Microduplications upstream of MSX2 are associated with a phenocopy of cleidocranial dysplasia.
BACKGROUND
Cleidocranial dysplasia (CCD) is an autosomal dominant skeletal disorder characterised by hypoplastic or absent clavicles, increased head circumference, large fontanels, dental anomalies and short stature. Although CCD is usually caused by mutations leading to haploinsufficiency of RUNX2, the underlying genetic cause remains unresolved in about 25% of cases.


METHODS
Array comparative genomic hybridisation was performed to detect copy number variations (CNVs). Identified CNVs were characterised by quantitative PCR and sequencing analyses. The effect of candidate genes on mineralisation was evaluated using viral overexpression in chicken cells.


RESULTS
In 2 out of 16 cases, the authors identified microduplications upstream of MSX2 on chromosome 5q35.2. One of the unrelated affected individuals presented with a phenocopy of CCD. In addition to a classical CCD phenotype, the other subject had a complex synpolydactyly of the hands and postaxial polydactyly of the feet which have so far never been reported in association with CCD or CNVs on 5q35.2. The duplications overlap in an ∼219 kb region that contains several highly conserved non-coding elements which are likely to be involved in MSX2 gene regulation. Functional analyses demonstrated that the inhibitory effect of Msx2 overexpression on mineralisation cannot be ameliorated by forced Runx2 expression.


CONCLUSIONS
These results indicate that CNVs in non-coding regions can cause developmental defects, and that the resulting phenotype can be distinct from those caused by point mutations within the corresponding gene. Taken together, these findings reveal an additional mechanism for the pathogenesis of CCD, particularly with regard to the regulation of MSX2.
Institute for Medical Genetics and Human Genetics, Charité-Universitätsmedizin Berlin, Berlin, Germany.
Claus Eric
CE
Ott
Hendrikje
H
Hein
Silke
S
Lohan
Jeannette
J
Hoogeboom
Nicola
N
Foulds
Johannes
J
Grünhagen
Sigmar
S
Stricker
Pablo
P
Villavicencio-Lorini
Eva
E
Klopocki
Stefan
S
Mundlos
D000818:Animals; D002478:Cells, Cultured; D002645:Chickens; D002648:Child; D002675:Child, Preschool; D058674:Chromosome Duplication; D002895:Chromosomes, Human, Pair 5 / Q000235:genetics; D002973:Cleidocranial Dysplasia / Q000235:genetics* / Q000378:metabolism; D050659:Core Binding Factor Alpha 1 Subunit / Q000235:genetics / Q000378:metabolism; D056915:DNA Copy Number Variations; D005260:Female; D005786:Gene Expression Regulation; D057895:Haploinsufficiency; D006579:Heterozygote; D018398:Homeodomain Proteins / Q000235:genetics* / Q000378:metabolism; D006801:Humans; D008297:Male; D020411:Oligonucleotide Array Sequence Analysis; D010641:Phenotype; D017354:Point Mutation; D016133:Polymerase Chain Reaction; D020641:Polymorphism, Single Nucleotide; D017422:Sequence Analysis, DNA
D050659:Core Binding Factor Alpha 1 Subunit; D018398:Homeodomain Proteins; C084119:MSX2 protein; C493709:RUNX2 protein, human