[Clinical, biochemical and epidemiological features of macro-AST preceding inflammatory bowel disease diagnosis by several years]

INTRODUCTION

An isolated elevation of aspartate aminotransferase (AST) is a diagnostic issue. Macro-aspartate aminotransferase (macro-AST) corresponds to the formation of complexes between AST and immunoglobulins.

CASE REPORT

We report the case of a patient with macro-AST identified several years before the onset of inflammatory bowel disease (IBD). A 6-year retrospective analysis in our laboratory identified only one case out of 42 540 adult patients.

CONCLUSION

The objective of this work is to increase awareness of this benign disorder among clinicians and biologists, as well as to aid in prescribing only the required tests.

A heterozygous mutation in GOT1 is associated with familial macro-aspartate aminotransferase

BACKGROUND & AIMS

Macro-aspartate aminotransferase (macro-AST) manifests as a persistent elevation of AST levels, because of association of the protein with immunoglobulins in the circulation. Macro-AST is a rare, benign condition without a previously confirmed genetic basis.

METHODS

Whole exome sequencing (WES)-based screening was performed on 32 participants with suspected familial macro-AST, while validation of variants was performed on an extended cohort of 92 probands and 1,644 healthy controls using Taqman genotyping.

RESULTS

A missense variant (p.Gln208Glu, rs374966349) in glutamate oxaloacetate transaminase 1 (GOT1) was found, as a putative causal variant predisposing to familial macro-AST. The GOT1 p.Gln208Glu mutation was detected in 50 (54.3%) of 92 probands from 20 of 29 (69%) families, while its prevalence in healthy controls was only 0.18%. In silico analysis demonstrated that the amino acid at this position is not conserved among different species and that, functionally, a negatively charged glutamate on the GOT1 surface could strongly anchor serum immunoglobulins.

CONCLUSIONS

Our data highlight that testing for the p.Gln208Glu genetic variant may be useful in diagnosis of macro-AST.

LAY SUMMARY

Higher than normal levels of aspartate aminotransferase (AST) in the bloodstream may be a sign of a health problem. Individuals with macro-AST have elevated blood AST levels, without ongoing disease and often undergo unnecessary medical tests before the diagnosis of macro-AST is established. We found a genetic variant in the GOT1 gene associated with macro-AST. Genetic testing for this variant may aid diagnosis of macro-AST.

[Macro-AST and myeloma: An incidental association?]

INTRODUCTION

Macro-AST is recognized as a classical aetiology of isolated and persistent increase of serum aspartate aminotransferase (AST) levels. Macro-AST are high molecular weight complexes associating AST and a macromolecule, often an immunoglobulin. Although those macroenzymes of unknown pathogenesis are usually non-pathogenic, association with several diseases, including autoimmune diseases and liver diseases has been described.

CASE REPORT

We report here the case of a 45-year-old patient with previously normal liver enzymes in whom an AST elevation and an IgA monoclonal gammopathy were discovered concomitantly. Following the diagnosis of multiple myeloma, we could evidence in the patient's serum a complex between AST and the monoclonal IgA. AST levels course followed closely the progression of monoclonal gammopathy.

CONCLUSION

This is the first report demonstrating a clear link between macro-AST and a monoclonal gammopathy.