Examination of a CYP2E1 repeat polymorphism in a monkey model of alcohol abuse

Background: Cytochrome P-450 2E1 (CYP2E1) is involved in alcohol metabolism , and the expression of this enzyme displays wide phenotypic variability in humans. It has been proposed that some of this variability in expression m ay be a consequence of the size of a repeat polymorphism in the 5' regulato ry region of the gene and that the polymorphism may segregate with alcoholi sm. This study examined whether the repeat polymorphism exists in macaque m onkeys and whether it associates with excessive alcohol consumption in this animal model. Methods: Ten outbred cynomolgus monkeys (Macaca fascicularis) that displaye d a voluntary alcohol consumption ranging from 1.0 to 3.6 g/kg/day were gen otyped for a CYP2E1 repeat polymorphism. This polymorphism has been documen ted in the region from -2519 base pair (bp) to -1953 bp of the human CYP2E1 gene 5' distal promoter. Results: Individual polymerase chain reaction amplification of genomic DNA from each of the 10 monkey samples revealed a single band of approximately 400 bp in the region corresponding to the human CYP2E1 polymorphism. Polyme rase chain reaction amplicons from the 10 individuals were sequenced, and e ach one generated a 370 bp sequence that is 90%, identical to the human gen e sequence. However, unlike human alleles that contain five to eight repeat s, the cynomolgus monkey is homozygous for a single copy of the repeat most closely resembling repeat 8 (88% identical) in the human gene. Conclusions: These data demonstrate that the CYP2E1 distal promoter region in monkeys is very similar to the human sequence yet lacks the extensive re peated DNA found in humans. This includes the rare repeats 3 and 4, which h ave been postulated to play a role in transcription regulation and to assoc iate with alcohol abuse liability in humans. These data suggest that the CY P2E1 polymorphism arose late in evolution and that the regulation of the ge ne by this genetic region is not associated with a heavy alcohol drinking p henotype in the cynomolgus monkey.