CASE REPORT published: 12 February 2020 doi: 10.3389/fimmu.2020.00046 Uncovering Low-Level Maternal Gonosomal Mosaicism in X-Linked Agammaglobulinemia: Implications for Genetic Counseling Jacques G. Rivière 1,2 , Clara Franco-Jarava 2,3 , Mónica Martínez-Gallo 2,3 , Aina Aguiló-Cucurull 2,3 , Laura Blasco-Pérez 4 , Ida Paramonov 4 , María Antolín 4 , Andrea Martín-Nalda 1,2 , Pere Soler-Palacín 1,2 and Roger Colobran 2,3,4* 1 Pediatric Infectious Diseases and Immunodeficiencies Unit, Vall d’Hebron Research Institute, Hospital Universitari Vall d’Hebron, Universitat Autònoma de Barcelona, Barcelona, Spain, 2 Jeffrey Model Foundation Excellence Center, Barcelona, Spain, 3 Immunology Division, Department of Cell Biology, Physiology and Immunology, Vall d’Hebron Research Institute, Hospital Universitari Vall d’Hebron, Autonomous University of Barcelona, Barcelona, Spain, 4 Department of Clinical and Molecular Genetics, Hospital Universitari Vall d’Hebron, Barcelona, Spain X-linked agammaglobulinemia (XLA) is a clinically and genetically well-defined immunodeficiency and the most common form of agammaglobulinemia. It Edited by: is characterized by susceptibility to recurrent bacterial infections, profound Menno C. van Zelm, hypogammaglobulinemia, and few or no circulating B cells. XLA is caused by mutations Monash University, Australia in the BTK gene, which encodes Bruton’s tyrosine kinase (BTK). Because of its X-linked Reviewed by: Hirokazu Kanegane, recessive inheritance pattern, XLA virtually only affects males, and the mother is the Tokyo Medical and Dental carrier of the mutation in 80–85% of the males with this condition. In the remaining University, Japan 15–20% of the cases, the affected male is considered to have a de novo mutation. C. I. Edvard Smith, Karolinska Institutet (KI), Sweden Here, we present the case of a child with a diagnosis of XLA caused by a missense *Correspondence: mutation in the BTK gene (c.494G>A/p.C165Y). Apparently, his mother was wild type Roger Colobran for this gene, which implied that the mutation was de novo, but careful analysis of rcolobran@vhebron.net Sanger electropherograms and the use of high-coverage massive parallel sequencing Specialty section: revealed low-level maternal gonosomal mosaicism. The mutation was detected in This article was submitted to various samples from the mother (blood, urine, buccal swab, and vaginal swab) at a low Primary Immunodeficiencies, a section of the journal frequency of 2–5%, and the status of the patient’s mutation changed from de novo to Frontiers in Immunology inherited. This study underscores the importance of accurately establishing the parents’ Received: 02 December 2019 status on detection of an apparently de novo mutation in a patient, as inadvertent Accepted: 09 January 2020 low-level mosaicism may lead to misinterpretation of the risk of recurrence, vital for Published: 12 February 2020 genetic counseling. Citation: Rivière JG, Franco-Jarava C, Keywords: X-linked agammaglobulinemia (XLA), Bruton agammaglobulinemia, gonosomal mosaicism, genetic Martínez-Gallo M, Aguiló-Cucurull A, counseling, BTK mutation Blasco-Pérez L, Paramonov I, Antolín M, Martín-Nalda A, Soler-Palacín P and Colobran R (2020) Uncovering Low-Level INTRODUCTION Maternal Gonosomal Mosaicism in X-Linked Agammaglobulinemia: X-linked agammaglobulinemia (XLA, OMIM #300755) is a prototypical primary Implications for Genetic Counseling. immunodeficiency (PID), which was first described in 1952 by the pediatrician Ogden Carr Front. Immunol. 11:46. Bruton (1). XLA is characterized by increased susceptibility to bacterial infections, a huge doi: 10.3389/fimmu.2020.00046 reduction in all serum immunoglobulin isotypes, and a profound decrease or absence of peripheral Frontiers in Immunology | www.frontiersin.org 1 February 2020 | Volume 11 | Article 46 Rivière et al. Maternal Gonosomal Mosaicism in XLA blood B lymphocytes (typically <2%) (2, 3). The genetic defect sequencing revealed low-level, maternal gonosomal mosaicism. underlying XLA was not discovered until 1992, when two Although the frequency of the mutation was low (<5.5%) in independent groups found that it was caused by mutations in all tissues analyzed, transmission to the patient indicated that it the BTK gene, which encodes Bruton’s tyrosine kinase (BTK) was present in germ cells, a fact with important implications for (4, 5). BTK is involved in signal transduction from the B- genetic counseling. cell immunoglobulin receptor, and BTK deficiency results in a profound block of B-cell differentiation in bone marrow at METHODS early stages (6). Several studies (including patients from different countries and ethnic groups) coincide in that more than 85% Patients and Samples of males with presumed XLA have mutations in BTK (3, 7–10). Peripheral blood was obtained from the proband, and peripheral Although it is difficult to accurately define the incidence of XLA, blood, urine, and buccal and vaginal swabs were obtained from it likely varies from 1/100,000 to 1/250,000 live births. the mother. The BTK gene, located on the long arm of the X chromosome Written informed consent for the studies reported here and (Xq22.1), contains 19 exons and codes for a 659-amino acid for the publication of this case report was obtained from the protein. Since the gene was discovered, hundreds of mutations patient’s legal representatives, and a separate consent was given were reported, and most of them were compiled in the by the mother for her samples, in accordance with the procedures BTKbase: http://structure.bmc.lu.se/idbase/BTKbase/ (11). The of the ethics review board of Hospital Universitari Vall d’Hebron mutations are scattered almost uniformly throughout the gene [code: PR(AG)69/2016]. and include a variety ranging from point mutations to large gene rearrangements. Several studies focused on the molecular Sanger Sequencing analysis of large cohorts of XLA patients. Collectively, they report All exons and flanking regions of the BTK gene were sequenced in that the most common mutations are missense, followed by the patient, whereas only the exon containing the mutation was frameshift, splicing, and non-sense mutations, whereas gross sequenced in the patient’s mother. Genomic DNA was extracted deletions and mutations affecting the promoter are the least from EDTA-containing whole-blood samples using the QIAamp frequent (3, 8, 9, 12–15). The genotype–phenotype association DNA blood mini kit (Qiagen; Hilden, Germany) according to the in XLA was addressed by several groups with discrepant results, manufacturer’s instructions. A polymerase chain reaction (PCR) but overall, a strong correlation has not been established (3, technique was carried out to amplify the 19 exons of BTK and 12, 16–18). Interestingly, although XLA is considered a fully their flanking regions (primers and PCR conditions are available penetrant disorder, hypomorphic variants presenting with a leaky upon request), and purified PCR products were sequenced on phenotype (i.e., low, but not absent, immunoglobulin levels and an ABI 3100 DNA sequencer using the BigDye Terminator decreased, but not absent, B cells) also exist and may account for sequencing kit 3.1 (Applied Biosystems; Foster, VA, USA). up to 10% of the patients (19–23). Because of its X-linked recessive inheritance pattern, XLA Targeted Gene Sequencing almost exclusively affects males, with some extremely rare Samples from the patient’s mother were analyzed to establish exceptions (24), and in about 80–85% of the affected males, the the percentage of mosaicism in different specimens (peripheral mother is the carrier of the mutation (8, 25). In the remaining blood, urine, and buccal and vaginal swabs). PCR products 15–20% of the cases, the affected male is considered to carry a de containing the exon of interest were used as DNA input novo mutation, unless he has a sibling with the same mutation. In to generate libraries, which were sequenced with the MiSeq this latter situation, maternal mosaicism is strongly suspected, as platform (Illumina, San Diego, CA). the mother is an obligate carrier. However, even in families with DNA was quantified with a Qubit 2.0 Fluorometer (Thermo a sporadic patient carrying a de novo mutation (i.e., the mother Fisher Scientific, MA, USA), and 300–900 ng of DNA was apparently does not have the mutation), maternal mosaicism fragmented using NEBNext dsDNA Fragmentase (New England cannot be excluded. In current common practice, a mutation is Biolabs, Ipswich, MA) to obtain fragments of ∼200 bp. Then, considered de novo if direct sequencing by the Sanger method end repair, ligation of the adapter for Illumina, and sample detects the mutation in the patient’s peripheral blood DNA, but indexing by a small amplification were carried out using the not in that of either of the parents. However, Sanger sequencing NEBNext Ultra DNA library prep kit for Illumina and NEBNext cannot detect mutants with low allele fractions (typically <10% Multiplex Oligos for Illumina Dual Index Primers Set 1 (New of mutated alleles). Therefore, it is conceivable that parental England Biolabs, Ipswich, MA). All necessary purifications and mosaicism may be underdetected, especially when the allele size selections to recover only the fragments of interest were fraction is low (26). The use of next-generation sequencing done using AMPure XP beads (Beckman Coulter). Libraries (NGS) technologies can greatly facilitate detection of mosaicism, were quality-evaluated using QIAxcel (Qiagen) and quantified especially low-level mosaicism (27), and this is important to with a Qubit 2.0 Fluorometer. The DNA sample libraries were unambiguously classify a mutation as inherited or de novo. then mixed in equimolecular amounts and sequenced in a Here, we report on a child diagnosed with XLA caused by a MiSeq instrument (Illumina, San Diego, CA), using the 500- missense mutation in the BTK gene (c.494G>A/p.C165Y). His cycle MiSeq reagent kit v2 with a paired-end run of 2 × mother was apparently wild type for this gene, but careful analysis 251-bp reads. All procedures were performed according to the of the Sanger sequencing results and the use of massive parallel manufacturer’s instructions. Frontiers in Immunology | www.frontiersin.org 2 February 2020 | Volume 11 | Article 46 Rivière et al. Maternal Gonosomal Mosaicism in XLA Bioinformatics Analysis TABLE 1 | Immunological parameters in the study patient. The data analysis pipeline included adapter and quality trimming 8 months Age-matched reference values of the Illumina FASTQ sequences using Trimmomatic (28), and alignment to the human genome GRCh37 (hg19) using BWA- Leukocytes (×109 /L) 10.79 5.8–17.8 MEM. Low-frequency variants in BTK were called using the Neutrophils (%) ↓19.6 35–75 Pisces variant caller (29) and annotated with ANNOVAR (30). Neutrophils (×109 /L) 2.1 1.5–5 Lymphocytes (%) ↑55.1 20–50 Flow Cytometry Assessment of Lymphocytes (×109 /L) 6 3.4–9 Intracellular BTK Expression T cells CD3+ (%) 89.97 50–77 Peripheral whole blood was collected in vacutainer tubes CD3+ (×109 /L) 4.56 2.4–6.9 containing ethylene-diamine-tetra-acetic acid (EDTA) as CD4+ (%) 55.95 33–58 anticoagulant (BD-Plymouth, PL6 7BP, UK). A 50-ml amount CD4+ (×109 /L) 2.84 1.4–5.1 of blood was incubated with a mix of specific conjugated CD8+ (%) 31.82 13–26 monoclonal antibodies (CD14–PB and CD19–PCy7). Cells were CD8+ (×109 /L) 1.61 0.6–2.2 then fixed and permeabilized according to the manufacturer’s Index 1.76 1.6–3.8 instructions for the PerFix-nc Kit (Beckman Coulter). After CD19+ (%) ↓1 13–35 permeabilization, samples were stained with anti-BTK–PE or CD19+ (×109 /L) ↓0.05 0.7–2.5 isotype control IgG1–PE (MiltenyiBiotec) and gently mixed CD56+ CD16+ (%) 5.78 2–13 for 30 min at room temperature (RT) in the dark. Samples CD56+ CD16+ (×109 /L) 0.29 0.1–1.0 were treated with 1 ml of lysing solution (VersaLyse, Beckman IgG (mg/dl) ↓135 196–1,045 Coulter), vortexed, and incubated for 15 min at RT in the IgA (mg/dl) ↓ <10 8–90 dark, and then washed with phosphate-buffered saline (PBS), IgM (mg/dl) ↓12 40–140 stored at RT in the dark, and analyzed within 1 h. Samples were acquired with a Navios EX flow cytometer (Beckman Coulter) and analyzed with Kaluza software. mutation, located in exon 6 of BTK, was classified as likely RESULTS pathogenic according to the American College of Medical Genetics and Genomics rules (31). The mutation was not found Case Presentation in the ExAC or Gnomad database, but it had been previously An 8-month-old boy was referred to our hospital for respiratory reported in a family including two boys with XLA (32). Therefore, distress, fever, and fatigue. He had been born at term from we considered BTK p.C165Y to be the causal mutation of XLA in a non-consanguineous family with no relevant prior family our patient. history. Before this episode, he had been admitted twice for We also sequenced the mother’s DNA, and she was, bronchitis at 3 and 6 months of age. During one of these episodes, apparently, wild type. However, careful analysis of the Sanger he showed severe neutropenia and received a broad-spectrum chromatogram (forward sequence) revealed a very small adenine antibiotic. Neutrophil counts fully recovered a few days later peak at the c.494 position, which would correspond to the without further treatment. On physical examination, there were mutated allele (Figure 1). Analysis of the reverse sequence no palpable lymph nodes or tonsillar tissue. Lung auscultation showed a barely visible peak at c.494, which would also detected bilateral crackles and diminished breath sounds. The correspond to the mutated allele (Figure 1). To rule out chest X-ray showed bilateral infiltrates with no pleural effusion, selective allele amplification, we designed a second pair of thus establishing the diagnosis of acute bilateral pneumonia. primers to amplify and sequence the BTK region of the Complete blood count at the age of 8 months was normal. c.494G>A/p.C165Y mutation in the mother. The results were Immunoglobulin levels were very low (IgA <10 mg/dl, IgM exactly the same, strongly suggesting the presence of maternal 12 mg/dl, and IgG 135 mg/dl) (Table 1). The patient had a gonosomal mosaicism (Figure 1). To address this issue and to clear X-linked agammaglobulinemia (XLA) immunophenotype, quantify to what extent the mutation was present in the mother, with normal T- and NK-cell numbers, and profound B-cell we performed targeted deep sequencing of the p.C165Y BTK deficiency (1%, 50 cells/µl). The lymphocyte proliferation assay mutation using DNA from hematological and non-hematological was normal. These laboratory findings, together with the absence samples. We obtained high, on-target depth coverage (from of lymph nodes and tonsils, suggested the diagnosis of XLA, and 2,454× to 107,374×), and we detected the BTK p.C165Y immunoglobulin replacement therapy was started. mutation in all samples analyzed, at similar low frequencies: blood (5.4%), urine (4.6%), buccal swab (2.3%), and vaginal swab Identification of the BTK p.C165Y Mutation (4.7%) (Figure 1). in the Patient and His Mother: Germinal Mutation vs. Gonosomal Mosaicism Flow Cytometry Assessment of Based on the clear suspicion of XLA, Sanger sequencing of Intracellular BTK Expression the BTK gene was performed, and the hemizygous missense BTK protein expression in monocytes and B cells of the patient mutation c.494G>A/p.C165Y was identified (Figure 1). This and his mother was analyzed by flow cytometry. The patient’s Frontiers in Immunology | www.frontiersin.org 3 February 2020 | Volume 11 | Article 46 Rivière et al. Maternal Gonosomal Mosaicism in XLA FIGURE 1 | Identification of the BTK mutation in the patient (germinal mutation) and his mother (gonosomal mosaicism). (Top) Diagram of the BTK gene, indicating the c.494G>A/p.C165Y mutation in exon 6. (Left) Electropherograms of Sanger sequences from the patient and his mother. In the mother, two different primer pairs were used, which consistently showed a very small peak corresponding to the mutated allele in both the sense and antisense strands. (Right) Massive parallel sequencing results for detection of the mutation in various samples from the mother. The total coverage, reads containing each allele, and percentage of the mutated allele are indicated for each sample. monocytes showed an absence of BTK expression, confirming Depending on the developmental stage in which a mutation that the p.C165Y mutation led to complete BTK deficiency occurs, mosaicism can be classified into one of three categories: (Figure 2). BTK expression in the patients’ mother was within (1) germline mosaicism (also known as gonadal mosaicism) the normal range in both monocytes and B cells, indicating refers to genetic variation emerging in cells that develop into that her low-level mosaicism did not have a significant impact gonads (ovaries and testicles). It is one cause of de novo variation and could not be reliably detected by flow cytometry (Figure 2). in the next generation; (2) somatic mosaicism, affecting cells It is difficult to establish whether the slight decrease in BTK other than germline cells; and (3) gonosomal mosaicism, a expression observed in the mother was caused by her mosaicism, combination of germline and somatic mosaicism that refers to as it was not consistently observed using other healthy controls mosaic variants present in both somatic and germline lineages (data not shown). In fact, her low-level mosaicism (∼5%) is (34, 35). below the interindividual variation of BTK expression in healthy In relation to PID, mosaicism was recently reported as controls, and this may mask its effect. an unexpectedly frequent phenomenon in patients with autoinflammatory disorders (36–39). An example of this is DISCUSSION the striking estimate that 0.5–19% of patients with cryopyrin- associated periodic syndromes (CAPS) show mosaicism (40). Mosaicism is a type of post-zygotic variation, in which two In PIDs other than autoinflammatory disorders, mosaicism or more genotypically distinct cell lines derived from a single was found to a lesser extent. Perhaps the most widely known zygote are present in an individual. Although mosaicism is and classic example was provided in 2004 by Holzelova increasingly recognized as a source of genetic variation, it is et al., who described a group of patients with autoimmune still an underestimated genetic phenomenon responsible for the lymphoproliferative syndrome (ALPS) showing somatic development of human phenotypes in health and disease (33). mosaicism and heterozygous FAS mutations in polyclonal Frontiers in Immunology | www.frontiersin.org 4 February 2020 | Volume 11 | Article 46 Rivière et al. Maternal Gonosomal Mosaicism in XLA FIGURE 2 | Flow cytometry assessment of intracellular BTK expression. BTK protein expression is shown in the patient, his mother, and a healthy control. Monocytes and B cells were both examined. In the patient, only monocytes were analyzed due to the lack of B cells. The results are shown individually and grouped for easy comparison. double-negative T cells (41). Later, other groups confirmed and to be an obligate carrier (44–47). For example, in 2001, extended this finding, reporting that somatic mutations account Sakamoto et al. described two XLA brothers with the same for up to 15% of ALPS cases (42). Only very recently has the role BTK mutation, born of a mother with no evidence of the of gene mosaicism in PID patients been extensively investigated. mutation. The authors Sanger sequenced the BTK gene in In a study led by JI Arostegui including 92 families with a single the blood samples and buccal mucosal cells from the mother, member carrying a presumably de novo mutation, six families and no mutations were detected. The fact that a non-carrier (6.5%) were identified in which one parent carried the mutation mother had two affected sons with the same mutation led the in the form of gonosomal mosaicism (43). These results also authors to suggest maternal gonadal mosaicism (44). A recent support the notion that this phenomenon is remarkably frequent study by Segundo et al. reported a case of XLA in which the in patients with autoinflammatory diseases (43). patient and his daughter carried the same BTK mutation, but In XLA, around 15–20% of the patients were considered the mother had no mutations in BTK, findings that strongly to have de novo mutations because the mother was not a suggest maternal gonadal (or gonosomal) mosaicism. In this carrier, as typically determined by the Sanger method. However, case, the authors only sequenced BTK from blood DNA (Sanger a presumed de novo mutation may, in fact, be inherited by method) and did not investigate mosaicism in the mother undetected mosaicism in a parent who lacks symptoms. Since (45). To date, the only study that has fully demonstrated the discovery of BTK as the genetic defect underlying XLA parental mosaicism in XLA is the aforementioned report by JI (4, 5), several studies pointed out that parental mosaicism had Arostegui, in which BTK gonosomal mosaicism was found in to be present in some cases where a parent was expected two unrelated families with XLA patients (43). These authors Frontiers in Immunology | www.frontiersin.org 5 February 2020 | Volume 11 | Article 46 Rivière et al. Maternal Gonosomal Mosaicism in XLA demonstrated mosaicism in DNA from the mothers’ whole blood DATA AVAILABILITY STATEMENT samples using NGS, but they did not investigate DNA from other tissues. The raw data supporting the conclusions of this article will be To our knowledge, the present study is the first to made available by the authors, without undue reservation, to any comprehensively report low-level maternal gonosomal qualified researcher. mosaicism in XLA with evidence from DNA analysis of various tissues. We found that the low-level mosaicism detected in the ETHICS STATEMENT mother’s blood (5.4% of NGS reads) was consistently present at a similar frequency in the other samples analyzed (urine, Written informed consent for the studies reported here and for and buccal and vaginal swab). Detection and quantification of the publication of this case report was obtained from the patient’s mosaicism is important for establishing the diagnosis of disease, legal representatives, and a separate consent was given by the assessing the risk of recurrence, and guiding genetic counseling. mother for her samples, in accordance with the procedures of NGS is a proven, reliable technique to identify low-level the Ethics Review Board of Hospital Universitari Vall d’Hebron mosaicism, which may go undetected by conventional Sanger [code: PR(AG)69/2016]. sequencing (27). This is crucial when addressing the parent’s status for a previously identified mutation because the presence AUTHOR CONTRIBUTIONS of inadvertent low-level mosaicism may lead to misinterpretation of a genetic testing result. In particular, an inherited case may be JR was the principal clinician in charge of the patient’s care. misinterpreted as de novo due to low-level mosaicism in a carrier He collected clinical data and wrote part of the manuscript. parent. In addition, estimation of the risk of recurrence can be CF-J participated in the study design and collected laboratory highly inaccurate when mosaicism is not considered during data. MM-G performed the flow cytometry analysis. AA-C genetic counseling (48). In the mothers of XLA patients with provided technical support for sample collection and the Sanger germline BTK mutations, the probability of recurrence would sequencing process. LB-P, IP, and MA performed the massive be ∼50%, whereas in true de novo mutations, the risk would parallel sequencing and data analysis. AM-N and PS-P were be the same as in the general population (negligible in terms of clinicians in charge of patient care and management. RC was genetic counseling). In XLA patients with a mosaic parent, it can responsible for designing the study, performing the genetic be assumed that the recurrence risk would be dependent on the analysis, writing the manuscript, and approving the final draft. percentage of germ cell progenitors that harbor the mutation All authors reviewed the manuscript and contributed to the (49). In malesDNA analysis in sperm can be informative for risk final draft. assessment, but in a woman, the level of mosaicism in gonads cannot be easily determined (50). In our patient’s mother, the FUNDING mutation was detected at a similar low frequency (≤5.5%) in all tissues analyzed, which represented the three germ layers This study was funded by Instituto de Salud Carlos III (ectoderm, endoderm, and mesoderm). Although it is tempting grants PI14/00405 and PI17/00660, cofinanced by the European to speculate that the results would be similar in gonads, this Regional Development Fund (ERDF). This study was also funded assumption cannot be made, as the level of mosaicism varies by the Jeffrey Modell Foundation (JMF). substantially between different tissues and body locations, even within the same embryonic lineage (50). In the light of these ACKNOWLEDGMENTS considerations, a precise estimation of recurrence risk is difficult in the case reported here. At present, a conservative approach has We are deeply grateful to the affected individual and his family been followed, offering by default the same risk as in germline who generously participated in this study. We acknowledge BTK mutations (up to 50%). Celine Cavallo for English language support. REFERENCES in human X-linked agammaglobulinemia. Cell. (1993) 72:279–90. doi: 10.1016/0092-8674(93)90667-F 1. Bruton OC. Agammaglobulinemia. Pediatrics. (1952) 9:722–8. 6. Maas A, Hendriks RW. Role of Bruton’s tyrosine kinase in B cell development. 2. Conley ME, Rohrer J, Minegishi Y. X-linked agammaglobulinemia. 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Linkage analysis and physical mapping near the gene for X-linked agammaglobulinemia at Xq22. Genomics. (1993) 15:342–9. Conflict of Interest: The authors declare that the research was conducted in the doi: 10.1006/geno.1993.1066 absence of any commercial or financial relationships that could be construed as a 47. Jo EK, Kanegane H, Nonoyama S, Tsukada S, Lee JH, Lim K, et al. potential conflict of interest. Characterization of mutations, including a novel regulatory defect in the first intron, in Bruton’s tyrosine kinase gene from seven Korean Copyright © 2020 Rivière, Franco-Jarava, Martínez-Gallo, Aguiló-Cucurull, X-linked agammaglobulinemia families. J Immunol. (2001) 167:4038–45. Blasco-Pérez, Paramonov, Antolín, Martín-Nalda, Soler-Palacín and Colobran. doi: 10.4049/jimmunol.167.7.4038 This is an open-access article distributed under the terms of the Creative 48. Campbell IM, Yuan B, Robberecht C, Pfundt R, Szafranski P, McEntagart Commons Attribution License (CC BY). The use, distribution or reproduction ME, et al. Parental somatic mosaicism is underrecognized and influences in other forums is permitted, provided the original author(s) and the recurrence risk of genomic disorders. Am J Hum Genet. (2014) 95:173–82. copyright owner(s) are credited and that the original publication in this doi: 10.1016/j.ajhg.2014.07.003 journal is cited, in accordance with accepted academic practice. No use, 49. Biesecker LG, Spinner NB. A genomic view of mosaicism and human disease. distribution or reproduction is permitted which does not comply with these Nat Rev Genet. (2013) 14:307–20. doi: 10.1038/nrg3424 terms. Frontiers in Immunology | www.frontiersin.org 8 February 2020 | Volume 11 | Article 46