5.2　The CEL-HYB Allele Probably Represents an Ethn...

5.2　The CEL-HYB Allele Probably Represents an Ethnicity-Specific Risk Factor

Fig.6.1　（a）Key differences between CEL-HYB1［originally termed CEL-HYB（Fjeld et al.2015）］，CEL-HYB2 and the wild-type CEL gene in terms of the defining exon 10，intron 10 and exon 11 sequences.The gene structure of CEL（in black）and that of the replacement CELP sequences（in green）within CEL-HYB1 and CEL-HYB2 were described in accordance with GenBank accession number AF072711.1.In CEL，the VNTRs within exon 11 are indicated in purple；nucleotide positions of the exon 10 boundaries and the beginning of exon 11 are numbered by reference to the A of the translational initiation codon ATG as c.1；the translational termination codon is denoted by a vertical blue bar，with the last coding nucleotide and the amino acid position of the translational termination codon being numbered above and below the bar.In CEL-HYB1，CEL-HYB2a and CEL-HYB2b，the presumed premature stop codons are indicated in a similar manner.（b）A representative gel showing the RT-PCR analyses of HEK293T cells transfected with expression constructs The patients analysed in the Fjeld study were solely of European ancestry（Fjeld et al.2015）.We therefore attempted to replicate the association between CEL-HYB and chronic pancreatitis in three Asian（Chinese，Japanese，and Indian）populations.Contrary to expectation，we failed to identify the aforementioned CEL-HYB allele in any of our three cohorts（Zou et al.2016c）.Instead，we found an alternative CEL-HYB allele，which was not found to be associated with ICP in any of our cohorts.This alternative allele resulted from an NAHR event occurring within a 239-bp sequence tract affecting the intron 9/exon 10 boundary of CEL and the intron 9'/exon 10'boundary of CELP（Fig.6.1a）.To distinguish the two CEL-HYB alleles，we termed them respectively CEL-HYB1 and CEL-HYB2.CELHYB2 was further divided into two subtypes by reference to three SNPs present within the substituting CELP sequence（Zou et al.2016c）.carrying the full-length CEL-HYB1 and CEL-HYB2a genomic sequences.Sanger sequencing of the approximately 2.2-kb CEL-HYB1 and CEL-HYB2a products revealed that all introns were spliced correctly.CV control vector.（c）Relative mRNA expression levels of CEL-HYB2a versus CEL-HYB1 in vitro as determined by quantitative RT-PCR analyses.CV control vector.（d）Relative mRNA expression levels of CEL-HYB2a in transfected cells with（grey）and without（black）cycloheximide treatment as determined by quantitative RT-PCR analyses.**P＜0.01.Reprinted from Gastroenterology，Vol 150，Zou WB，Boulling A，Masamune A，Issarapu P，Masson E，Wu H，Sun XT，Hu LH，Zhou DZ，He L，Fichou Y，Nakano E，Hamada S，Kakuta Y，Kume K，Isayama H，Paliwal S，Mani KR，Bhaskar S，Cooper DN，Férec C，Shimosegawa T，Chandak GR，Chen JM，Li ZS，Liao Z，No association between CEL-HYB hybrid allele and chronic pancreatitis in Asian populations，1558-1560.e5，Copyright（2016），with permission from Elsevier

The allele frequency of CEL-HYB1 in healthy German and French populations is approximately 0.4%（Fjeld et al.2015）.CEL-HYB1 thus falls into the category of rare variants in accordance with current terminology（Manolio et al.2009；Tennessen et al.2012）.Given that most rare variants are population-specific（Tennessen et al.2012），CEL-HYB1 most likely represents an ethnicity-specific disease risk factor.This issue could be clarified by the analysis of CEL-HYB1 in an independent cohort of European ancestry such as the North American Pancreatitis Study II cohort（LaRusch et al.2015）.(https://www.daowen.com)