Unravelling the parental origin and mechanism of formation of the 47,XY,i(X)(q10) Klinefelter karyotype variant.

OBJECTIVE: To describe the parental origin and the mechanism of formation of an 47,XY,idic(X)(p11.2) karyotype in a patient with Klinefelter syndrome.
DESIGN: Case report.
SETTING: A university hospital. PATIENT(S): A 36-year-old man with primary infertility. INTERVENTION(S): Genotype-phenotype correlation and microsatellite marker-mediated haplotype analysis subsequent to whole genome amplification of microdissected chromosomes. MAIN OUTCOME MEASURE(S): Genotype-phenotype correlation, mechanism of formation, and parental origin. RESULT(S): Maternal origin of the isochromosome and the normal X chromosome and loss of maternal heterozygosity for all informative Xq markers on the isochromosome and in each case, the presence of the other maternal allele on the normal homologue was shown. Comparative analysis of the clinical features of 17 additional cases and of 1 case with a 46,XY/47,XY,i(X)(q10) karyotype reported in the literature revealed a phenotype very similar to the clinical findings in patients with a 47,XXY karyotype. CONCLUSION(S): The molecular results in our patient indicate a maternal origin of a true dicentric isochromosome and most likely postzygotic formation subsequent to a nondisjunction in maternal meiosis II. With the exception of the final height the phenotype of Klinefelter syndrome appears not to be the consequence of trisomy of the pseudoautosomal region on Xp.