A novel large deletion of the ICR1 region including H19 and putative enhancer elements.
BACKGROUND
Beckwith-Wiedemann syndrome (BWS) is a rare pediatric overgrowth disorder with a variable clinical phenotype caused by deregulation affecting imprinted genes in the chromosomal region 11p15. Alterations of the imprinting control region 1 (ICR1) at the IGF2/H19 locus resulting in biallelic expression of IGF2 and biallelic silencing of H19 account for approximately 10% of patients with BWS. The majority of these patients have epimutations of the ICR1 without detectable DNA sequence changes. Only a few patients were found to have deletions. Most of these deletions are small affecting different parts of the ICR1 differentially methylated region (ICR1-DMR) removing target sequences for CTCF. Only a very few deletions reported so far include the H19 gene in addition to the CTCF binding sites. None of these deletions include IGF2.


METHODS
A male patient was born with hypotonia, facial dysmorphisms and hypoglycemia suggestive of Beckwith-Wiedemann syndrome. Using methylation-specific (MS)-MLPA (Multiplex ligation-dependent probe amplification) we have identified a maternally inherited large deletion of the ICR1 region in a patient and his mother. The deletion results in a variable clinical expression with a classical BWS in the mother and a more severe presentation of BWS in her son. By genome-wide SNP array analysis the deletion was found to span ~100 kb genomic DNA including the ICR1DMR, H19, two adjacent non-imprinted genes and two of three predicted enhancer elements downstream to H19. Methylation analysis by deep bisulfite next generation sequencing revealed hypermethylation of the maternal allele at the IGF2 locus in both, mother and child, although IGF2 is not affected by the deletion.


CONCLUSIONS
We here report on a novel large familial deletion of the ICR1 region in a BWS family. Due to the deletion of the ICR1-DMR CTCF binding cannot take place and the residual enhancer elements have access to the IGF2 promoters. The aberrant methylation (hypermethylation) of the maternal IGF2 allele in both affected family members may reflect the active state of the normally silenced maternal IGF2 copy and can be a consequence of the deletion. The deletion results in a variable clinical phenotype and expression.
Aghia Sophia Children's Hospital, University of Athens Medical School, Athens, Goudi, 11527, Greece. efrysira@yahoo.gr.
Helen
H
Fryssira
Mitera Maternity Hospital, Athens, Greece. amenta@hol.gr.
Stella
S
Amenta
Institute of Human Genetics, University Hospital Essen, University Duisburg-Essen, Essen, Germany. deniz.kanber@uni-due.de.
Deniz
D
Kanber
Aghia Sophia Children's Hospital, University of Athens Medical School, Athens, Goudi, 11527, Greece. csofokl@med.uoa.gr.
Christalena
C
Sofocleous
First Pediatric Clinic, Aghia Sophia" Children's Hospital, University of Athens School of Medicine, Athens, Greece. lilialykopoulou@gmail.com.
Evangelia
E
Lykopoulou
First Pediatric Clinic, Aghia Sophia" Children's Hospital, University of Athens School of Medicine, Athens, Greece. c.kanaka-gantenbein@med.uoa.gr.
Christina
C
Kanaka-Gantenbein
Institute of Genetics and Biophysics A. Buzzati-Traverso, CNR, DiSTABiF, 2nd University of Naples, Naples, Italy. flavia.cerrato@unima2.it.
Flavia
F
Cerrato
Institute of Human Genetics, University Hospital Essen, University Duisburg-Essen, Essen, Germany. Hermann-josef.luedecke@uni-due.de.
Hermann-Josef
HJ
Lüdecke
Institute of Human Genetics, University Hospital Schleswig-Hostein Campus Kiel/Christian-Albrechts University Kiel, Kiel, Germany. sbens@medgen.uni-kiel.de.
Susanne
S
Bens
Institute of Genetics and Biophysics A. Buzzati-Traverso, CNR, DiSTABiF, 2nd University of Naples, Naples, Italy. andrea.riccio@unima2.it.
Andrea
A
Riccio
Institute of Human Genetics, University Hospital Essen, University Duisburg-Essen, Essen, Germany. Karin.buiting@uni-due.de.
Karin
K
Buiting
D000328:Adult; D001506:Beckwith-Wiedemann Syndrome / Q000235:genetics*; D020732:Cytogenetic Analysis; D019175:DNA Methylation; D004742:Enhancer Elements, Genetic / Q000235:genetics*; D005260:Female; D056426:Genetic Loci / Q000235:genetics*; D006801:Humans; D007231:Infant, Newborn; D007335:Insulin-Like Growth Factor II / Q000235:genetics; D008297:Male; D010641:Phenotype; D011247:Pregnancy; D017384:Sequence Deletion
C035170:IGF2 protein, human; D007335:Insulin-Like Growth Factor II