Stepwise partitioning of Xp21: a profiling method for XK deletions causative of the McLeod syndrome.

Gassner C, Brönnimann C, Merki Y, Mattle-Greminger MP, Sigurdardottir S, Meyer E, Engström C, O’Sullivan JD, Jung HH, Frey BM.

Abstract

Background

McLeod syndrome (MLS) is hematologically defined by the absence of the red blood cell (RBC) antigen Kx on the transmembrane RBC protein, XK, representing a highly specific diagnostic marker. Direct molecular assessment of XK therefore represents a desirable diagnostic tool. Whereas pathogenic point mutations may be simply identified, partial and complete deletions of XK on Xp21.1, eventually covering adjacent genes and causing multifaceted “continuous gene syndromes,” are difficult to localize.

Study Design And Methods

Three different McLeod patient samples were tested using 16 initial positional polymerase chain reaction (PCR) procedures distributed over an approximately 2.8-Mbp Xp-chromosomal region, ranging telomeric from MAGEB16 to OTC, centromeric of XK. The molecular breakpoint of one sample with an apparent large Xp deletion was iteratively narrowed down by stepwise positioning further PCR procedures and sequenced. Two mutant XK genes, one previously published and serving as a positive control, were also sequenced.

Results

We confirmed the positive control as previously published and listed as XKN.20 by the International Society of Blood Transfusion (ISBT). The other XK showed a novel four-nucleotide deletion in Exon 1, 195-198delCCGC (newly listed as XKN.39 by the ISBT). The third sample had an approximately 151-kbp X-chromosomal deletion, reaching from Exon 2 of LANCL3, across XK to Exon 3 of CYBB (newly listed as XKN.01.016 by the ISBT). Carrier status of the patients’ sister was diagnosed using a diagnostic “gap-PCR.”

Conclusions

The stepwise partitioning of Xp21.1 is pragmatic and cost-efficient in comparison to other diagnostic techniques such as “massive parallel sequencing” given the rarity of MLS. All males with suspected MLS should be considered for molecular XK profiling. © 2017 AABB.

PMID: 28555782 DOI: 10.1111/trf.14172