L-H. Gu

The dominant β-thalassaemia in a Spanish family is due to a frameshift that introduces an extra CGG codon (=arginine) at the 5' end of the second exon

We have discovered a Spanish family with a dominant type of β‐thalassaemia. Carriers are characterized by mild anaemia, hypochromia, microcytosis, elevated Hb A2 and Hb F levels, reticulocytosis, and splenomegaly. The molecular basis of this condition is the introduction of a CGG triplet between codons 30 and 31 of the β gene; this was determined by sequencing of amplified DNA and confirmed by dot‐blot analysis. The abnormal mRNA (βTh‐mRNA) is stable and present in quantities similar to that of normal βA‐mRNA. cDNA fragments derived from βTh‐ and βA‐mRNAs can be separated on a denaturing polyacrylamide gel electrophoresis because the βTh fragment is three nucleotides (nts) longer than the βA fragment. The βTh‐mRNA translates into a β chain that is 147 amino acid residues long and carries an extra arginine residue between residues 30 and 31. This βX chain has not been detected. It may be unstable and does not bind to the α chain. It probably is continuously digested by proteolytic enzymes in red cell precursors in the bone marrow. The abnormal chain probably binds haem that is excreted after proteolysis causing a darkening of the urine.

Alpha-, beta-, and gamma-mRNA levels in beta-thalassemia; transcriptional and translational differences in heterozygotes, homozygotes, and compound heterozygotes.

We have determined the relative levels of alpha-, beta-, and gamma- (G gamma- and A gamma-) mRNAs in the reticulocytes of patients with mild beta-thalassemia intermedia due to combinations of promoter mutations and a classical type of beta-thalassemia, as well as in their relatives. The expected differences in the alpha/beta-mRNA ratio confirmed the mild suppression of beta-mRNA synthesis, particularly in heterozygotes for the -101 (C-->T) promoter mutation and the large increase in the relative gamma-mRNA level in compound heterozygotes. A significant discrepancy between Hb F and gamma-mRNA levels, observed in previously published studies, was confirmed indicating a less efficient gamma-mRNA translation. When the two different gamma-mRNA (G gamma- and A gamma-) levels were determined it was observed that in beta-thalassemia heterozygotes the extra gamma-mRNA was primarily of the G gamma type suggesting a more efficient translation of the A gamma-mRNA. This difference disappeared in homozygotes and compound heterozygotes: both mRNAs (G gamma- and A gamma-) translate with an equal efficiency.

A new Variant, Hb Muscat [α2β232(B14)Leu→val] Observed in Association With Hb S in an Arabian Family

The silent Hb Muscat with a Leu→Val replacement at position β32 was discovered by reversed phase high performance liquid chromatography in two members of an Arabian family from Oman; in one person Hb Muscat occurred with Hb S and in the other with Hb A. Hb Muscat is slightly unstable but its presence has no apparent adverse effect on the health of its carriers. Additional hemoglobin abnormalities observed in this family were a common a-thal-assemia-2 (-3.7 kb) and Hb S. The βS haplotypes in the heterozygous carriers and the two sickle cell anemia patients were #19 (Benin) and #20 (Bantu); the latter likely originated from an East African population.

The Relative Levels of Different Types of β-mRNA and β-Globin in BFU-E Derived Colonies from Patients with β Chain Variants; Further Evidence for Somatic Mosaicism in the Hb Costa Rica Carrier [β77(EF1)HISÅG]

We have identified and quantitated the different types of mRNA in single BFU-E derived colonies from Hb S and Hb Atlanta [beta 75 (E19)Leu-->Pro] heterozygotes and observed that the normal and mutated mRNAs were present in equal quantities. Similar studies for the different protein products gave less accurate data because high performance liquid chromatography methods were not sensitive enough for the analysis of a single colony, and as many as five colonies needed to be combined. The level of Hb S (approximately 40%) was the same as in red cell lysates of the Hb S heterozygote, while that of the unstable beta-Atlanta chain was lower than expected from the values observed in red cells. Similar studies for a carrier of the stable Hb Costa Rica [beta 77(EF1) His-->Arg] which was reported to be the result of a somatic cell mutation (1) gave quite different data. Dot-blot analysis with 32P-labeled probes and allele specific amplification methodology identified numerous colonies with beta A-mRNA only, while 12-15% of the colonies contained both beta A- and beta-Costa Rica-mRNA. This limited distribution of the beta-Costa Rica-mRNA was confirmed by hemoglobin analysis with anion exchange high performance liquid chromatography. These results are considered to provide additional and convincing evidence for a somatic mosaicism for the CAC-->CGC mutation at codon 77 of the beta gene which occurred during the development of the embryo and results in the presence of only some 6-8% of the abnormal Hb Costa Rica in the circulating red cells.

Black α-Thalassemia-1: Partial Characterization of an ∼80 KB Deletion Which Includes the ξ- and α-Globin Genes

A large novel α-thalassemia-1 deletion which includes the ξ-, α2-, α1-, and θ1-globin genes is described in a Black family living in Georgia and Florida. The deletion which was characterized by restriction enzyme analysis, extends 15 to 35 kb 5′ and at least 35 kb 3′ to the Cap site of the ξ-globin gene. Mental retardation was not observed. The deletion was present in a 35-year-old male with Hb H disease and his mother; the major hemoglobin type in the propositus was Hb G-Philadelphia or α268(E12)Asn→Lyss2 because his second chromosome carried the -αG(-3.7 kb) α-thalassemia-2 deletion.