[A KEL*02mod allele responsible for an apparent maternity exclusion]. / Un allèle KEL*02mod responsable d'une exclusion apparente de maternité

The patient's rare KEL:1,-2 phenotype was highlighted in course of a routine preoperative erythrocyte typing. Unexpectedly, her two daughters presented a KEL:-1,2 phenotype what appeared first as an apparent maternity exclusion. Flow cytometry, genotyping and adsorption-elution analyses were then performed for those three patients. KEL genotyping showed that the patient's genotype was KEL*01/KEL*02 whereas that of her daughters was KEL*02/KEL*02. By using polyclonal anti-KEL2 reagent, weak amount of KEL2 was identified on the patient's erythrocytes, a result which was confirmed by both flow cytometry and adsorption-elution assays, suggesting that patient's phenotype was in fact KEL:1,2w. These results are in favour of a weak expressed KEL*02 allele (KEL*2mod) transmission coding for a KEL2 antigen detected in some technical conditions only. Those results allowed to explain the apparent maternity exclusion based on initial KEL phenotype. This study also seems to confirm the presence of a compensatory mechanism of the KELmod allele deficient expression in heterozygote patients. A KEL phenotype retrospective study of 80,000 subjects showed a local KEL:1,-2 frequency four times lower than that described in literature. Moreover, a significant number of those individuals would in reality be KEL:1,2w, what still would decrease the real frequency of the KEL:1,2 subjects.

The ABCB6 mutation p.Arg192Trp is a recessive mutation causing the Lan- blood type.

BACKGROUND AND OBJECTIVE: The membrane transporter ABCB6 has recently been shown to carry the high-frequency red-blood-cell (RBC) antigen Lan. All the Lan- individuals genotyped so far have inherited two recessive null mutations in ABCB6. The finding of a family with the Lan- blood type occurring in two successive generations prompted this study. METHODS: Mutations in ABCB6 were searched by Sanger sequencing of exons and flanking intronic regions. Expression analysis of the Lan antigen was carried out by serology and flow cytometry. PCR-RFLP genotyping and Western blot analysis were also applied. RESULTS: All the Lan- members of this family were homozygous for c.574C>T, p.Arg192Trp in ABCB6 while the Lan+ members were heterozygous for this missense mutation encoded by the SNP rs149202834. Homozygosity for p.Arg192Trp was associated not only with absence of the Lan antigen, but also of the ABCB6 transporter in RBC membrane. The complete absence of Lan expression resulting from p.Arg192Trp homozygosity was confirmed by the subsequent identification of five unrelated Lan- individuals who were homozygous for this mutation and who developed an anti-Lan. We also provide evidence that three other single amino acid mutations in ABCB6 (c.826C >T, p.Arg276Trp; c.85_87delTTC, p.Phe29del; c.1762G >A, p.Gly588Ser) may also define ABCB6 null alleles. CONCLUSION: p.Arg192Trp is the first ABCB6 missense mutation causing the Lan- blood type and appears to be a relatively frequent cause of this rare blood type. Like the previously reported frameshift, nonsense and essential splice-site mutations in ABCB6, this missense mutation is recessive and defines an ABCB6 null allele. Other single amino acid mutations in ABCB6 may also cause the Lan- blood type.