Common Variable Immunodeficiency (CVID) in Adults As First Manifestation of (cryptic) Dyskeratosis Congenita

Introduction: Dyskeratosis Congenita (DKC) is caused by mutations in genes related to telomere maintenance resulting in prematurely shortened telomeres. Clinically, classical DKC is characterized by mucocutaneous abnormalities, bone marrow failure and other variable features such as lung or liver fibrosis. In adults, mono- or oligosymptomatic DKC is typically presenting with a clinically more heterogeneous and often cryptic picture without classical symptoms of DKC. Data on immunodeficiency as a predominant symptom in DKC patients is limited. The common variable immunodeficiency (CVID) represents a heterogenous group of disease with no universally accepted definition. Typically, patients show hypogammaglobulinaemia and impaired vaccine response. In most cases the genetic basis of CVID remains unknown and to date, the disease is primarily via exclusion of other reasons for hypogammaglobulinaemia. In this study, we aimed to retrospectively analyze the frequency and characteristics of adult patients with altered telomere maintenance (manifesting themselves as "cryptic DKC") within a well-defined cohort of patients with clinical findings of CVID.

Materials and Methods: 200 patients of the Freiburg registry of adult CVID patients underwent whole-exome sequencing (WES). Diagnosis of CVID was established based on the recommendations of the European Society of Immune Deficiencies. Retrospectively, all patients were screened for mutations/variants in the following DKC causing genes: TERT, RTEL1, DKC1, NHP2, TERC, NOP10, TCAB1, TIN2 and CTC1. Screening identified 23 patients (age: 45 +/- 13 years; mean +/- S.D.) with mutations/polymorphisms in these genes. All identified variants were heterozygous. One patient showed polymorphisms in three different genes. To analyze the functional consequences on telomere maintenance, telomere length (TL) of peripheral blood mononuclear cells (PBMCs) were analyzed via MM-Q-PCR in all 23 patients. Furthermore, Flow-FISH analysis of lymphocytes as well as granulocytes was carried out in 22 and 14 patients, respectively.

Results: TL analysis measured with MM-Q-PCR showed in most of the 23 patients shortened TL compared to an age-matched control group. We measured premature TL shortening below the 1% percentile in 44% (10/23) and below the 10% percentile in 52% (12/23). TL determined via flow-FISH showed TL in lymphocytes below the 10% percentile in 64% (14/22) and below 1% in 27% (6/22). WES revealed 24 polymorphisms/mutations in RTEL1 (n=5), TERT (n=3), NHP2 (n=6), DKC1 (n=8) and CTC1 (n=2). Based on bioinformatic prediction, 78 % (19/24) of all polymorphisms were classified as likely benign variants. Two patients with pathogenic mutations were identified: One 30 year old patient with previously described pathogenic TERT mutation (c.1234C>T, p.His412Tyr) was identified showing lymphocyte and granulocyte TL with flow-FISH between the 1% and 10% percentile and below the 1% percentile using MM-Q-PCR. One 23 year old patient with a bioinformatic predicted pathogenic mutation in RTEL1 (c.2313_2315delAGA, p.Glu771del) showed TL in flow-FISH and MM-Q-PCR below the 1% percentile. Of note, this patient developed few years after initial CVID diagnosis severe interstitial lung disease. Three patients were identified with possible DKC showing variants of unknown significance in the RTEL1 (41 years: c.380G>A, p.Arg127Gln) and TERT (65 years: c.3257G>A, p.Arg1086His and 42 years: c.1843G>A, p.Ala615Thr) gene having both TL in lymphocytes/granulocytes (flow-FISH) and leukocytes (MM-Q-PCR) below the 5% percentile.

Conclusions: Clinical signs of immunodeficiency can be a rare first manifestation of cryptic/late-onset DKC in adult patients. We found out that at least 1% of all patients with CVID syndrome is caused by mutations typically found in DKC. Our data adds a further important clinical manifestation to the broad clinical spectrum of cryptic DKC. In return, awareness of CVID as a possible first manifestation of cryptic DKC can improve patient management. TL analysis in addition to genetic work-up provides a valuable tool to identify DKC as underlying disease of CVID and other disorders characterized by impaired replicative potential.