Eine p.Glu419Asp Missense Mutation verursacht eine schwache Expression von KEL1
Sofia Lejon Crottet (Bern / CH), Franziska Still (Bern / CH), Caroline Tinguely (Bern / CH), Rahel Kräuchi (Bern / CH), Christoph Niederhauser (Bern / CH), Bernd Schimanski (Bern / CH), Christine Henny (Bern / CH)
According to the regulations of Blood Transfusion Switzerland, all donors should be tested for the KEL1 (K) antigen. If discrepant or questionable results occur, the KEL1 phenotype must not be interpreted and the obtained blood products must not be released until the discrepancies have been clarified by extended investigations. A routine screening for KEL1 revealed a weakened serologic result for antigen KEL in a first time donor. To solve this discrepancy further investigations were undertaken.
The serological determination for antigen KEL1 was done by standard gel agglutination testing (Grifols). A multiplex SSP-PCR detecting, among others, the single nucleotide variants (SNV) c.578T and c.578C was performed (KEL*01 and KEL*02 resp.). The sample was further investigated by sequencing all 19 KEL exons including flanking intronic regions (Karamatic Crew et al., Vox Sanguinis, 2014). Additionally, RNA was extracted from EDTA whole blood, reverse transcribed and the cDNA was sequenced using an in-house protocol. The effect of the amino acid substitution on the Kell glycoprotein was predicted using PolyPhen-2 (http://genetics.bwh.harvard.edu/pph2/).
The donor sample was serologically typed as KEL:W1 in the routine donor screening. The multiplex SSP-PCR detected the two SNV c.578T and c.578C, thus the predicted genotype KEL*01/KEL*02. By subsequent KEL cDNA sequencing, the SNVs for KEL*01 and KEL*02 and a heterozygous substitution c.1257G>C (p.Glu419Asp) in exon 11 could be identified. Allele-specific sequencing on cDNA revealed that substitution c.1257G>C is located on the KEL*01 allele. According to PolyPhen-2 this substitution is predicted to be probably benign (PolyPhen-2 score 0.267), which is in accordance with the observed phenotype
We present a novel KEL*01.1257C variant causing a weakened expression of KEL1 (GenBank: OQ236611.1). To the best of our knowledge allele KEL*01.1257C has not been reported so far. Patients harboring this KEL1 variant would be considered as KEL:-1, while donors would be considered as KEL:1.
No conflict of interest to declare.