Alu sequences represent a specific human family of interspersed repetitive DNA, with a copy number in excess of 500,000 within the human genome. Alu repeats are rarely present in protein-coding regions of mature RNA, and only a few Alu insert mutations have been described so far. In this paper we present an Alu retroposition event in a family with a severe form of hemophilia A. The inserted Alu element belonging to the youngest Yb8 subfamily disrupts the reading frame at methionine 1224, exon 14 of the factor VIII gene, leading to a stop codon within the inserted sequence. This observation indicates that the retroposition of Alu elements is a continuing process possibly generating various human genetic defects.

The Hb F levels in beta-thalassaemia can be affected by factors both linked and unlinked to the beta-globin gene cluster. We have recently analysed a group of patients with a homozygosity for the IVS-I-6 (T-->C) mutation, showing a wide variation in Hb F levels (2-47%) which could not be accounted for by any sequence variation within regulatory elements of the beta-globin gene cluster. In order to further investigate factors underlying this phenotypic difference we have developed a competitive reverse transcription/polymerase chain reaction procedure and used this method to determine the relative amounts of gamma- and beta-mRNAs in 10 patients with the IVS-I-6 homozygosity and 15 heterozygous parents, two IVS-I-6/delta beta-thalassaemia compound heterozygotes, five homozygotes for the beta(+) IVS-I-110 (G-->A) mutation, and in two with a homozygosity for the beta(0) codon 39 (C-->T) mutation. Three heterozygotes were also included. The percentages of gamma/(gamma(+) beta) mRNA were 10-73% in the IVS-I-6 homozygotes and < 2% to 10% in their heterozygous parents. A direct relationship existed between the level of mRNA and the % Hb F. However, the relative gamma-mRNA levels in the IVS-I-6 homozygotes were higher than their Hb F levels, indicating a possible competition between the gamma and beta transcripts for translational factors with a less efficient initiation of protein synthesis on the gamma-mRNA or a preferential survival of cells with mainly beta-globin gene expression at the post-reticulocyte stage. The gamma-mRNA levels in the two IVS-I-6/delta beta-thalassaemia compound heterozygotes were 71% and 62%, similar to their Hb F levels (63% and 59%), and averaged 82% (range 65-91%) in the five IVS-I-110 homozygotes, and 97.5% in the two codon 39 homozygotes. The correlation between these values and the % Hb F could not be evaluated because of the transfusion regimens; however, the levels of gamma-mRNA were as expected for patients with these beta-thalassaemia alleles.

Cord blood samples of 3,232 newborns of different ethnic origins living in the Republic of Macedonia were analyzed by starch gel electrophoresis, polyacrylamide gel electrophoresis and reversed phase high performance liquid chromatography. Hb Bart's was detected in 26 newborns (0.8%) indicating the low incidence of alpha-thalassemia in the Republic of Macedonia. Five different hemoglobin variants (Hb O-Arab, Hb Hamilton, Hb Strumica, Hb F-Macedonia-I, and Hb F-Macedonia-II) were also detected. The levels of the G gamma chains fell into three categories; normal range with G gamma between 50 and 80% (3,143 newborns or 97.2%), low range with G gamma levels of < 50% (35 newborns or 1.1%), and high range with G gamma levels of > 80% (54 newborns or 1.7%). The overall incidence of the A gamma T variant was 20.8%, similar to that found in several Mediterranean populations. DNA analyses showed that the molecular basis of high and low G gamma determinants are heterogeneous in our population. gamma-Gene triplications and the G gamma G gamma arrangements were detected in newborns with high G gamma levels, while gamma gene deletions and A gamma A gamma arrangements were found in newborns with low G gamma levels. All but one of the 135 samples with G gamma between 50 and 80% had the normal G gamma A gamma arrangement on both chromosomes; the only exception was an Albanian newborn (G gamma = 63%) with an-A gamma/G gamma G gamma A gamma arrangement.

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