PURPOSETo identify the genetic basis of posterior amorphous corneal dystrophy (PACD) segregating in a large pedigree.METHODSThe authors performed clinical evaluation of a previously unreported pedigree with PACD, light and electron microscopic examination of an excised corneal button, genomewide linkage analysis, fine mapping linkage and haplotype analysis, and screening of four candidate genes (KERA, LUM, DCN, and EPYC).RESULTSTwenty-one participants were determined to be affected based on the presence of characteristic clinical features of PACD; 15 affected and 39 unaffected individuals from a single pedigree enrolled in the study and provided DNA for analysis. Histopathologic examination of an excised corneal specimen from an affected individual demonstrated disorganized stromal lamellae and stromal staining with colloidal iron. Genomewide analysis demonstrated significant evidence of linkage to chromosome region 12q21.33 and evidence suggestive of linkage to chromosome region 8q22.3. Fine mapping of the chromosome 12 locus confirmed significant linkage; the largest multipoint log odds ratio score was 5.6 at D12S351. The linkage support interval was approximately 3.5 Mb (3.5 cM) in length between flanking markers D12S1812 and D12S95, roughly the entire chromosome band 12q21.33. No coding region mutations were identified in four candidate genes-KERA, LUM, DCN, EPYC-located in the chromosome 12 linkage support interval.CONCLUSIONSLinkage and haplotype analyses identified 12q21.33 as a locus for PACD. However, no mutations were identified in the candidate genes (KERA, LUM, DCN, EPYC) within this region.