We have investigated the basis of antithrombin deficiency in an asymptomatic individual (and family) with borderline levels (≃70% antigen and activity) of antithrombin. Direct sequencing of amplified DNA showed a mutation in codon 135, AAC to ACC, predicting a heterozygous Asn135Thr substitution. This substitution alters the predicted consensus sequence for glycosylation, Asn-X-Ser, adjacent to the heparin interaction site of antithrombin. The antithrombin isolated from plasma of the proband by heparin-Sepharose chromatography contained amounts of β antithrombin (the very high affinity fraction) greatly increased (≃20% to 30% of total) above the trace levels found in normals. Expression of the residue 135 variant in both a cell-free system and COS-7 cells confirmed altered glycosylation arising as a consequence of the mutation. Wild-type and variant protein were translated and exported from COS-7 cells with apparently equal efficiency, in contrast to the reduced level of variant observed in plasma of the affected individual. This case represents a novel cause of antithrombin deficiency, removal of glycosylation concensus sequence, and highlights the potentially important role of β antithrombin in regulating coagulation.

Familial Overexpression of β Antithrombin Caused by an Asn135Thr Substitution / T.A. Bayston, A. Tripodi, P.M. Mannucci, E. Thompson, H. Ireland, A.C. Fitches, L. Hananeia, R.J. Olds, D.A. Lane. - In: BLOOD. - ISSN 0006-4971. - 93:12(1999 Jun 15), pp. 4242-4247. [10.1182/blood.V93.12.4242]

Familial Overexpression of β Antithrombin Caused by an Asn135Thr Substitution

A. Tripodi
Secondo
;
1999-06-15

Abstract

We have investigated the basis of antithrombin deficiency in an asymptomatic individual (and family) with borderline levels (≃70% antigen and activity) of antithrombin. Direct sequencing of amplified DNA showed a mutation in codon 135, AAC to ACC, predicting a heterozygous Asn135Thr substitution. This substitution alters the predicted consensus sequence for glycosylation, Asn-X-Ser, adjacent to the heparin interaction site of antithrombin. The antithrombin isolated from plasma of the proband by heparin-Sepharose chromatography contained amounts of β antithrombin (the very high affinity fraction) greatly increased (≃20% to 30% of total) above the trace levels found in normals. Expression of the residue 135 variant in both a cell-free system and COS-7 cells confirmed altered glycosylation arising as a consequence of the mutation. Wild-type and variant protein were translated and exported from COS-7 cells with apparently equal efficiency, in contrast to the reduced level of variant observed in plasma of the affected individual. This case represents a novel cause of antithrombin deficiency, removal of glycosylation concensus sequence, and highlights the potentially important role of β antithrombin in regulating coagulation.
Settore BIO/12 - Biochimica Clinica e Biologia Molecolare Clinica
Settore MED/09 - Medicina Interna
Settore MED/15 - Malattie del Sangue
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/2434/189643
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