Prenatal diagnosis of RAG-deficient Omenn syndrome

Identification of patients with RAG mutations previously diagnosed with common variable immunodeficiency disorders

PURPOSE

Combined immunodeficiency (CID) presents a unique challenge to clinicians. Two patients presented with the prior clinical diagnosis of common variable immunodeficiency (CVID) disorder marked by an early age of presentation, opportunistic infections, and persistent lymphopenia. Due to the presence of atypical clinical features, next generation sequencing was applied documenting RAG deficiency in both patients.

METHODS

Two different genetic analysis techniques were applied in these patients including whole exome sequencing in one patient and the use of a gene panel designed to target genes known to cause primary immunodeficiency disorders (PIDD) in a second patient. Sanger dideoxy sequencing was used to confirm RAG1 mutations in both patients.

RESULTS

Two young adults with a history of recurrent bacterial sinopulmonary infections, viral infections, and autoimmune disease as well as progressive hypogammaglobulinemia, abnormal antibody responses, lymphopenia and a prior diagnosis of CVID disorder were evaluated. Compound heterozygous mutations in RAG1 (1) c256_257delAA, p86VfsX32 and (2) c1835A>G, pH612R were documented in one patient. Compound heterozygous mutations in RAG1 (1) c.1566G>T, p.W522C and (2) c.2689C>T, p. R897X) were documented in a second patient post-mortem following a fatal opportunistic infection.

CONCLUSION

Astute clinical judgment in the evaluation of patients with PIDD is necessary. Atypical clinical findings such as early onset, granulomatous disease, or opportunistic infections should support the consideration of atypical forms of late onset CID secondary to RAG deficiency. Next generation sequencing approaches provide powerful tools in the investigation of these patients and may expedite definitive treatments.

Severe combined immunodeficiency in Serbia and Montenegro between years 1986 and 2010: a single-center experience

Severe combined immunodeficiency (SCID), including the 'variant' Omenn syndrome (OS), represent a heterogeneous group of monogenic disorders characterized by defect in differentiation of T- and/or B lymphocytes and susceptibility to infections since birth. In the period of 25 years, between January 1986 and December 2010, a total of 21 patients (15 SCID, 6 OS) were diagnosed in Mother & Child Health Institute of Serbia, a tertiary-care teaching University hospital and a national referral center for patients affected with primary immunodeficiency (PID). The diagnoses were based on anamnestic data, clinical findings, and immunological and genetic analysis. The median age at the onset of the first infection was the 2nd month of life. Seven (33 %) patients had positive family history for SCID. Out of five male infants with T-B+NK- SCID phenotype, mutation analysis revealed interleukin-2 (common) gamma-chain receptor (IL2RG) mutations in 3 with positive X-linked family history, and Janus-kinase (JAK)-3 gene defects in the other two. Six patients had T-B-NK+ SCID phenotype and further 6 features of OS, 11 of which had recombinase-activating gene (RAG1or RAG2) and 1 Artemis gene mutations. One child with T+B+NK+ SCID phenotype as well had proven RAG mutation. One child each with T-B+NK+ SCID phenotype, CD8 lymphopenia and unknown phenotype remained without known underlying genetic defect. Of the eight patients who underwent hematopoetic stem cell transplant (HSCT) 5 survived, the other 13 died between 2 days and 12 months after diagnosis was made. Early diagnosis of SCID, before onset of severe infections, offers possibility for HSCT and cure. Education of primary-care pediatricians, in particular including awareness of the risk of using live vaccines and non-irradiated blood products, should improve prognosis of SCID in our setting.

Cancer genetic testing and assisted reproduction

PURPOSE

Because of increasing uptake of cancer genetic testing and the improving survival of young patients with cancer, health care practitioners including oncologists will increasingly be asked about options for assisted reproduction by members of families affected by hereditary cancer syndromes. Among these reproductive options, preimplantation genetic diagnosis (PGD) offers the opportunity to select embryos without familial cancer-predisposing mutations.

METHODS

A review of the published literature supplemented by a survey of PGD centers in the United States.

RESULTS

Prenatal diagnosis and/or embryo selection after genetic testing has already been performed in the context of more than a dozen familial cancer syndromes, including the common syndromes of genetic predisposition to colon and breast cancer.

CONCLUSION

While constituting new reproductive options for families affected by cancer, the medical indications and ethical acceptance of assisted reproductive technologies for adult-onset cancer predisposition syndromes remain to be defined. Continued discussion of the role of PGD in the reproductive setting is needed to inform the responsible use of these technologies to decrease the burden of heritable cancers.

Detection of RAG mutations and prenatal diagnosis in families presenting with either T-B- severe combined immunodeficiency or Omenn's syndrome

It has been recently shown that mutations in both of the recombination activating genes RAG1 and RAG2 are involved in each of the two different types of severe combined immunodeficiency (SCID) syndromes: T-B- SCID and Omenn's syndrome (OS). The objective of the study was to search for novel mutations in the RAG genes and to offer prenatal diagnosis for families that have been identified as at risk of T-B- SCID or OS. Mutation analyses of polymerase chain reaction products of RAG1/RAG2 genes were performed in 14 cases (T-B- SCID = 6 and OS = 8). Consanguinity was reported in seven (50%) families. Four missense mutations in the RAG2 gene in six of eight OS patients and in four of six T-B- SCID patients were detected. The C1845T transition leading to a Tre215Ile substitution is a novel mutation. All but one of the patients were homozygous for the detected mutations, possibly reflecting the consanguinity in these families and the relative rarity of the disease-causing mutations. In addition, three putative polymorphic sites were found. Prenatal diagnosis was offered to seven families, but three of them declined genetic counseling for religious reasons. In the remaining families, four pregnancies were successfully completed, and in one case, the family chose to have an abortion because of a homozygous mutation. Mutations in RAG1/RAG2 genes were detected in only some of the T-B- SCID or OS patients, and the molecular basis for the remaining cases has yet to be elucidated. Important factors such as religious beliefs need to be considered when offering prenatal diagnosis to certain families.

Mutations in genes required for T-cell development:IL7R, CD45, IL2RG, JAK3, RAG1, RAG2, ARTEMIS, and ADA and severe combined immunodeficiency: HuGE review

Severe combined immunodeficiency (SCID) is an inherited immune disorder characterized by T-cell lymphopenia (TCLP), a profound lack of cellular (T-cell) and humoral (B-cell) immunity and, in some cases, decreased NK-cell number and function. Affected children develop severe bacterial and viral infections within the first 6 months of life and die before 1 year of age without treatment. Mutations in any of eight known genes: IL2RG, ARTEMIS, RAG1, RAG2, ADA, CD45, JAK3, and IL7R cause SCID. Mutations in unidentified genes may also cause SCID. Population-based genotype and allelic frequencies of these gene defects have not been measured. Some minimal estimates of SCID prevalence are presented. Currently, hematopoietic stem cell transplants are the standard treatment. In clinical trials, gene therapy has been used to reconstitute immune function in patients with IL2RG and ADA defects. The availability of effective therapies, plus the short asymptomatic period after birth, (when stem-cell transplantation is most effective), make SCID a potentially good candidate for newborn screening. Dried blood spots are currently collected from all infants at birth for newborn metabolic screening. Tests for TCLP on dried blood spots could be developed as a screen for SCID. Because SCID may be unrecognized, with infant deaths from infection attributed to other causes, newborn screening is the only way to ascertain true birth prevalence. Validated tests and pilot population studies are necessary to determine newborn screening's potential for identifying infants with SCID.

The conservative physiology of the immune system

Current immunological opinion disdains the necessity to define global interconnections between lymphocytes and regards natural autoantibodies and autoreactive T cells as intrinsically pathogenic. Immunological theories address the recognition of foreignness by independent clones of lymphocytes, not the relations among lymphocytes or between lymphocytes and the organism. However, although extremely variable in cellular/molecular composition, the immune system preserves as invariant a set of essential relations among its components and constantly enacts contacts with the organism of which it is a component. These invariant relations are reflected, for example, in the life-long stability of profiles of reactivity of immunoglobulins formed by normal organisms (natural antibodies). Oral contacts with dietary proteins and the intestinal microbiota also result in steady states that lack the progressive quality of secondary-type reactivity. Autoreactivity (natural autoantibody and autoreactive T cell formation) is also stable and lacks the progressive quality of clonal expansion. Specific immune responses, currently regarded as the fundament of the operation of the immune system, may actually result from transient interruptions in this stable connectivity among lymphocytes. More permanent deficits in interconnectivity result in oligoclonal expansions of T lymphocytes, as seen in Omenn's syndrome and in the experimental transplantation of a suboptimal diversity of syngeneic T cells to immunodeficient hosts, which also have pathogenic consequences. Contrary to theories that forbid autoreactivity as potentially pathogenic, the physiology of the immune system is conservative and autoreactive. Pathology derives from failures of these conservative mechanisms.

Recombinase activating gene enzymes of lymphocytes

Expression of T-cell receptor and surface immunoglobulins on T and B lymphocytes, respectively, is strictly dependent on the variable, (diversity) joining exon (V(D)J) recombination process, which is initiated by the lymphoid-specific recombinase activating gene proteins 1 and 2 (RAG1 and RAG2). Recent advances have highlighted the functional organization of the RAG1 and RAG2 proteins and have provided important information on the regulation of RAG gene expression. Depending on the severity of their effects on the V(D)J recombination process, mutations of the RAG genes account for a spectrum of combined immune deficiencies in humans.