Genetically determining individualized clinical reference ranges for the biomarker tryptase can limit unnecessary procedures and unmask myeloid neoplasms

Serum tryptase is a biomarker used to aid in the identification of certain myeloid neoplasms, most notably systemic mastocytosis, where baseline (BST) levels >20 ng/mL are a minor criterion for diagnosis. Whereas clonal myeloid neoplasms are rare, the common cause for elevated BST is the genetic trait hereditary alpha-tryptasemia (HαT) caused by increased germline TPSAB1 copy number. To date, the precise structural variation and mechanism(s) underlying elevated BST in HαT and the general clinical utility of tryptase genotyping, remain undefined. Through cloning, long-read sequencing, and assembling of the human tryptase locus from an individual with HαT, and validating our findings in vitro and in silico , we demonstrate that BST elevations arise from over-expression of replicated TPSAB1 loci encoding wild-type α-tryptase due to co-inheritance of a linked over-active promoter element. Modeling BST levels based upon TPSAB1 replication number we generate new individualized clinical reference values for the upper limit of ‘normal’. Using this personalized laboratory medicine approach, we demonstrate the clinical utility of tryptase genotyping, finding that in the absence of HαT, BST levels >11.4 ng/mL frequently identify indolent clonal mast cell disease. Moreover, substantial BST elevations (e.g., >100 ng/mL) which would ordinarily prompt bone marrow biopsy, can result from TPSAB1 replications alone and thus be within ‘normal’ limits for certain individuals with HαT. ### Competing Interest Statement VCU receives royalties from Thermo Fisher for their tryptase test that are shared with LBS as its inventor. None of the remaining authors have relevant conflicts of interest to report. ### Funding Statement This project has been funded in whole or in part with federal funds from the Division of Intramural Research of the National Institute of Allergy and Infectious Diseases, NIH and with federal funds from the National Cancer Institute, National Institutes of Health, under Contract Nos. HHSN261201500003I and 75N910D00024. This project was also funded in part with federal funds from the Division of Intramural Research of the National Heart, Lung, and Blood Institute, NIH. The content of this publication does not necessarily reflect the views or policies of the Department of Health and Human Services, nor does mention of trade names, commercial products, or organizations imply endorsement by the U.S. Government. The involvement of BB and JH was supported by the Intramural Research Program of the National Library of Medicine. SCG is supported by US Public Health Service Grant NIH R21DE028378. VS is a Senior Clinical Researcher of the Research Foundation Flanders/ Fonds Wetenschappelijk Onderzoek (FWO: 1804518N). DE is a Senior Clinical Researcher of the Research Foundation Flanders/Fonds Wetenschappelijk Onderzoek (FWO: 1800614N). ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: Patients, family members, and healthy volunteers provided informed consent on IRB-approved research protocols led by investigators with expertise in Allergy/Immunology at institutions that specialize in clonal and non-clonal mast cell disorders designed to study mastocytosis, or genetic diseases affecting the immune system at the NIH Clinical Center ([NCT00852943][1], [NCT01164241][2], [NCT00044122][3], [NCT00001756][4], NCT007197190), Antwerp University Hospital, Belgium (B300201525454), Verona University Hospital, Italy (protocol No. 39620), the University of Florida (IRB 201702274), the University of Mississippi Medical Center (IRB 2019-0082), or University Clinic Golnik, Slovenia (KME 150/09/13). I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines and uploaded the relevant EQUATOR Network research reporting checklist(s) and other pertinent material as supplementary files, if applicable. Yes All data produced in the present study are available upon reasonable request to the authors. [1]: /lookup/external-ref?link_type=CLINTRIALGOV&access_num=NCT00852943&atom=%2Fmedrxiv%2Fearly%2F2022%2F05%2F02%2F2022.04.29.22274379.atom [2]: /lookup/external-ref?link_type=CLINTRIALGOV&access_num=NCT01164241&atom=%2Fmedrxiv%2Fearly%2F2022%2F05%2F02%2F2022.04.29.22274379.atom [3]: /lookup/external-ref?link_type=CLINTRIALGOV&access_num=NCT00044122&atom=%2Fmedrxiv%2Fearly%2F2022%2F05%2F02%2F2022.04.29.22274379.atom [4]: /lookup/external-ref?link_type=CLINTRIALGOV&access_num=NCT00001756&atom=%2Fmedrxiv%2Fearly%2F2022%2F05%2F02%2F2022.04.29.22274379.atom