A NUCLEOTIDE INSERTION IN EXON-4 IS RESPONSIBLE FOR THE ABSENCE OF EXPRESSION OF AN HLA-A-ASTERISK-01 ALLELE

HLA class I typing performed in parallel by molecular biology and sero logy has revealed cases where an HLA class I allele was identified whe reas the corresponding antigen was not detected on the cell surface. I n the present report, we describe four members of a family in whom an HLA-A1 allele identified at the molecular level was typed as A ''blank '' by lymphocytotoxicity. This serologically blank antigen was undetec table by isoelectric focusing (IEF). Sequencing of the HLA-A01 allele from the promoter region to the eighth exonic region revealed inserti on of a ''C'' nucleotide at the beginning of the fourth exon as compar ed to the common HLA-A0101 allele. This mutation causes a frame shift , giving rise to an early stop codon in the fourth exon.