Molecular and bioinformatic characterization of two novel unstable hemoglobin variants leading to dominant b-thalassemia

SCHEPS, KAREN G.; HASENAHUER, MARCIA ; VARELA, VIVIANA; GARCÍA, ELIANA; CRISP, RENÉE; PARISI, GUSTAVO; FORNASARI, MARÍA SILVINA; TARGOVNIK , HÉCTOR M

Ciudad Autónoma de Buenos Aires

Congreso; Reunión Conjunta de Sociedades de Biociencias. LXII Reunión Anual de la Sociedad Argentinta de Investigación Clínica; 2017

Sociedad Argentina de Investigación Clínica

Although tahalassemic syndromes are typically inherited in a Mendelian recessive manner, dominant forms of β-thalassemia have been described, due to mutations that affect both the structure as well as and the quantity of the synthesized β-globin chains. In this report we present 2 novel small deletions that cause the loss of 2 and 3 amino acids, respectively, leading to dominant unstable variants in 2 pediatric patients. The complete HBB gene of both patients and their parents was cloned in the pGEM®-T Easy Vector Systems and sequenced. The altered amino acid sequences were studied analyzing their physicochemical properties, sequence conservation and secondary and tertiary structure predictions. The first patient presented the deletion HBB:c.29_37delCTGCCGTTA (p.Ala10_Thr12del) in heterozygote state. The new variant was given the name Hb JC Paz. As a result of this mutation, an Alanine,a Valine and a Threonine of the ?A? α-helix of the β-globin chain are deleted. These deleted residues are closed to N-term and at least one α-helix turn is expected to be lost. Moreover this alteration could affect the polar interactions of V1 and H2 with the allosteric modulator 2,3-diphosphoglycerate. The second proband presented the mutation HBB:c.182_187delTGAAGG (p.Val60_Lys61del) in heterozygote state, resulting in the variant named Hb Tavapy. Consequence of this deletion, the Valine and Lysine of codons 60 and 61 are lost, altering the globular structure of the modified chain. Provean sequence based prediction of p.Val60_Lys61del indicates a deleterious effect with a strong score. Furthermore, deleted residues are close to the distal histidine (H63) in the heme pocket. Both deletions arose as de novo mutations. The predicted structural models provided a feasable explanation for the clinical outcomes observed in the patients and offered additional insights to the importance of key amino acids in the b-globin chain.