Abstract-Familial combined hyperlipidemia (FCHL), the most common familial dyslipidemia, is implicated in up to 20% of cases of premature coronary heart disease. Although underlying mutations for FCHL have yet to be identified, several candidate genes/regions have been identified. A positive linkage to chromosome 1q markers has been reported, with the highest lod score of 5.93 occurring at a location between D1S104 and D1S1677. Using the same diagnostic criteria, the Family Heart Study (FHS) has defined 71 FCHL families, comprising 170 cases, for a total of 137 possible affected sibling pairs. The FCHL criteria require elevation in serum low density lipoprotein cholesterol and triglyceride levels within the family, with at least 2 affected first-degree relatives. Markers D1S104 and D1S1677 were typed, and significant allele sharing was found in FCHL sibships (multipoint lod score with use of the model from the Finnish study was 2.52, and multipoint nonparametric score was 2.48; Pϭ0.007), replicating linkage in this chromosome 1 region. In addition, previously reported linkage of FCHL to apolipoprotein A-I/C-III/A-IV has been investigated in FHS families. FHS results revealed positive but nonsignificant allele sharing among FCHL sibships with apolipoprotein A-I/C-III/ A-IV by use of marker D11S4127 (nonparametric linkage score 1.11, Pϭ0.13). Two-locus analyses of D1S104 and D11S4127 suggested possible heterogeneity rather than epistasis, with a maximum 2-locus lod score of 3.05. A nonparametric 2-locus analysis revealed significant improvement in the 2-locus versus single-locus scores. Key Words: genetic linkage Ⅲ coronary disease Ⅲ hyperlipidemia F amilial combined hyperlipidemia (FCHL) is the most common familial dyslipidemia, with a prevalence of 1% to 2%, 1 and is implicated in up to 20% of cases of premature coronary heart disease (CHD). 2 FCHL criteria require elevation of serum total cholesterol and triglyceride levels within the family, with at least 2 affected first-degree relatives. 3 Studies of the genetics of FCHL have been complicated by uncertain phenotype definition, likely genetic heterogeneity, and unknown mode of inheritance. These difficulties have thus far prevented the identification of underlying mutations for FCHL. Several loci have produced positive results, although often with mixed findings in replication studies.Perhaps the most promising candidate region is on chromosome 1q21-23. Pajukanta et al 4 recently published positive linkage to chromosome 1q markers in 250 individuals (115 affected) from 31 Finnish FCHL families, with the highest lod score of 5.93 occurring between D1S104 and D1S1677.