Chitotriosidase Expression in Sarcoidosis Limited by Gene Expression

Sarcoidosis is a multisystem granulomatous disease which affects individuals worldwide of all ages irrespective of ethnicity or race. It is often recognized accidentally when a routine chest radiographic picture shows bilateral hilar lymphadenopathy.

Sarcoidosis patients should undergo multiple clinical examinations including invasive tissue sampling and histopathologic evaluation for definite diagnosis. Several laboratory tests have been developed including serum angiotensin-converting enzyme (ACE) activity which is one of the most frequently measured serum biomarkers having high specificity, but low sensitivity for sarcoidosis.

Clinical scientists at the University of Debrecen (Debrecen, Hungary) enrolled 80 sarcoidosis patients and the diagnosis of sarcoidosis was verified by histopathologic examination of mediastinal lymph node or lung biopsy samples. As controls 133 adults were enrolled who no signs of heart failure (normal ejection fraction). In the case of the sarcoidosis patients, blood samples were taken immediately before biopsy. Genomic DNA was prepared using NucleoSpin Blood kit (Macherey-Nagel GmbH, Düren, Germany).

Serum chitotriosidase (CTO) concentration was measured by two commercially available ELISA kits: Merck KGaA, Darmstadt, Germany and Thermo Fisher Scientific, Waltham, MA, USA. Absorbance values of wells were measured on a ClarioStar microplate reader (BMG Labtech GmbH, Ortenberg, Germany. The team also determined CTO gene duplication polymorphism, direct DNA sequencing of CTO gene and examined cis–trans configuration of CTO gene mutations. The DNA segment was amplified using a Thermo Fisher Scientific Veriti 96-well Thermal Cycler instrument. One of the most frequent polymorphism is caused by a 24-base-pair duplication in exon 10 of the CTO gene (c.1049_1072dup24; rs3831317; referred to as Dup24).

The scientists reported that CTO activities were lower in healthy individuals and sarcoidosis patients heterozygous for Dup24 mutation (472 ± 367 mU/L; 2,300 ± 2,105 mU/L) than in homozygous wild types (838 ± 856 mU/L; 5,125 ± 4,802 mU/L). Sera of Dup24 homozygous individuals had no CTO activity. CTO concentrations were also lower in healthy individuals and sarcoidosis patients heterozygous for Dup24 mutation (7.2 ± 1.9 µg/L; 63.16 ± 56.5 µg/L) than in homozygous wild types (18.9 ± 13.0 µg/L; 157.1 ± 132.4 µg/L) respectively, suggestive for an interaction between Dup24 mutation and CTO concentration determinations.

The authors concluded that the presence of frequent polymorphisms and rare mutations that diminish or abolish CTO activity may hamper the use of CTO as a diagnostic tool in sarcoidosis. These mutations have also effects on currently available CTO concentration measuring techniques, thus CTO activity measurement cannot be replaced by them. Only genotyping of the CTO gene is available to avoid misinterpreting laboratory findings today, furthermore it can assist in recognition of mutations with low allele frequencies in a given population. The study was published on December 8, 2020 in the journal Clinica Chimica Acta.

Related Links:
University of Debrecen
Macherey-Nagel
Merck KGaA
Thermo Fisher Scientific
BMG Labtech