Complex but balanced chromosomal rearrangements can give rise, through recombination during meiosis, to complex unbalanced rearrangements. Here, we report on the case of a 21 months old child associating a 8q21.13 duplication and 8p23.3 microdeletion. The proposita was referred to our lab for cytogenetic exploration of a hydrocephalus associated with facial dysmorphism. He had also psychomotor retardation and microcephaly. The patient R-banding karyotype revealed a partial trisomy 8q captured by the p telomere of the same chromosome, whereas the parents’ karyotypes were normal. CGH-array technique characterized breakpoints and estimated its size to 61.8 Mb. Interestingly, an additional cryptic loss of 260 Kb in 8(p23.3-pter) was also identified by the same technique. These anomalies were confirmed by FISH technique.
The partial deletion of a chromosome arm in combination with partial duplication of the other was evocative of a recombinant chromosome deriving from a parental pericentric inversion. We suggest, therefore that a parental pericentric prezygotic 8(p23.3–q 21.13) inversion resulted in the complex unbalanced rearrangement of chromosome 8 in our patient. The clinical picture including hydrocephalus, inguinal hernia, long-term fever and psychomotor retardation, was described in patients with pure 8q2-qter duplication. However, the 8p23.3 microdeletion may contribute to the psychomotor retardation, microcephaly and some minor dysmorphic features. Here we emphasize the fact that the 8p microdeletion would be cytogenetically undetectable in the absence of CGH-array technique underlining the need of entire genome high-resolution analysis in patients with idiopathic mental retardation and/or birth defects even in abnormal conventional karyotype cases.
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