Chromosome fragility and psychopathology in obligate female carriers of the fragile X chromosome.

The relationship between fragility (the percentage of cells exhibiting the fragile X chromosome abnormality) and psychopathological conditions was investigated in a sample of 40 obligate female carriers of the fragile X chromosome. Subjects were categorized by those with positive fragility greater than 0% (n = 19) and those with 0% fragility (n = 21). Compared with women with 0% fragility, it was expected that women with positive fragility would have a higher likelihood of manifesting a spectrum of social and psychological disability previously shown to be associated with fragile X syndrome in women. It was also expected that within the group with positive fragility, degree of fragility would be related to severity of symptoms. Results partially supported the hypotheses: women with fragility over 0% were more likely to be assigned a diagnosis of schizotypal features, were rated higher on symptoms associated with the schizophrenia spectrum, and scored lower on IQ, level of healthiest functioning, education, and socioeconomic status than women with 0% fragility. Subsequent comparisons with a control group indicated that the group with 0% fragility and normal controls did not differ on these variables. Within the group with positive fragility, increasing fragility was related to greater severity of symptoms and lower IQ, education, socioeconomic status, and levels of adaptive functioning, as predicted. Contrary to expectations, positive fragility was not associated with proportion of affective disorder diagnoses or ratings on affective disorder symptoms. The results of the study provide evidence that degree of fragility is a potentially important predictor of psychopathology among women with normal IQ who are carriers of the fragile X chromosome abnormality.