaicism for an ectopic NOR at 8pter and a complex rearrangement of chromosome 8 in a patient with severe psychomotor retardation

“…Ectopic NORs are rare findings in humans, but have been identified on chromosomes 1 through 5, 8, 9, 10, 12, 17, and 18 (Moore et al, 1992;Arn et al, 1995;Willatt et al, 2001). They arise from terminal translocations between acrocentric and non-acrocentric chromosomes and generally represent harmless chromosomal variations.…”

An interstitial nucleolus organizer region in the long arm of human chromosome 7: cytogenetic characterization and familial segregation

“…Up to now 30 mostly familial cases of Yqs (reviewed in Schmid et al, 1984 andCouturier-Turpin et al, 1994;Verma et al, 1997) and one case of Yps (Lin et al, 1995) have been described. Autosomes appear to be involved even less frequently, with most cases reported on satellited chromosomes 4 (reviewed in Arn et al, 1995).…”

“…As possible explanations imprinting of genes or influence of the translocated NOR on expression of neighboring genes have been suggested, of which the ribosomal gene position effect appears to be more likely (Arn et al, 1995).…”