John G. Gilman

Diminished AγT fetal globin levels in Sardinian haplotype II β°‐thalassaemia patients are associated with a four base pair deletion in the AγT promoter

Summary In Sardinia, the β‐39 nonsense mutation is the primary cause of β°‐thalassaemia. This mutation is found mainly on β‐globin gene cluster haplotypes I and II, which differ in their Aγ globin types (AγI and AγT, respectively). This report presents data on Gγ, AγI and AγT levels, and the presence or absence of a 4 base pair (bp) deletion at ‐225 to ‐222 of the Aγ globin promoter, in 55 poly‐transfused β°‐thalassaemia major patients. Six patients were homozygotes for the normal (N) Aγ promoter lacking the 4 bp deletion, had no AγT globin, and their mean Gγ:AγI:AγT ratio was 52·9:47·1:0. Twenty‐five patients were homozygotes for the mutant (M) Aγ promoter with the 4 bp deletion, had no AγI globin, and the mean Gγ:AγI:AγT ratio was 62·1:0:37·9. For M/M compared to N/N, the lower AγT than AγI was significant by the t‐test (P<0·001). Twenty‐four N/M cases had mean Gγ:AγI:AγT of 56:24·4:19·6, and the lower AγT than AγI was also significant (P<0·001). Partial haplotype analysis on these and 17 other β°‐thalassaemia patients suggested that the 4 bp deletion was strongly associated with haplotype II. Of 33 M/M, 32 were haplotype II/II and one was II/5a; of 31 N/M, 29 were I/II and two were II/IX; of eight N/N, seven were haplotype I/I and one was I/IX. These data show a strong association of the 4 bp promoter deletion with decreased expression of the AγT globin gene on haplotype II.

The 32·6 kb Indian δβ‐thalassaemia deletion ends in a 3·4 kb L1 element downstream of the β‐globin gene

Summary. The Indian δβ‐thalassaemia, with elevated fetal γ globin gene expression, was previously found to have a large deletion beginning 1 kb 3’of the Aγ globin gene at GenBank HUMHBB coordinate 42151, and extending into a new L1 sequence. We have now determined the 3’breakpoint of this deletion, and in doing so we have extended the known β‐globin gene cluster DNA sequence from its end at 73326 to projected GenBank coordinate 79016. These data show that the deletion is 32–6 kb long, terminating 11 kb 3’of the β‐globin gene. This 3’breakpoint is at 74772, within a 3.4 kb partial L1 repeat at 74263–77665; the Black (Aγδβ)°‐thalassaemia also terminates in this L1, at 76508. In addition, two Alu sequences were found, at 73692–73816 and 78171–78441. Among the protein‐binding DNA sequence motifs 3’to the Indian δβ‐thalassaemia breakpoint, at 76581/76607 there is a TGATAA/ACACCC pair that binds the erythroid‐specific GATA‐1 and ubiquitous CACCC‐box binding proteins. We hypothesize that elevated fetal haemoglobin may be due to an enhancer or enhancers 3’to the deletion breakpoints and may involve the TGATAA/ ACACCC pair.