The role of EXT1 in nonhereditary osteochondroma: identification of homozygous deletions.
BACKGROUND
Multiple osteochondromas is a hereditary syndrome that is characterized by the formation of cartilage-capped bony neoplasms (osteochondromas), for which exostosis (multiple)-1 (EXT1) has been identified as a causative gene. However, 85% of all osteochondromas present as solitary (nonhereditary) lesions in which somatic mutations in EXT1 are extremely rare, but loss of heterozygosity and clonal rearrangement of 8q24 (the chromosomal locus of EXT1) are common. We examined whether EXT1 might act as a classical tumor suppressor gene for nonhereditary osteochondromas.


METHODS
Eight nonhereditary osteochondromas were subjected to high-resolution array-based comparative genomic hybridization (array-CGH) analysis for chromosome 8q. The array-CGH results were validated by subjecting tumor DNA to multiple ligation-dependent probe amplification (MLPA) analysis for EXT1. EXT1 locus-specific fluorescent in situ hybridization (FISH) was performed on nuclei isolated from the three tissue components of osteochondroma (cartilage cap, perichondrium, bony stalk) to examine which parts of the tumor are of clonal origin.


RESULTS
Array-CGH analysis of tumor DNA revealed that all eight osteochondromas had a large deletion of 8q; five tumors had an additional small deletion of the other allele of 8q that contained the EXT1 gene. MLPA analysis of tumor DNA confirmed these findings and identified two additional deletions that were smaller than the limit of resolution of array-CGH. FISH analysis of the cartilage cap, perichondrium, and bony stalk showed that these homozygous EXT1 deletions were present only in the cartilage cap of osteochondroma.


CONCLUSIONS
EXT1 functions as a classical tumor suppressor gene in the cartilage cap of nonhereditary osteochondromas.
Hameetman
Liesbeth
L
Department of Pathology, Leiden University Medical Center, PO Box 9600 L1-Q, 2300 RC Leiden, The Netherlands.
Szuhai
Karoly
K
Yavas
Ayse
A
Knijnenburg
Jeroen
J
van Duin
Mark
M
van Dekken
Herman
H
Taminiau
Antonie H M
AH
Cleton-Jansen
Anne-Marie
AM
Bovée
Judith V M G
JV
Hogendoorn
Pancras C W
PC
D002898:Chromosomes, Human, Pair 8; D004273:DNA, Neoplasm / Q000032:analysis; D017353:Gene Deletion; D015972:Gene Expression Regulation, Neoplastic; D016147:Genes, Tumor Suppressor; D006132:Growth Plate / Q000378:metabolism / Q000473:pathology; D006720:Homozygote; D006801:Humans; D017404:In Situ Hybridization, Fluorescence; D017351:N-Acetylglucosaminyltransferases / Q000235:genetics*; D015831:Osteochondroma / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D012333:RNA, Messenger / Q000032:analysis; D012334:RNA, Neoplasm / Q000032:analysis; D020133:Reverse Transcriptase Polymerase Chain Reaction; D000099058:Exostosin 1
D004273:DNA, Neoplasm; D012333:RNA, Messenger; D012334:RNA, Neoplasm; D017351:N-Acetylglucosaminyltransferases; D000099058:Exostosin 1