Temporal stability and age-related prevalence of loss of imprinting of the insulin-like growth factor-2 gene

Abstract

Background: Loss of genomic imprinting (LOI) of the insulin-like growth factor-2 gene (IGF2) is an epigenetic change involving abnormal activation of the normally silent maternally inherited allele. LOI of IGF2 gene is found in tumor tissue, normal adjoining mucosa and peripheral blood lymphocytes (PBL) of some patients with colorectal cancer (CRC), suggesting that this alteration precedes and is a risk factor for CRC. However, whether LOI of IGF2 is transitory or remains a permanent epigenetic alteration is unknown.

Results: Four-hundred patients, mean age 60.7 years (range 15-95), 287 (80%) Caucasian were studied. This included 210 (51.4%) patients with no colorectal neoplasia, and 190 (48.6) with colorectal neoplasia. LOI of IGF2 was present in all age strata examined, and no statistically significant association across age strata (p trend > 0.05) was noted. Forty-nine patients had repeat analysis of blood imprinting status at a mean follow up time of 38.2 +/- 12.9 months. All but three patients had the same imprinting status at follow up (94% agreement, kappa 0.79, p < 0.001). Genomic imprinting was stable for patients with and without colorectal neoplasia.

Methods: Standard RT-PCR assays for imprinting analysis of IGF2 were performed on PBL from ApaI informative individuals recruited at baseline and repeated 1 to 3 years later. Prevalence of LOI of IGF2 was also evaluated according to age strata.

Conclusion: LOI of the IGF2 gene in PBL appears to be a stable epigenetic phenomenon in most patients. Furthermore, LOI of IGF2 was not associated with age, suggesting an inherited or congenital epigenetic event. These findings support the concept that LOI of IGF2 may be a useful risk factor for CRC predisposition.

Figure 1

(A) ApaI digestion of PCR products amplified from gDNA in ten representative studied cases. Six cases lines 1, 3, 6, 8, 9 and 10 exhibited homozygosis for allele G which contains ApaI site and two bands (204 and 131 bp) are observed after ApaI digestion. Two cases, lines 2 and 5 exhibited homozygosis for allele A which lack the ApaI site and only one band (335 bp) is observed after ApaI digestion. Two cases, lines 4 and 7 exhibited heterozygosity for the allele A and allele G. (B) Electrophoresis of RT-PCR products representative samples. The allele G contains Apa I site and two bands (204 and 131 bp) are observed after ApaI digestion. The allele A lack the ApaI site and only one band (335 bp) is observed after ApaI digestion. Lines 2 and 3 show cases with normal imprinting which express only allele G. Line 5 show a cases with normal imprinting that only express allele A. Cases 1 and 4 show cases with biallelic expression or LOI of IGF2.