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Cytogenetic and molecular study of a jumping translocation in a baby with Dandy-Walker malformation

Editor—Jumping translocations are rare chromosomal events in which a donor chromosome segment is translocated to various recipient chromosome sites. Jumping translocations were initially described in constitutional chromosome syndromes,1 ,2 but the majority of published cases have been observed in haematological malignancies, where their presence has been related to poor prognosis.3 ,4 

Most jumping translocations involve acrocentric chromosomes and a characteristic feature is that breakpoints usually concern areas of repetitive DNA (telomeric, centromeric, or heterochromatic regions). Recipient chromosome involvement seems to be randomly distributed but with a preferential involvement of telomeric segments. This has led to the hypothesis that repetitive telomeric sequences could be implicated in the occurrence of jumping translocations, as suggested by FISH studies which have reported the presence of interstitial telomeric sequences at the junction sites of jumping translocations.5 ,6 However, the molecular basis underlying these complex chromosomal rearrangements is not well understood.

Constitutional jumping translocations are extremely rare and are usually associated with various phenotypic abnormalities. We report the finding of a jumping translocation in a baby with Dandy-Walker malformation. Dandy-Walker malformation consists of the triad (1) hypoplasia or absence of the vermis, (2) upward displacement of the falx, lateral sinuses, and torcular, and (3) a large, thin walled retrocerebellar cyst formed by the roof of the fourth ventricle. Most Dandy-Walker malformations are sporadic. The Possum database reports six autosomal dominant syndromes and 37 autosomal recessive syndromes which can be associated with Dandy-Walker malformation. However, in these disorders, Dandy-Walker malformation is always one feature of a larger spectrum of anomalies. Various cytogenetic abnormalities have been reported, but to date no consistent chromosomal aberration has been recognised.7 ,8 The present study combines molecular and cytogenetic investigations, including FISH and PRINS labelling procedures, to characterise a constitutional jumping translocation. …