Cytogenetics of Fragile X Chromosome: Autosomal Sites as Potential Markers for Fragile X Chromosome Analysis

Abstract

Fragile X chromosome screening was un- dertaken among 100 non-specific mentally retarded group from the Indian population. 14 subjects from 10 families showed the presence of fragile X chromosomes in 4 to 40% of cells. Various 'C' group autosomes showed the fragile sites at the telomeric regions of long arm in low percent- ages, which is well enough to be confused with fragile X chromosome manifestation in unbanded chromosome preparations. The necessity of analysing good G-banded preparations and scoring more number of cells for the con- firmation of fragile X syndrome cytogenetically has been stressed. The presence of constitutive fragile site at 3p14 and polymorphic 9qh+ in high percentages among fragile X positive subjects, made these markers a potential indi- cators in the diagnosis of fragile X syndrome. The impli- cations of the autosomal mimics and indicators in the dif- ferential diagnosis of fragile X syndrome has been high- lighted.