A 46,XYq 8-year-old male was referred for microcephaly, growth, and mental retardation, hypotonia, genital hypoplasia, and dysmorphisms. FISH analysis showed that the rearranged Y chromosome originated from an unbalanced translocation of Xq27.3-qter onto the deleted Yq11.22. Analysis of reported patients with disomy of region distal to Xq26 suggests that this rare anomaly, associated with failure to dosage compensate X-linked genes that are normally inactivated, when present in two copies, is causing a quite distinct phenotype. This imbalance is the aberrant by product of the recombinogenic pairing of the distal pseudoautosomal Xq-Yq region at male meiosis.
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