chimeras have been defined as individuals whose cells are derived from two or more zygotes ( 1 ) . several different types of chimeras exist ( 2 , 3 ) : artificial chimerism , twin chimerism , and dispermic chimerism . these forms of chimerism are restricted to hematopoietic tissue while dispermic chimeras demonstrate a dual - cell population in disparate body tissues derived from different germ layers ( 3 , 4 ) . chimerism in humans is a rare phenomenon usually identified at the time of blood group determination when mixed field agglutination on the cell typing is noted ( 3 ) . a report of a hemolytic transfusion reaction related to the transfusion of chimeric red blood cells ( rbcs ) has recently been published ( 5 ) . a few cases of phenotypically normal dispermic chimeras have also been reported ( 1 ) . the 47,xyy syndrome is characterized by a male karyotype with an extra copy of the y chromosome . in most cases this chromosomal abnormality causes no unusual physical features or medical problems , especially in men with a mosaic 46,xy/47,xyy karyotype ( 6 ) , hence many males with this syndrome are undetected . we report a case of dispermic chimerism in a 39-yr old korean blood donor who presented with mixed field agglutination in his b antigen typing , and a mosaic 46,xy/47,xyy karyotype . the propositus was a 39-yr old father of one child , healthy , morphologically normal korean male who demonstrated mixed field hemagglutination on cell typing by both the manual tube and gel card techniques at the time of blood donation ( fig . this mixed field agglutination pattern is consistent with an abo subtype that is relatively common in korea known as b3 and is caused by a series of mutant b alleles known collectively as b alleles . to investigate the hypothesis that the mixed field agglutination in the propositus was caused by a b allele , allele - specific polymerase chain reaction ( as - pcr ) and direct sequencing of exons 6 and 7 of the abo gene were performed using previously described methods ( 7 , 8) on the propositus ' genomic dna . however , a careful review of these chromatograms revealed very small b - allele specific peaks at nucleotides 526 , 657 , 703 , 796 , 803 , and 930 ( fig . the former single nucleotide polymorphisms ( snp ) discriminate common o and a alleles from b alleles , while the 261delg snp is only present in common o alleles . in an effort to demonstrate a b allele in the propositus this normal b101 allele was also detected when exons 6 and 7 of the propositus ' abo gene were cloned and sequenced . thus 3 abo alleles , b101 , o01 and o02 , were conclusively demonstrated to be present in the propositus . this confirmed that the mixed field agglutination observed with anti - b reagent indicated the simultaneous presence of two distinct rbc populations ( group b and group o ) in the propositus . the propositus denied receiving a stem cell transplant or transfusion and did not have a known twin , thus chimerism or mosaicism was suspected to explain the presence of the 3 abo alleles . to discriminate chimerism from mosaicism , nine short tandem repeat ( str ) loci were tested on dna extracted from blood , buccal mucosal cells , and hair from the propositus , and on dna isolated from blood on his immediate relatives ( father , mother , and older brother ) . out of 9 str loci , 4 loci ( d3s1358 , d5s818 , d13s317 , and d18s51 ) demonstrated a pattern consistent with a double paternal dna contribution confirming the presence of dispermic chimerism ( fig . 3 ) . to investigate the extent of the propositus ' chimerism , abo typing as well as sequence analysis of abo exon 6 and 7 was performed on his immediate relatives ( table 1 ) . both parents were blood type b and shared the b101 allele while the o01 allele was also detected in the propositus ' mother , and the o02 allele in his father . using sequence - based typing on genomic dna , one paternal and one maternal hla class i ( a , b ) and ii ( drb1 ) haplotype was identified in the propositus ( table 1 ) . analysis of 50 metaphases indicated that the propositus was also a karyotypic mosaic : 32 ( 64% ) metaphases exhibited a normal male karyotype , 46,xy , while 18 ( 36% ) metaphases demonstrated 47,xyy . one of the common presentations of morphologically normal appearing chimeras is an unusual finding in the abo typing such as mixed field rbc agglutination . however , mixed field agglutination can be seen in numerous situations including abo - incompatible stem cell transplantation , rare abo subgroups such as b3 , recent transfusion of type - o rbcs in a non - o recipient , twin chimerism , dispermic chimerism , and mosaicism . most of these entities can be identified by investigating the individual 's clinical and transfusion history or by conducting additional routine serologic tests and/or molecular tests including abo genotyping ( 9 ) . because this healthy and fertile propositus neither had a history of therapeutic transfusion / stem cell transplantation nor knowledge of a twin , we initially suspected a fairly common ( amongst koreans ) group b subtype that classically presents with mixed field agglutination , b3 , as the cause of his unusual cell typing . the unexpected absence of a conclusive b allele by routine abo sequencing led us to suspect the presence of chimerism , and more sensitive abo sequencing techniques were required to reveal a b allele . in the end , a normal b101 allele , in addition to two common o alleles , were discovered in the propositus . assuming that the b101 allele was inherited from his father , the propositus ' abo genotype is most likely b101/o01 and o01/o02 . thus his rbc mixed field agglutination pattern was not due to a b subtype allele , but to the simultaneous presence of group b and o rbcs . as blood group genotyping becomes the mainstream and genotype / phenotype discrepancies are detected more commonly , more cases of chimerism might be detected and thus its true incidence might be uncovered . to determine if the propositus was a chimera or a mosaic , dna polymorphisms from tissues derived from different germ layers were analyzed . dna from the propositus ' hair and buccal mucosa ( ectodermally derived ) and his blood cells ( mesodermally derived ) were tested , and at four loci revealed a pattern consistent with a double paternal dna contribution ( fig . the finding of a double paternal dna contribution in these disparate tissues indicates that the propositus is most likely a dispermic chimera resulting from parthenogenetic division of the ovum and its subsequent fertilization by two spermatozoa carrying different paternal dna - one with a 23,y chromosome complement and another spermatozoa with a different 24,yy dna complement ( 10 ) . alternatively , a non - disjunction event producing the mosaic 47,xyy karyotype could have occurred after fertilization with two different 23,y spermatozoas . this was probably due to a number of factors including the relatively low copy number in the peripheral blood of the second paternal dna contribution , and to the relative insensitivity of whole blood pcr - based techniques for detecting small quantities of dna . in other words , the same reasons we initially failed to detect the b allele from peripheral blood dna were probably the same reasons we did not detect a double paternal hla contribution . a similar phenomenon was also reported by drexler et al . ( 11 ) in their tetragametic chimera , only a single paternal hla haplotype was identified , while both maternal haplotypes were present . the propositus ' karyotype revealed a mosaic pattern with 32/50 metaphases demonstrating 46,xy and 18/50 demonstrating 47,xyy . 47,xyy is a common chromosomal disorder found in approximately 1/1,000 males ( 6 ) . of all cases of 47,xyy syndrome , 80 - 90% are 47,xyy and 10 - 20% are 47,xyy/46,xy ( 6 ) . as with our propositus , the majority of 47,xyy males are phenotypically normal and fertile , bearing chromosomally normal offsprings ( 12 ) . this case represents the first description of a morphologically normal and fertile dispermic chimera with mosaic 47,xyy syndrome .
chimerism in humans is a rare phenomenon often initially identified in the resolution of an abo blood type discrepancy . 
 we report a dispermic chimera who presented with mixed field in his b antigen typing that might have been mistaken for the b3 subtype . 
 the propositus is a healthy korean male blood donor . 
 neither his clinical history nor initial molecular investigation of his abo gene explained his mixed field agglutination with murine anti - b . 
 chimerism was suspected , and 9 short tandem repeat ( str ) loci were analyzed on dna extracted from blood , buccal swabs , and hair from this donor and on dna isolated from peripheral blood lymphocytes from his parents . 
 the propositus ' red blood cells demonstrated mixed field agglutination with anti - b . 
 exon 6 and 7 and flanking intronic regions of his abo gene were sequenced and revealed an o01/o02 genotype . 
 b allele haplotype - specific pcr , along with exon 6 and 7 cloning and sequencing demonstrated a third abo allele , b101 . 
 four str loci demonstrated a pattern consistent with a double paternal chromosome contribution in the propositus , thus confirming chimerism . 
 his karyotype revealed a mosaic pattern : 32/50 metaphases were 46,xy and 18/50 metaphases demonstrated 47,xyy .