Van Roy B C, Willems P J, Vits L J, Ceulemans B P, Coucke P J, Van der Auwera B J, Lormans J A, Dumon J E
Department of Medical Genetics, University of Antwerp-UIA, Wilrijk, Belgium.
Am J Med Genet. 1990 May;36(1):122-5. doi: 10.1002/ajmg.1320360124.
We describe two male sibs with mental retardation discordant for the fragile-X syndrome. In the younger sib, chromosome analysis under folate deprivation showed a fragile site at Xq27.3 in 12-46% of mitoses. In the older sib, however, repeated chromosome analyses (six different cultures with analysis of 50 mitoses each) under identical conditions could not detect any fragile-X site. Using DNA probes linked to the fragile-X gene, we found evidence that the two sibs inherited a different maternal X chromosome at Xq27.3. This excluded the presence of the fragile-X syndrome in the older sib with a probability of greater than 99%.
