Constitutional chromosomal breakage

Abstract

There were 18 individuals found to have a constitutional chromosome fragility causing an increase in break frequency. For each chromosome the breakpoint is always the same, whether it involves chromosomes from the same person, the same family, or different families. The fragile points are bands 10q24, 12q13, 16q21, 17p12, and Xq27. Autosomal constitutional fragility does not seem to have a phenotypic correspondence. They were found mostly in parents of children with chromosomal abnormalities or in couples with a history of repeated spontaneous abortions which permits one to raise the possibility of an interchromosomal effect. The six constitutional chromosomal fragilities of the X chromosome had in common the association of mental deficiency, delayed speech, and large malformed ears. The break points in constitutional chromosomal fragility were compared to those of spontaneous breaks in vitro, to those induced by X-rays, and to those in Fanconi's anemia. The theoretical consequences of these structural abnormalities are discussed as well as what to do about them when they are found.

Distribution of spontaneous chromosome breaks in man

“…1969;Buhi.ir et al, 1970;Kun/.i -Muhl et al. 1970;Magenis et al, 1970;Raoul, 1970;Dlminatti et al, 1971;Fraccaro et al, 1971;F lrguson-Sm iih , 1973;G iraud et al. 1976).…”

An Opportune Life: 50 Years in Human Cytogenetics

“…While I was immersed in the study of spontaneous abortions, along came another exciting cytogenetic phenomenon: the observation of a cytogenetically demonstrable marker on the X chromosome associated with a common form of X-linked mental retardation (13,15). The cytogenetic marker came to be called a fragile site, and it was the study of fragile X-linked mental retardation that led to the recognition of an entirely novel type of mutation, trinucleotide repeat expansions.…”

The rare human fragile site 16B

“…Spontaneous FRA16B was first localized in band 16q21 by Giraud et al (1976) using R-banding. Later, (Magenis and Chamberlin, 1979) mapped FRA16B to 16q22.00 using Gbands.…”