Detecting 22q11.2 Deletion Syndrome in Newborns with Low T Cell Receptor Excision Circles from Severe Combined Immunodeficiency Screening

Chromosome 22q11.2 Deletion (DiGeorge Syndrome): Immunologic Features, Diagnosis, and Management

PURPOSE OF REVIEW

This review focuses on immunologic findings, relationships among immunologic findings and associated conditions of autoimmunity and atopy, and management of immunologic disease in chromosome 22q11.2 deletion syndrome (22q11.2DS, historically known as DiGeorge syndrome).

RECENT FINDINGS

The implementation of assessment of T cell receptor excision circles (TRECs) in newborn screening has led to increased detection of 22q11.2 deletion syndrome. While not yet applied in clinical practice, cell-free DNA screening for 22q11.2DS also has the potential to improve early detection, which may benefit prompt evaluation and management. Multiple studies have further elucidated phenotypic features and potential biomarkers associated with immunologic outcomes, including the development of autoimmune disease and atopy. The clinical presentation of 22q11.2DS is highly variable particularly with respect to immunologic manifestations. Time to recovery of immune system abnormalities is not well-defined in current literature. An understanding of the underlying causes of immunologic changes found in 22q11.2DS, and the progression and evolution of immunologic changes over the lifespan have expanded over time and with improved survival. An included case highlights the variability of presentation and potential severity of T cell lymphopenia in partial DiGeorge syndrome and demonstrates successful spontaneous immune reconstitution in partial DiGeorge syndrome despite initial severe T cell lymphopenia.

Human thymus in health and disease: Recent advances in diagnosis and biology

The thymus is the crucial tissue where thymocytes develop from hematopoietic precursors that originate from the bone marrow and differentiate to generate a repertoire of mature T cells able to respond to foreign antigens while remaining tolerant to self-antigens. Until recently, most of the knowledge on thymus biology and its cellular and molecular complexity have been obtained through studies in animal models, because of the difficulty to gain access to thymic tissue in humans and the lack of in vitro models able to faithfully recapitulate the thymic microenvironment. This review focuses on recent advances in the understanding of human thymus biology in health and disease obtained through the use of innovative experimental techniques (eg. single cell RNA sequencing, scRNAseq), diagnostic tools (eg. next generation sequencing), and in vitro models of T-cell differentiation (artificial thymic organoids) and thymus development (eg. thymic epithelial cell differentiation from embryonic stem cells or induced pluripotent stem cells).

Fever of Unknown Origin Reveals a Missed Diagnosis of DiGeorge Syndrome in a 21-Year-Old Female

DiGeorge syndrome, caused by a microdeletion of the 22q11.2 region of chromosome 22, is a relatively rare condition. This syndrome can be difficult to recognize because a constellation of symptoms show different presentations. Most individuals diagnosed with this condition are identified in early childhood. With the emergence of new screening techniques, even fewer individuals with this syndrome are missed. Prior to these screening techniques, it was uncommon for patients to be diagnosed in adulthood. As a result, many internists, who focus only on the adult population, are unlikely to recognize and diagnose DiGeorge syndrome as the patient ages merely because it is not commonly diagnosed later in life. Early recognition and management are essential for the treatment of this condition. Here, we present the case of a 21-year-old woman diagnosed with DiGeorge syndrome as an adult.

Screening Method for 22q11 Deletion Syndrome Involving the Use of TaqMan qPCR for TBX1 in Patients with Conotruncal Congenital Heart Disease

22q11.2 deletion syndrome is a phenotypic spectrum that encompasses DiGeorge syndrome (OMIM: 188400) and velocardiofacial syndrome (OMIM: 192430). It is caused by a 1.5–3.0 Mb hemizygous deletion of locus 22q11.2, which leads to characteristic facies, conotruncal cardiovascular malformations, velopharyngeal insufficiency, T-lymphocyte dysfunction due to thymic aplasia, and parathyroid hypoplasia, and, less frequently, neurological manifestations such as delayed psychomotor development or schizophrenia. This study aimed to describe a screening method for the diagnosis of 22q11.2 deletion syndrome in patients with Conotruncal Congenital Heart Disease (CCHD), using qPCR to detect the copy number of the TBX1 gene in a single DNA sample. A total of 23 patients were included; 21 with a biallelic prediction of the TBX1 copy number gene and 2 with a monoallelic prediction who were suspected to be positive and subjected to MLPA confirmation. One patient (4.34%) with truncus arteriosus CCHD was confirmed to have 22q11.2 deletion syndrome. We propose this approach as a possible newborn screening method for 22q11.2 deletion syndrome in CCHD patients.

Long-Term Follow-Up of Newborns with 22q11 Deletion Syndrome and Low TRECs

Background

Population-based neonatal screening using T-cell receptor excision circles (TRECs) identifies infants with profound T lymphopenia, as seen in cases of severe combined immunodeficiency, and in a subgroup of infants with 22q11 deletion syndrome (22q11DS).

Purpose

To investigate the long-term prognostic value of low levels of TRECs in newborns with 22q11DS.

Methods

Subjects with 22q11DS and low TRECs at birth (22q11Low, N=10), matched subjects with 22q11DS and normal TRECs (22q11Normal, N=10), and matched healthy controls (HC, N=10) were identified. At follow-up (median age 16 years), clinical and immunological characterizations, covering lymphocyte subsets, immunoglobulins, TRECs, T-cell receptor repertoires, and relative telomere length (RTL) measurements were performed.

Results

At follow-up, the 22q11Low group had lower numbers of naïve T-helper cells, naïve T-regulatory cells, naïve cytotoxic T cells, and persistently lower TRECs compared to healthy controls. Receptor repertoires showed skewed V-gene usage for naïve T-helper cells, whereas for naïve cytotoxic T cells, shorter RTL and a trend towards higher clonality were found. Multivariate discriminant analysis revealed a clear distinction between the three groups and a skewing towards Th17 differentiation of T-helper cells, particularly in the 22q11Low individuals. Perturbations of B-cell subsets were found in both the 22q11Low and 22q11Normal group compared to the HC group, with larger proportions of naïve B cells and lower levels of memory B cells, including switched memory B cells.

Conclusions

This long-term follow-up study shows that 22q11Low individuals have persistent immunologic aberrations and increased risk for immune dysregulation, indicating the necessity of lifelong monitoring.

Clinical Implications

This study elucidates the natural history of childhood immune function in newborns with 22q11DS and low TRECs, which may facilitate the development of programs for long-term monitoring and therapeutic choices.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10875-021-01201-5.

Clinical Features in a Large Cohort of Patients With 22q11.2 Deletion Syndrome

OBJECTIVES

To evaluate various clinical aspects, specifically regarding immune status, in a large cohort of patients with DiGeorge syndrome.

STUDY DESIGN

Data were collected for 98 patients with DiGeorge syndrome treated at a tertiary medical center. This included general information, laboratory results, and clinical features.

RESULTS

The median age at diagnosis was 2.0 years (range, 0.0-36.5 years). The most common symptoms that led to diagnosis were congenital heart defect, speech delay, palate anomalies, and developmental delay. Common clinical features included recurrent infections (76 patients), congenital heart diseases (61 patients), and otorhinolaryngology disorders (61 patients). Twenty patients had anemia; the incidence was relatively high among patients aged 6-59 months. Thrombocytopenia was present in 20 patients. Recurrent chest infections were significantly higher in patients with T cell and T cell subset deficiencies. Decreased T cell receptor excision circles were more common with increasing age (P < .001). Of the 27 patients hospitalized due to infection, pneumonia was a leading cause in 13.

CONCLUSIONS

Awareness of DiGeorge syndrome's typical and uncommon characteristics is important to improve diagnosis, treatment, surveillance, and follow-up.

Nonsevere combined immunodeficiency T-cell lymphopenia identified through newborn screening

PURPOSE OF REVIEW

Although severe combined immunodeficiency (SCID) is the primary target condition for newborn screening (NBS), over 25 secondary targets, conditions other than SCID, have been identified. There is no standard method for evaluating neonates with non-SCID T-cell lymphopenia (TCL) and no standard approaches to treatment. We will describe these conditions and discuss recommendations for evaluating and follow-up of non-SCID TCL detected by NBS.

RECENT FINDINGS

The birth prevalence of non-SCID TCL detected through SCID NBS is higher than SCID and can be a burden on NBS programs. We will present some publications discussing outcomes and comorbidities in these patients.

SUMMARY

NBS for SCID has been very successful in identifying infants with SCID at birth to institute early life saving therapies. TCL due to other conditions can cause significant immune deficiency and treatment is dependent on the cause of the defect, as well as the magnitude of the immunodeficiency. Data collection from NBS programs should include assessment of various therapies and clinical outcomes. Better systems for recording long-term outcomes of SCID NBS including both SCID and non-SCID conditions should become a priority for NBS programs. This will help to advance the goal of NBS programs: improve outcomes in the most cost-effective manner.

Establishing Simultaneous T Cell Receptor Excision Circles (TREC) and K-Deleting Recombination Excision Circles (KREC) Quantification Assays and Laboratory Reference Intervals in Healthy Individuals of Different Age Groups in Hong Kong

The clinical experience gathered throughout the years has raised awareness of primary immunodeficiency diseases (PIDD). T cell receptor excision circles (TREC) and kappa-deleting recombination excision circles (KREC) assays for thymic and bone marrow outputs measurement have been widely implemented in newborn screening (NBS) programs for Severe Combined Immunodeficiency. The potential applications of combined TREC and KREC assay in PIDD diagnosis and immune reconstitution monitoring in non-neonatal patients have been suggested. Given that ethnicity, gender, and age can contribute to variations in immunity, defining the reference intervals of TREC and KREC levels in the local population is crucial for setting up cut-offs for PIDD diagnosis. In this retrospective study, 479 healthy Chinese sibling donors (240 males and 239 females; age range: 1 month-74 years) from Hong Kong were tested for TREC and KREC levels using a simultaneous quantitative real-time PCR assay. Age-specific 5th-95th percentile reference intervals of TREC and KREC levels (expressed in copies per μL blood and copies per 106 cells) were established in both pediatric and adult age groups. Significant inverse correlations between age and both TREC and KREC levels were observed in the pediatric age group. A significant higher KREC level was observed in females than males after 9-12 years of age but not for TREC. Low TREC or KREC levels were detected in patients diagnosed with mild or severe PIDD. This assay with the established local reference intervals would allow accurate diagnosis of PIDD, and potentially monitoring immune reconstitution following haematopoietic stem cell transplantation or highly active anti-retroviral therapy in the future.