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Objective: To provide current information on sex chromosome aneuploidies to obstetricians who encounter such diagnoses and who counsel prospective parents faced with the prenatal diagnosis of a sex chromosome aneuploidy. Data Sources: Unbiased information about the natural course of sex chromosome aneuploidy has become available only in the last few years. Current knowledge is based on seven prospective studies on unselected individuals with sex chromosome aneuploidy identified 20–30 years ago. All literature on sex chromosome aneuploidy was reviewed. Karyotypes specifically addressed included the following: 47,XXY, 47,XXX, 47,XYY, 45,X, 45,X/46,XX, 46,XX/47,XXX, and 46,XY/47,XXY. Methods of Study Selection: The international studies followed the affected subjects from birth to young adulthood. All published reports, case studies, and articles were reviewed. Tabulation, Integration, and Results: All prospective studies were included in the course of determining necessary information for obstetricians and prospective parents. Points addressed for each of the aneuploid karyotypes included expected phenotype, reproductive competence, developmental risks, and intervention therapies. Conclusion: Information about sex chromosome aneuploidy can assist obstetricians in providing accurate and comprehensive genetic counseling to parents of affected fetuses, and thereby facilitate the process of making an informed decision about pregnancy management.

Eleven unselected 47,XXX girls, now 15 to 22 years of age, have been observed from birth in a prospective study of children with sex chromosome anomalies. A description of their growth and development is presented. The 47,XXX infants were not generally distinguishable from chromosomally normal children in the first year of life, even though there was a slight delay in neuromotor development. By 2 years of age, developmental delays in speech and language often became evident, and speech therapy was often necessitated in the preschool years. Early school problems included speech and language deficiencies, lack of coordination, poor academic performance, and immature behavior; these persisted throughout the school years. By high school age, a 47,XXX girl was generally tall and often subject to somatic complaints. Sexual development was generally normal. Seven of the 11 propositae had a diagnosed psychiatric disorder or disturbance at some time during adolescence. Variability within this syndrome is great; one proposita is in college and another is mentally retarded. The frequency of the diagnosis of the 47,XXX karyotype by genetic amniocentesis is estimated to be 1/1000, the same incidence as in the newborn population. Expectant parents must be counseled as to the significance of this karyotype and prognostic information must be given. Suggested guidelines are included.