From the investigation of RHD-CE hybrid genes to the recognition of RHCE variants and RHD zygosity. Expanding the analysis by QMPSF in Brazilian donors and in patients with sickle cell disease.

BACKGROUND: Hybrid genes are responsible for the formation of Rh variants and are common in patients with sickle cell disease (SCD). However, it is not usually possible to detect them by conventional molecular protocols. In the present study, hybrid genes were investigated using the Quantitative Multiplex Polymerase chain reaction of Short Fluorescent Fragments (QMPSF), a molecular protocol that quantifies the copy number of RHD and RHCE exons. In addition, we explored additional relevant information obtained with QMPSF, such as recognition of variant RHCE and RHD zygosity. MATERIALS AND METHODS: Three groups of subjects were selected for the study: patients with SCD, self-declared African descent donors (SDA), and D-negative donors. RHD and RHCE hybrids genes were investigated by the QMPSF method. Real-time multiplex polymerase chain reaction (PCR) assay was used to confirm the copy number of the RHD in two samples. Cloning was performed to investigate the allele. Relative RhD antigen density was investigated by flow cytometry, and RhCE phenotyping was performed with both tube and gel methods. RESULTS: In the 507 samples analysed, hybrid allele frequencies were found in 20.08% of patients with SCD, in 18.22% of individuals in the SDA group, and 3.67% of D-negative donors. The SCD and SDA groups had a higher frequency of hybrid alleles, most commonly involving exon 8, with which we found an association with c.733C>G, a common polymorphism observed in individuals of African descent. Of note, two patients with SCD were shown to carry three gene copies, as confirmed by quantitative PCR; no increase in D expression was observed in these patients. In addition, the QMPSF guided the investigation of 144 RHCE variants and RHD zygosity, and two novel alleles were identified. DISCUSSION: The QMPSF was shown to identify hybrid alleles involved in altered Rh phenotypes in Brazilian donors and patients with SCD. The association of the hybrid RHCE-D(8)-CE allele with c.733C>G suggests this hybrid allele may be used as a marker to detect the most frequent variants found in patients with SCD.

SMIM1 polymorphisms in a donor population from southeast Brazil and their correlation with VEL expression.

BACKGROUND: Vel is a high frequency blood group antigen and its alloantibody is involved in haemolytic transfusion reactions. After elucidation of the molecular basis of the Vel-negative phenotype defined by a 17-base pair deletion in SMIM1, genotyping has been the technique of choice to identify the Vel-negative phenotype, and molecular investigations have contributed to explain Vel expression variability. The present study was aimed at screening for Vel negative blood donors and characterising the genetic changes found in Brazilian donors with altered Vel expression. MATERIALS AND METHODS: Molecular screening for the SMIM1*64_80del allele was performed in 1,595 blood donor samples using a SNaPshot protocol previously standardised in our laboratory. Four hundred donor samples were also submitted to serological screening using a polyclonal anti-Vel from our inventory. Samples with variability in antigen strength were selected for SMIM1 sequencing. RESULTS: No homozygous SMIM1*64_80del allele was found and the SMIM1*64_80del allele frequency was 1.01%. Different patterns of reactivity were observed in serological testing varying from negative to 3+. Through sequencing analysis we highlighted two polymorphisms: rs1175550 and rs6673829. The minor G allele of rs1175550 was found in 16/20 samples reacting 3+, while the major A allele was found in 21/23 samples reacting 2+. Regarding rs6673829, the minor A allele was present in 14/23 and 3/20 samples reacting 2+ and 3+ respectively. DISCUSSION: We included molecular VEL screening in a previously standardised SNaPshot protocol, which besides enabling detection of Vel-negative donors, also searches for eight other rare blood types. Additionally, the present study demonstrated that although the SMIM1*64_80del allele is responsible for some variation of Vel phenotype in this donor population, Vel expression is also controlled by molecular changes in SMIM1 intron 2.