A mild autosomal dominant form of spondyloepiphyseal dysplasia (SED) is present in several generations of a South African family of English stock. This phenotype differs from that of any other previously described. Although type II collagen defects have been found in some families with SED congenita, the phenotype in our family showed discordant segregation with COL2A1 gene associated restriction fragment length polymorphisms (RFLPs), the markers for the structural locus of type II collagen. It is evident that the SED group of disorders is heterogeneous.
The MN blood group antigens have traditionally been detected by serotyping; however, development of a DNA-based method offers flexibility in the determination of this highly polymorphic system. Genotyping the MN blood group antigens was performed by polymerase chain reaction amplification of the specific alleles (PASA) in the human genome. In separate paired reactions, M or N allele-specific oligonucleotide primers were amplified with a common distal primer. Only in the presence of the homologous template was a 781-base pair polymerase chain reaction amplification product visible after agarose gel electrophoresis and ethidium bromide staining. This method of genotyping could be performed using either 1 microgram of extracted DNA or 0.5 microL of whole blood, and the results showed 100-percent correlation with those obtained by serotyping. PASA-based genotyping of MN blood group antigens, which requires a small amount of starting material, has application in linkage and population studies and in forensic medicine.
The new low-frequency antigen STEM was identified when a Cape coloured woman with an unknown antibody in her plasma (which agglutinated the red cells of her husband and a minority of other individuals) gave birth to a baby suffering mildly from haemolytic disease of the new-born. Most, but not all, examples of anti-STEM distinguish different strengths of STEM antigen on the red cells of different people; the different strengths are inherited. Family studies established that STEM was inherited as a Mendelian dominant character. STEM subdivides hrS-(Rh: -18, -19) and hrB- (Rh: -31, -34) red cells into two types: STEM+ and STEM-. The manually calculated lod score for STEM being associated with the Rh system is 3.91 and LIPED calculated lod score 4.35. The International Society of Blood Transfusion has allocated STEM the Rh number 49.
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