Allelic imbalance at 13q31 is associated with reduced GPC6 in Chinese with sporadic retinoblastoma.
OBJECTIVE
Loss of heterozygosity (LOH) has been discovered in retinoblastoma (RB) in previous studies. In this study, we aimed to discover potential tumour suppressor genes through investigation of the incidence of allelic loss in chromosome 1, 6, 9, 13, 19, 20, 21, 22 and X in Chinese sporadic retinoblastoma patients and to study the expression of genes flanking LOH region 13q31.


METHODS
Twenty-five microdissected RB samples were analysed to investigate the LOH in 140 microsatellite markers. Expression of genes flanking D13S265 was investigated by real-time quantitative-PCR on available frozen samples. The promoter and entire coding region of GPC6 were examined for sequence changes in an extended batch of 29 RB samples.


RESULTS
Allele losses were found in 92% (23/25) of the tumours. We identified a new LOH locus at 13q31 (D13S265) with a high occurrence rate (67%, 14/21) apart from the RB1 locus (68%, 17/25). Expression study detected the reduced expression of Glypican 6 (GPC6) transcript significantly associated with the LOH at 13q31 (p=0.024). Furthermore, mutation screening revealed no remarkable sequence alteration in GPC6 that could affect its expression.


CONCLUSIONS
Results suggest that a reduction in GPC6 mRNA in retinoblastoma is associated with the non-random allelic loss at 13q31 that could contribute to RB development.
Lau
Charles S L
CS
Department of Ophthalmology & Visual Sciences, The Chinese University of Hong Kong, Shatin, Hong Kong SAR.
Yu
Christopher B O
CB
Wong
H K
HK
Fan
Dorothy S P
DS
Mak
H T
HT
Wong
K W
KW
Lam
Dennis S C
DS
Pang
Chi Pui
CP
Choy
Kwong Wai
KW
D002675:Child, Preschool; D002874:Chromosome Mapping; D002882:Chromosomes, Human, Pair 13 / Q000235:genetics*; D004252:DNA Mutational Analysis / Q000379:methods; D015870:Gene Expression; D053673:Glypicans / Q000096:biosynthesis* / Q000235:genetics; D006801:Humans; D007223:Infant; D019656:Loss of Heterozygosity; D042282:Microdissection / Q000379:methods; D018895:Microsatellite Repeats; D009363:Neoplasm Proteins / Q000378:metabolism; D011379:Prognosis; D012333:RNA, Messenger / Q000235:genetics; D012334:RNA, Neoplasm / Q000235:genetics; D019572:Retinal Neoplasms / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D012175:Retinoblastoma / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D014407:Tumor Cells, Cultured
C120300:GPC6 protein, human; D053673:Glypicans; D009363:Neoplasm Proteins; D012333:RNA, Messenger; D012334:RNA, Neoplasm