['Both gastrin and genetic factors were suggested to underlie the pathogenesis of multiple gastric enterochromaffin-like (ECL) cell carcinoids. To assess the role of genetic alterations in carcinoid tumorigenesis, loss of heterozygosity (LOH) at the locus of the multiple endocrine neoplasia type 1 (MEN-1) gene was studied in gastric carcinoids of patients with MEN-1 and chronic atrophic type A gastritis (A-CAG), as well as in sporadically arising intestinal carcinoids.', 'DNA extracted from archival tissue sections of 35 carcinoid tumors was assessed for LOH with eight polymorphic markers on chromosome 11q13. A combined tumor and family study was performed in 1 patient with MEN-1-Zollinger-Ellison syndrome (ZES).', 'LOH at 11q13 loci was detected in 15 of 20 (75%) MEN-1-ZES carcinoids, and each ECL-cell carcinoid with LOH showed deletion of the wild-type allele. Only 1 of 6 A-CAG carcinoids displayed LOH at the MEN-1 gene locus, and none of the 9 intestinal and rectal carcinoids showed 11q13 LOH.'] Is the multiple endocrine neoplasia type I gene locus involved in the pathogenesis of type II gastric carcinoids?