Omenn syndrome (OS) is a rare variant of severe combined immunodeficiency characterized by susceptibility to severe opportunistic infections and peculiar manifestations, such as protein-losing erythroderma, alopecia, hepatosplenomegaly, lymphadenopathies, and severe diarrhea. The typical form of the disease is caused by hypomorphic mutation of the recombination-activating genes (RAG1 and RAG2), which are critical in initiating the molecular processes leading to lymphocyte and immunoglobulin receptor formation. Affected patients lack B cells, whereas autoreactive oligoclonal T cells infiltrate the skin, gut, spleen, and liver. In the absence of hematopoietic stem cell transplantation, patients with OS usually succumb early in life because of opportunistic infections. The incidence of OS is estimated to be <1 per 1 000 000; however, the actual frequency is difficult to ascertain. We report 2 siblings affected by OS due to a homozygous frameshift mutation (NM_000448.3:c.519delT, p.E174Sfs*26) in the RAG1 gene presenting with nonimmune hydrops fetalis (NIHF). To the best of our knowledge, this is the first reported association between OS and NIHF. NIHF specifically refers to the presence of ≥2 abnormal fluid collections in the fetus, without red blood cell alloimmunization. A broad spectrum of pathologies is associated with NIHF; however, in ∼20% of the cases, the primary cause remains unclear. Understanding the etiology of NIHF is essential for guiding clinical management, determining prognosis, and informing parents regarding recurrence risk. Our case contributes to expanding the spectrum of OS presentation and highlights the importance of a complete immunologic and genetic workup in otherwise unexplained cases of NIHF.
Recombination-activating gene (RAG) (RAG1 and RAG2) mutations are associated with a broad spectrum of clinical phenotypes, ranging from severe combined immunodeficiency (SCID) to various autoimmune diseases. RAG1 and RAG2 encode recombinase enzymes, which play a critical role in initiating the processes of lymphocyte receptor formation. Nonsense mutations in RAG1 and RAG2 fully annul T- and B-lymphocyte receptor formation, leading to T−B−NK+ SCID,1 whereas residual recombinase activity causes the expansion of oligoclonal T-lymphocyte populations. Omenn syndrome (OS) is a severe immunodeficiency often caused by hypomorphic mutations in the RAG family leading the generation of autoreactive oligoclonal T cells, which expand in the periphery and infiltrate, particularly, barrier tissues organs, such as the skin and gut.2 Patients present with generalized lichenified protein-losing erythroderma, subsequently progressing to exfoliation; furthermore, severe alopecia is a characteristic clinical indicator.1,2 The rash is usually present at birth or arises within the first days of life, evolving over the first few weeks.2,3 Hepatosplenomegaly and axillary and inguinal lymphadenopathy are usually encountered. Immunologic investigations reveal T lymphocytosis, with a highly activated phenotype, dominated by a restricted oligoclonal T-cell expansion.1 T lymphocytes’ proliferation response to phytohemagglutinin is reduced to <30% of the normal value, and indicators of thymopoiesis and B lymphocytes are absent, with natural killer cells generally present in normal numbers.1,3 Serum immunoglobulins M, A, and G are absent, but immunoglobulin E (IgE) levels are usually increased with associated eosinophilia.1,3 Initial management includes antimicrobial prophylaxis, immunoglobulin replacement, and topical immunosuppressive treatments. In the absence of hematopoietic stem cell transplantation, patients with OS usually succumb early in life to opportunistic infections.
Hydrops fetalis refers to pathologic fluid accumulation in fetal soft tissues and serous cavities and is defined by the presence of ≥2 abnormal fluid collections in the fetus on ultrasound images.4 These include ascites, pleural and/or pericardial effusions, and generalized skin edema (with skin thickness >5 mm).4 Other associated findings include placental edema and polyhydramnios.4 Nonimmune hydrops fetalis (NIHF) refers specifically to hydrops not caused by red blood cell alloimmunization4 and represents up to 90% of cases,4 with an estimated incidence of 1 in every 1700 to 3000 pregnancies.4 The precise pathogenesis of NIHF depends on the underlying disorder; however, the common pathophysiology is an imbalance in the regulation of fluid movement between the vascular and interstitial spaces, with a final fluid overload.5 A broad spectrum of pathologies are associated with NIHF, such as cardiovascular disorders, lymphatic dysplasia, fetal anemia, chromosomal abnormalities and syndromes, congenital infections, thoracic malformations, and inborn errors of metabolism5 ; however, in ∼20% of cases, the primary cause remains unknown.4
Here, we report the first case of 2 siblings affected by OS due to RAG1 mutation presenting with NIHF. Informed consent was obtained from the parents of all subjects involved in this case report.
Case Presentation
The proband was the third son of healthy nonconsanguineous Moroccan parents. The mother’s medical history was unremarkable until 32 weeks’ gestation, when a prenatal ultrasound revealed polyhydramnios with associated fetal biometry in the >95th percentile, without other signs. The proband was born at 32 + 6/7 weeks’ gestation by cesarean delivery because of the unrestrainable progression of maternal labor. At delivery, the infant was severely edematous (Fig 1 A–C), hypotonic, and bradycardic. He was intubated and subsequently admitted to the NICU. His birth weight was 2600 g (98th percentile), his length was 42 cm (28th percentile), and his head circumference was 34 cm (99th percentile). A chest radiograph revealed skin edema and pulmonary opacities, with right pleural effusion on the thoracic ultrasound. His hemoglobin level was low (10 g/dL); however, results of direct antigen testing, the Kleihauer-Betke test, and hemoglobin electrophoresis were normal. NIHF was suspected because of skin edema, right pleural effusion, and polyhydramnios. The result of an infectious disease workup (including rubella, enterovirus, cytomegalovirus, herpes simplex virus, syphilis, toxoplasmosis, and parvovirus B19) was negative. The infant required mechanical ventilation and inotropic support for 10 days and was subsequently weaned to noninvasive ventilation. An echocardiogram revealed a small patent ductus arteriosus. After the first week of life, he developed moderate intermittent neutropenia (1000 cells per mm3), cholestasis, mild hypoalbuminemia, severe alopecia, and an erythrodermic rash with progression to exfoliation (Fig 1D). Axillary and inguinal lymphadenopathies and hepatosplenomegaly became apparent at 2 weeks and were confirmed through MRI. On day 25, he developed right-ear chondritis (Fig 2) with fistulization; methicillin-resistant Staphylococcus aureus infection (from ear swab and blood) was treated with vancomycin. Karyotyping confirmed a normal 46 XY, whereas genomic microarray did not reveal any copy number variation but identified regions of homozygosity in 5 chromosomes, suggesting unknown common ancestry. The results of extended metabolic newborn screening (NBS), next-generation sequencing for RASopathies, and tests for lysosomal storage diseases were normal. An immunologic workup revealed the absence of serum immunoglobulins (immunoglobulin M, immunoglobulin A, and immunoglobulin G) and an increased IgE level, whereas extended immunophenotyping (Table 1) indicated T lymphocytosis, with a highly activated phenotype, dominated by a restricted oligoclonal T-cell pattern and absence of B lymphocytes. A diagnosis of T−B−NK+ SCID, with suspicion of OS, was made. Immunologic investigations excluded maternal engraftment. Wide-spectrum antibiotics with cotrimoxazole, acyclovir, and intravenous immunoglobulins were administered. Cyclosporin A and steroids ameliorated the erythroderma. A haploidentical hematopoietic stem cell transplant was performed at the age of 4 months. A next-generation sequencing panel for SCID confirmed the OS diagnosis, identifying a homozygous frameshift mutation in RAG1 (c.519delT, p.E174Sfs*26) located in one of the homozygosity regions that resulted in N-terminal truncated protein, with residual recombination activity already reported in association with SCID.6 Both parents were revealed to be carriers of the mutation (Fig 3). Four months after the hematopoietic stem cell transplant, a 100% stable lymphoid chimerism was observed. The patient was ultimately discharged from the hospital at 10 months with multidisciplinary follow-up.
A–C, Skin appearance at birth: edematous, tight, and translucent. D, Skin appearance after first week of life revealed an erythrodermic rash with severe exfoliation and alopecia.
A–C, Skin appearance at birth: edematous, tight, and translucent. D, Skin appearance after first week of life revealed an erythrodermic rash with severe exfoliation and alopecia.
Pedigree of family reveals homozygous RAG1 (c.519delT) in the 2 siblings and a heterozygous RAG1 (c.519delT) variant in both parents. The parents deny any consanguinity, but they come from the same Moroccan city.
Pedigree of family reveals homozygous RAG1 (c.519delT) in the 2 siblings and a heterozygous RAG1 (c.519delT) variant in both parents. The parents deny any consanguinity, but they come from the same Moroccan city.
Lymphocyte Subsets Analysis
| Lymphocyte Subset | Patient Values | Reference Valuesa |
|---|---|---|
| CD3+, cells per μL | 6206 | 2908–5961 |
| CD3+CD4+, % | 46.3 | 29.9–64.7 |
| HLA antigen DR+ | 34.3 | 0.8–6.1 |
| Naive | 0 | 68.8–91.7 |
| Effector memory | 95.4 | 1.5–8.3 |
| CD3+CD8+, % | 40.1 | 9.1–26.9 |
| HLA antigen DR+ | 29.9 | 1.6–30.2 |
| Naive | 0 | 37.9–90.7 |
| Effector memory | 92.2 | 1.3–27.2 |
| CD19, % | 0 | 11.2–33.2 |
| CD3−CD56+CD16+, cells per μL | 675 | 273–1698 |
| Lymphocyte Subset | Patient Values | Reference Valuesa |
|---|---|---|
| CD3+, cells per μL | 6206 | 2908–5961 |
| CD3+CD4+, % | 46.3 | 29.9–64.7 |
| HLA antigen DR+ | 34.3 | 0.8–6.1 |
| Naive | 0 | 68.8–91.7 |
| Effector memory | 95.4 | 1.5–8.3 |
| CD3+CD8+, % | 40.1 | 9.1–26.9 |
| HLA antigen DR+ | 29.9 | 1.6–30.2 |
| Naive | 0 | 37.9–90.7 |
| Effector memory | 92.2 | 1.3–27.2 |
| CD19, % | 0 | 11.2–33.2 |
| CD3−CD56+CD16+, cells per μL | 675 | 273–1698 |
Extended immunophenotype: T lymphocytes, despite being at the upper limits for age, are almost exclusively effector cells highly activated, whereas cells belonging to the most recent maturation stages are absent. B lymphocytes are also absent. The data are compatible with a form of SCID T−B−NK+.
Values are presented as 10th and 90th percentiles on the basis of established values for infants 0–12 mo.
The proband’s family history was remarkable for a sibling who died at 20 days of life of cardiorespiratory failure and bilateral massive bronchopneumonia. The infant was born at 36 weeks’ gestation after a preterm premature rupture of membranes. The mother’s medical history was unremarkable; nevertheless, a prenatal ultrasound just before delivery revealed severe polyhydramnios with pleuric bilateral effusion and mild ascites. The newborn was severely edematous at birth, and blood tests revealed leukocytosis with transient eosinophilia. Red blood cell alloimmunization was excluded, and a diagnosis of NIHF with unknown etiology was made. A histologic examination of the placenta revealed hyperplacentosis. The newborn immediately developed severe respiratory insufficiency with pulmonary hypertension and systemic hypotension with cardiac failure. Mechanical ventilation and inotropic support were provided. At 20 days old, the neonate died of cardiorespiratory failure. The result of an infection workup was negative. Postmortem investigations revealed massive abscess and necrotizing lymphogranulocyte infiltration in both lungs. The results of extended metabolic NBS and genetic testing for surfactant deficiency and α-thalassemia were normal. A DNA sample was subsequently tested for familial RAG1 mutation, and the same homozygous mutation found in his younger brother was confirmed.
Discussion
We report on 2 siblings, both manifesting NIHF, who were affected by OS due to a homozygous frameshift mutation (the NM_000448.3:c.519delT) in the RAG1 gene. RAG deficiency may manifest as a broad range of phenotypes that reflect the degree of adaptive immunity compromise. Null mutations are responsible for typical SCID, whereas OS is sustained by hypomorphic RAG variants, typically caused by frameshift mutations in the N-terminus of RAG1, as seen in our case.7 Data obtained from US NBS revealed that RAG deficiency accounted for 11% of all the cases of SCID and 41.2% of the cases of atypical SCID and OS.7 Nevertheless, no data in literature describe its association with NIHF; furthermore, previous prenatal diagnoses of RAG mutations are only reported in fetuses without ultrasonographic abnormalities with a positive family history of OS.8 In our cases, fetal hydrops arose in the late third trimester, with a more severe phenotype in the deceased sibling likely due to the delivery taking place in a more advanced gestational period and perpetuation of the etiopathogenetic mechanism, which remains unclear. We hypothesized that the cutaneous and gut involvement in OS (which is characterized by a severe inflammatory signature2 with a protein-losing erythroderma) led to a reduction in intravascular osmotic pressure and fluid extravasation, resulting in a final fluid overload. In literature, anecdotical cases of immunodeficiency are described in association with NIHF, such as IPEX (immune dysregulation, polyendocrinopathy, enteropathy, X-linked), hyper-IgE syndrome,9 or IKAROS haploinsufficiency.10 Except for the latter, which was described in a newborn with NIHF and congenital pancytopenia,10 all other cases were associated with remarkable ultrasound anomalies and resulted in pregnancy termination or fetal demise.9 Considering that mortality of NIHF remains high (55%–90%, depending on the cause),4 understanding its etiology is essential for guiding clinical management and informing parents regarding the prognosis. Because many rare diseases can cause NIHF, with 131 genes with strong evidence and 46 genes with emerging evidence for an association with NIHF,11 a genetic workup is essential. However, standard genetic testing with karyotyping or chromosomal microarray identifies the cause in 25% of cases and does not detect single-gene disorders.9 Interestingly, 2 recent studies9,12 revealed a diagnostic yield of prenatal exome sequencing of 29% and 50%, respectively, in cases of NIHF with a negative standard workup result. In our cases, RAG1 mutation clearly explains the phenotype presented by the first proband; nevertheless, the parents’ unreported common ancestry could claim an alternative autosomal recessive diagnostic hypothesis. This represents a limitation of the study; however, we analyzed all the 23 morbid genes contents in the homozygosity areas revealed at genomic microarray, and none was closely associated with our patients’ phenotypes. The strength in the management of our cases was the early diagnosis made in the younger brother, driven exclusively by the clinical phenotype despite the absence of similar data in literature or specific SCID NBS, which later provided the diagnosis also in the deceased sibling.
Conclusions
Our study contributes to expanding the spectrum of OS presentation, highlighting a possible association with NIHF and suggesting a novel and precocious OS clinical manifestation. These data support the importance of a complete immunologic and genetic workup in otherwise unexplained cases of NIHF.
Acknowledgments
We thank all the doctors in the Pediatric Oncohematology and Bone Marrow Transplant Unit, Children’s Hospital, Spedali Civili, Brescia, Italy. We thank the doctors Olga Calabrese and Stanghellini Ilaria (Medical Genetic Unit, Mother-Child Department, University Hospital of Modena), who performed the Array CGH (Comparative Genomic Hybridization) analysis. We thank the parents of the patients and all the doctors and nurses who cared for the patients.
Dr Valeri conceptualized and designed the study, drafted the initial manuscript, and reviewed and revised the manuscript; Dr Lugli, Prof Iughetti, and Dr Soresina critically analyzed and interpreted data and revised the article; Prof Giliani conducted initial analyses and reviewed and revised the manuscript; Prof Berardi and Dr Porta conceptualized and designed the study, coordinated and supervised data collection, and critically reviewed the manuscript; and all authors approved the final manuscript as submitted and agree to be accountable for all aspects of the work.
FUNDING: No external funding.
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