Two Unique Cases of X-linked SCID: A Diagnostic Challenge in the Era of Newborn Screening.

In the era of newborn screening (NBS) for severe combined immunodeficiency (SCID) and the possibility of gene therapy (GT), it is important to link SCID phenotype to the underlying genetic disease. In western countries, X-linked interleukin 2 receptor gamma chain (IL2RG) and adenosine deaminase (ADA) deficiency SCID are two of the most common types of SCID and can be treated by GT. As a challenge, both IL2RG and ADA genes are highly polymorphic and a gene-based diagnosis may be difficult if the variant is of unknown significance or if it is located in non-coding areas of the genes that are not routinely evaluated with exon-based genetic testing (e.g., introns, promoters, and the 5'and 3' untranslated regions). Therefore, it is important to extend evaluation to non-coding areas of a SCID gene if the exon-based sequencing is inconclusive and there is strong suspicion that a variant in that gene is the cause for disease. Functional studies are often required in these cases to confirm a pathogenic variant. We present here two unique examples of X-linked SCID with variable immune phenotypes, where IL2R gamma chain expression was detected and no pathogenic variant was identified on initial genetic testing. Pathogenic IL2RG variants were subsequently confirmed by functional assay of gamma chain signaling and maternal X-inactivation studies. We propose that such tests can facilitate confirmation of suspected cases of X-linked SCID in newborns when initial genetic testing is inconclusive. Early identification of pathogenic IL2RG variants is especially important to ensure eligibility for gene therapy.

Case Definitions for Conditions Identified by Newborn Screening Public Health Surveillance.

Newborn screening (NBS) identifies infants with rare conditions to prevent death or the onset of irreversible morbidities. Conditions on the Health and Human Services Secretary's Recommended Uniform Screening Panel have been adopted by most state NBS programs, providing a consistent approach for identification of affected newborns across the United States. Screen-positive newborns are identified and referred for confirmatory diagnosis and follow-up. The designation of a clinically significant phenotype precursor to a clinical diagnosis may vary between clinical specialists, resulting in diagnostic variation. Determination of disease burden and birth prevalence of the screened conditions by public health tracking is made challenging by these variations. This report describes the development of a core group of new case definitions, along with implications, plans for their use, and links to the definitions that were developed by panels of clinical experts. These definitions have been developed through an iterative process and are piloted in NBS programs. Consensus public health surveillance case definitions for newborn screened disorders will allow for consistent categorization and tracking of short- and long-term follow-up of identified newborns at the local, regional, and national levels.

Modeling altered T-cell development with induced pluripotent stem cells from patients with RAG1-dependent immune deficiencies.

Primary immunodeficiency diseases comprise a group of heterogeneous genetic defects that affect immune system development and/or function. Here we use in vitro differentiation of human induced pluripotent stem cells (iPSCs) generated from patients with different recombination-activating gene 1 (RAG1) mutations to assess T-cell development and T-cell receptor (TCR) V(D)J recombination. RAG1-mutants from severe combined immunodeficient (SCID) patient cells showed a failure to sustain progression beyond the CD3(--)CD4(-)CD8(-)CD7(+)CD5(+)CD38(-)CD31(-/lo)CD45RA(+) stage of T-cell development to reach the CD3(-/+)CD4(+)CD8(+)CD7(+)CD5(+)CD38(+)CD31(+)CD45RA(-) stage. Despite residual mutant RAG1 recombination activity from an Omenn syndrome (OS) patient, similar impaired T-cell differentiation was observed, due to increased single-strand DNA breaks that likely occur due to heterodimers consisting of both an N-terminal truncated and a catalytically dead RAG1. Furthermore, deep-sequencing analysis of TCR-ß (TRB) and TCR-α (TRA) rearrangements of CD3(-)CD4(+)CD8(-) immature single-positive and CD3(+)CD4(+)CD8(+) double-positive cells showed severe restriction of repertoire diversity with preferential usage of few Variable, Diversity, and Joining genes, and skewed length distribution of the TRB and TRA complementary determining region 3 sequences from SCID and OS iPSC-derived cells, whereas control iPSCs yielded T-cell progenitors with a broadly diversified repertoire. Finally, no TRA/δ excision circles (TRECs), a marker of TRA/δ locus rearrangements, were detected in SCID and OS-derived T-lineage cells, consistent with a pre-TCR block in T-cell development. This study compares human T-cell development of SCID vs OS patients, and elucidates important differences that help to explain the wide range of immunologic phenotypes that result from different mutations within the same gene of various patients.

Parental permission for pilot newborn screening research: guidelines from the NBSTRN.

There is broad recognition of the need for population-based research to assess the safety and efficacy of newborn screening (NBS) for conditions that are not on current panels. However, prospective population-based research poses significant ethical, regulatory, and logistical challenges. In the context of NBS, there have been a variety of approaches that address parental decision-making in pilot studies of new screening tests or conditions. This article presents an ethical and legal analysis of the role of parental permission by the Bioethics and Legal Work Group of the Newborn Screening Translational Research Network created under a contract from the National Institute of Child Health and Human Development to the American College of Medical Genetics and Genomics. Circumstances are outlined in which a waiver of documentation of permission or a waiver of permission may be ethically and legally appropriate in the NBS context. These guidelines do not constitute American Academy of Pediatrics policy.

Decision-making process for conditions nominated to the recommended uniform screening panel: statement of the US Department of Health and Human Services Secretary's Advisory Committee on Heritable Disorders in Newborns and Children.

PURPOSE: The US Secretary of Health and Human Services provides guidance to state newborn screening programs about which conditions should be included in screening (i.e., the "Recommended Uniform Screening Panel"). This guidance is informed by evidence-based recommendations from the Secretary's Advisory Committee on Heritable Disorders in Newborns and Children. This report describes the Advisory Committee's revised decision-making process for considering conditions nominated to the panel. METHODS: An expert panel meeting was held in April 2012 to revise the decision matrix, which helps to guide the recommendation process. In January 2013, the Advisory Committee voted to adopt the revised decision matrix. RESULTS: The revised decision matrix clarifies the approach to rating magnitude and certainty of the net benefit of screening to the population of screened newborns for nominated conditions, and now includes the consideration of the capability of state newborn screening programs for population-wide implementation by evaluating the feasibility and readiness of states to adopt screening for nominated conditions. CONCLUSION: The revised decision matrix will bring increased quality, transparency, and consistency to the process of modifying the recommended uniform screening panel and will now allow formal evaluation of the challenges that state newborn screening programs face in adopting screening for new conditions.