Association between EcoRI fragment-length polymorphism of the immunoglobulin lambda variable 8 (IGLV8) gene family with rheumatoid arthritis and systemic lupus erythematosus

The human immunoglobulin lambda variable 8 (IGLV8) subgroup is a gene family containing three members, one of them included in a monomorphic 3.7-kb EcoRI genomic fragment located at the major lambda variable locus on chromosome 22q11.1 (gene IGLV8a, EMBL accession No. Z73650) at 100% frequency in the normal urban population. The second is a polymorphic RFLP allele included in a 6.0-kb EcoRI fragment at 10% frequency, and the third is located in a monomorphic 8.0-kb EcoRI fragment at 100% frequency, the last being translocated to chromosome 8q11.2 and considered to be an orphan gene. Our Southern blot-EcoRI-RFLP studies in normal individuals and in patients with rheumatoid arthritis (RA) or with systemic lupus erythematosus (SLE), using a specific probe for the IGLV8 gene family (probe pVL8, EMBL accession No. X75424), have revealed the two monomorphic genomic fragments containing the IGLV8 genes, i.e., the 3.7-kb fragment from chromosome 22q11.1 and the 8.0-kb fragment from 8q11.2, both occurring at 100% frequency (103 normal individuals, 48 RA and 28 SLE patients analyzed), but absence of the 6.0-kb IGLV8 polymorphic RFLP allele in all RA or SLE patients. As expected, the frequency of the 6.0-kb allele among the normal individuals was 10%. These findings suggest an association between the absence of the 6.0-kb EcoRI fragment and rheumatoid arthritis and systemic lupus erythematosus.

Correlation between lactose absorption and the C/T-13910 and G/A-22018 mutations of the lactase-phlorizin hydrolase (LCT) gene in adult-type hypolactasia

The C/T-13910 mutation is the major factor responsible for the persistence of the lactase-phlorizin hydrolase (LCT) gene expression. Mutation G/A-22018 appears to be only in co-segregation with C/T-13910. The objective of the present study was to assess the presence of these two mutations in Brazilian individuals with and without lactose malabsorption diagnosed by the hydrogen breath test (HBT). Ten milk-tolerant and 10 milk-intolerant individuals underwent the HBT after oral ingestion of 50 g lactose (equivalent to 1 L of milk). Analyses for C/T-13910 and G/A-22018 mutations were performed using a PCR-based method. Primers were designed for this study based on the GenBank sequence. The CT/GA, CT/AA, and TT/AA genotypes (lactase persistence) were found in 10 individuals with negative HBT. The CC/GG genotype (lactase non-persistence) was found in 10 individuals, 9 of them with positive HBT results. There was a significant agreement between the presence of mutations in the LCT gene promoter and HBT results (kappa = -0.9, P < 0.001). The CT/AA genotype has not been described previously and seems to be related to lactase persistence. The present study showed a significant agreement between the occurrence of mutations G/A-22018 and C/T-13910 and lactose absorption in Brazilian subjects, suggesting that the molecular test used here could be proposed for the laboratory diagnosis of adult-type primary hypolactasia.