[Preliminary linkage analysis of a Chinese family with benign familial infantile convulsion].

OBJECTIVE

Benign familial infantile convulsions (BFIC) is a recently recognized autosomal dominant inherited disorder. This epileptic syndrome typically begins between 3 and 12 months of age with clusters of partial seizures in most cases and carries a good prognosis. So far, three loci have been linked to chromosome 19q12.1-13.1, chromosome 2q24 and chromosome 16p12-q12. The authors performed linkage analysis on this pedigree.

METHODS

A four-generation Chinese family was investigated. The total number of members was 32 in this family and two neurologists in Xiangya Hospital gave systemic physical examinations and interictal neurological examinations to nineteen members of this family. Venous blood samples were taken for genetic analysis. DNA was extracted from peripheral blood leukocytes using phenol-chloroform method. Seventeen microsatellite markers spanning the critical regions on chromosomes 19q12-13.1, 2q24, and 16p12-q12 were genotyped. These markers included D19S49, D19S250, D19S414, D19S416 and D19S245 for the 19q region, D2S2380, D2S399, D2S111, D2S2195, D2S2330 and D2S2345 for the 2q region, D16S401, D16S3131, D16S3093, D16S517, D16S3120 and D16S415 for the 16p-q region. The DNA from each sample was amplified for the 17 markers. After polymerase chain reactions (PCR), PCR products of chromosome 19 with markers D19S49, D19S250, D19S414, D19S416 and D19S245 were subjected to electrophoresis on 8% denatured polyacrylamide gel for at least 2 hours and 20 minutes. Then the length of the PCR products was judged in the Strategene Eagle Eye II automated gel image analyzer. For the markers from chromosome 2 and 16, PCR products were scanned at ABI 377 autosequencer. The data of PCR products were analyzed using the software Genescan v3.1, Genetyper v2.1 (Applied Biosystem, CA. USA) and GenoDB v1.0. After Mendelian checking, the eligible genotyping data were used for linkage analysis. LOD scores were calculated by using MLINK program of LINKAGE v5.1, under an assumption of autosomal dominant inheritance and the estimated penetrance was 0.9. The allele frequencies of each marker were assumed to be equal and the disease-allele frequencies were designated to be 1/10,000. The LOD scores were calculated at combination rate (theta) 0.0, 0.1, 0.2, 0.3, and 0.4.

RESULTS

Among the 17 selected microsatellite markers, which cover the previously reported regions, seven markers' data (D16S3131, D16S517, D16S3120, D16S3093, D2S2380, D19S250 and D19S414) were omitted due to failed genotyping, low genetic heterogeneity, or failure to pass Mendelian checking. Omission of these markers was to ensure the reliability of our raw data. The two-point LOD scores were below zero for all the markers and the maximum LOD scores at theta = 0.0 were less than -2 for markers D19S49, D19S416, D19S245, D16S401, D16S415, D2S399, D2S111, D2S2195, D2S2330 and D2S2345. Thus, the linkage result showed no evidence that the disease locus is linked to any of these selected markers, which excludes the previously reported candidate regions found in other ethnic families.

CONCLUSION

There is no evidence that this Chinese family was linked to one of the following loci: 19q12.1-13.1, 16p12-q12 and 2q24. The results indicated that BFIC showed genetic heterogeneity and the Chinese BFIC families might be mapped on another new locus.