Alterations of H19 imprinting and IGF2 replication timing are infrequent in Beckwith-Wiedemann syndrome

Beckwith-Wiedemann syndrome (BWS) is an over-growth disorder resulting from dysregulation of multiple imprinted genes through a variety of distinct me chanisms. A frequent alteration in BWS involves changes in the imprinting s tatus of the coordinately regulated IGF2 and H19 genes on 11p15. Patients h ave been categorized according to alterations in the imprinted expression, allele-specific methylation, and regional replication timing of these genes . In this work, IGF2/H19 expression, H19 DNA methylation, and IGF2 regional replication timing were studied in nine karyotypically normal BWS fibrobla sts and two BWS patients with maternally inherited 11p15 chromosomal rearra ngements. Informative patients (9/9) maintained normal monoallelic H19 expr ession/methylation, despite biallelic IGF2 expression in 6/9. Replication t iming studies revealed no changes in the pattern. of asynchronous replicati on timing for both a patient with biallelic IGF2 expression and a patient c arrying an 11p15 inversion. In contrast, a patient with a chromosome 11;22 translocation and normal H19 expression/methylation exhibited partial loss of asynchrony and a shift toward earlier replication times. These results i ndicate that in BWS, (1) H19 imprinting alterations are less frequent than previously estimated, (2) IGF2 imprinting and H19 imprinting are not necess arily coordinated, and (3) alterations in regional replication timing are g enerally not correlated with either chromosomal rearrangements or the impri nting status of IGF2 and H19. (C) 2000 Academic Press.