The Relative Levels Of Alpha(2)-, Alpha(1)-, And Zeta-Mrna In Hb H Patients With Different Deletional And Nondeletional Alpha-Thalassemia Determinants

Abstract

We have analyzed the alpha(2)/alpha(1)-, alpha/beta-, zeta/(alpha + zeta)-mRNA ratios in the: retic-ulocytes of 40 patients with Hb H disease. 21 patients had deletional Hb H disease (- - / - alpha), namely combinations of one of four types of alpha-thal-1 (MED-I, MED-II, -(alpha)20.5, SEA) and one of two types of alpha-thal-2(- 3.7 or - 4.2 kb): 13 had Hb H disease because of combinations of one of these alpha-thal-1 deletions with either a 5 nt deletion at the 5' splicing site of IVS-I, or a terminating codon mutation (Hb CS), or a poly(A) mutation, and six were homozygous for either a poly(A) mutation or the 5 nt deletion. Significant differences were observed between the deletional types (- - /- alpha; alpha(2)/alpha(1) ratio of zero; alpha/beta ratio of similar to 1) and non-deletional types (- - /alpha(T) alpha; alpha(2)/alpha(1) ratio of 0.05-0.3 for those with T = the 5 nt deletion or the terminating codon mutant, and similar to 1.0 for those with T = a poly(A) mutation; alpha/beta ratio in all types of similar to 0.7). Comparable data were found for the nondeletional alpha-thal-2 homozygotes. The noted differences were highly significant and the determination of the two ratios may be diagnostically of considerable value. The Low alpha(2)/alpha(1)-mRNA ratio in the two patients- with - - /alpha(-5nt)alpha and the one patient with alpha(-5nt)alpha/alpha(-5nt)alpha indicates the presence of minute amounts of alpha(2)-mRNA; apparently splicing at the donor site is greatly impaired by this a deletion but not eliminated. The high alpha(2)/alpha(1)-mRNA ratio in the four patients with - -/alpha(PA-2)alpha and the five patients with alpha(PA-1)alpha/alpha(PA-1)alpha (PA-1 and PA-2 are poly(A) mutations) is due to the presence of an elongated alpha(2)-mRNA which uses an alternate location as a polyadenylation site. The relative levels of zeta-mRNA varied considerably the highest levels were found in patients with the -(alpha)20.5/-alpha (SEA)/ - alpha deletional types but not in those with the - (alpha)20.5/-alpha or - -(SEA)/-alpha deletional types but not in those with the -(alpha)20.5/alpha(PA-2)alpha, -(alpha)20.5/alpha(-5nt)alpha, or - -(SEA)/alpha(CS)alpha nondeletional types. No definitive explanation can be given for these differences; perhaps certain sequences that are part of some of the alpha-thal-1 deletions are important for the suppresstion of the zeta-globin gene.