Molecular characterisation of the defective alpha 1-antitrypsin alleles PIMwurzburg (Pro369Ser), Mheerlen (Pro369Leu), and Q0lisbon (Thr68lle)

Deficiency of the serine proteinase inhibitor (serpin) alpha 1-antitrypsin (alpha 1AT) is the most common autosomal recessive genetic disorder in Nort hern Europe. alpha 1AT is the physiological regulator of the proteolytic en zyme neutrophil elastase and severe deficiency states are associated with a n increased risk of developing chronic obstructive pulmonary disease (COPD) as a consequence of chronic proteolytic damage to the lungs. Among the kno wn mutations of the alpha 1AT gene causing severe alpha 1AT deficiency and COPD a few alleles are also associated with liver disease, When expressed i n cell cultures, all these particular alleles cause intracellular alpha 1AT accumulation which appears to be a prerequisite for the development of hep atic injury, Liver disease is seen in only a small fraction of all patients carrying such alleles, however. The reason for this is not completely clea r, but there is evidence that PI ZZ individuals 'susceptible' to liver dise ase carry an additional defect affecting protein degradation in the endopla smic reticulum (ER), We characterise a newly identified defective alpha 1AT allele PI Mwurzburg (Pro369 [(C) under bar CC] to Ser [(T) under bar CC]) associated with a complete intracellular transport block in cell cultures i n vitro, The allele PI Mheerlen, a previously described different amino aci d substitution in the same position as PI Mwurzburg (Pro369 [C (C) under ba r C] to Leu [C (T) under bar C]) is shown to cause complete retention of th e mutant alpha 1AT in the ER, too, whereas in the recently described mutant allele PI Q0lisbon (Thr68 [A (C) under bar C] to Ile [A (T) under bar C]) a significantly reduced alpha 1AT secretion from the cells was observed. Ad enovirus-mediated recombinant expression of mutant Mwurzburg and Mheerlen, and of wild-type alpha 1AT in mouse liver in vivo showed that the mutant hu man proteins were not secreted into the mouse plasma, in contrast with huma n wild-type alpha 1AT which circulated at high concentrations over several weeks, In summary, all transportation deficient alpha 1ATs analysed have th e potential to cause lung disease in the homozygous state or in heterozygou s carriers of another deficiency allele, and they may also cause liver dise ase in certain patients, The mutant PI Mwurzburg and Mheerlen alpha 1ATs ar e completely retained within synthesising cells, and the molecular defect o f transportation in these two alleles may be similar to that in the common PI Z allele. The molecular defect in the PI Q0lisbon allele (Thr68Ile) show s similarity with the immediately neighbouring Mmineral springs mutation (G ly67Glu).