[Two cases of cytopenia associated with multiple malformations]

The first patient, a 10-year-old girl, presented with pancytopenia and recurrent epistaxis, along with a history of repeated upper respiratory infections, café-au-lait spots, and microcephaly. Genetic testing revealed compound heterozygous mutations in the DNA ligase IV (LIG4) gene, leading to a diagnosis of LIG4 syndrome. The second patient, a 6-year-old girl, was seen for persistent thrombocytopenia lasting over two years and was noted to have short stature, hyperpigmented skin, and hand malformations. She had a positive result from chromosome breakage test. She was diagnosed with Fanconi anemia complementation group A. Despite similar clinical presentations, the two children were diagnosed with different disorders, suggesting that children with hemocytopenia and malformations should not only be evaluated for hematological diseases but also be screened for other potential underlying conditions such as immune system disorders.

Novel Compound Heterozygous Mutations of LIG4 Gene in an Indian LIG4 Syndrome Patient with Severe Microcephaly: Case Report, In-silico Analysis and Systematic Review

BACKGROUND

LIG4 syndrome, characterized by immunodeficiency, sensitivity to ionizing radiations, intrauterine growth retardation, postnatal growth retardation, and microcephaly, is a rare genetic disorder caused by pathogenic variants of the LIG4 gene. Few patients are presented with no immune dysregulation as well.

CASE STUDY

We present here a male child of 2 years and 4 months of age with severe microcephaly and short stature. His birth weight was 1.9 Kg, and his current height, weight, and head circumference are 83.2 cm (z score = -2.37), 9.5 Kg (z score = -2.76), and 36 cm (z score = -9.24), respectively. Possible causative pathogenic compound heterozygous variants of the LIG4 gene, which were inherited from the parents, were identified by whole exome sequencing of the DNA of the patient and his parents. A systematic review of the literature is also performed to summarize the patients of LIG4 syndrome reported worldwide and summarize the associated genetic mutations of the LIG4 gene. Compound heterozygous variants (c.597_600delTCAG/ c.342del) of LIG4 gene were identified. The parents were found to be heterozygous carriers of one variant each.

CONCLUSION

The in-silico analysis of identified variants explains their effect on the structure and function of the LIG4 protein hence explaining the genotype-phenotype correlation.

[LIG4 syndrome: a report of four cases and literature review]

Objective: To analyze clinical, immunological and genetic characteristics of 4 cases of LIG4 syndrome. Methods: We retrospectively analyzed the clinical data of 4 patients from 3 families with LIG4 syndrome who were admitted to Children's Hospital of the Capital Institute of Pediatrics from June 2017 to May 2018, and reviewed related articles, the clinical, immunological and genetic characteristics of LIG4 syndrome were summarized and analyzed. Results: Those 4 cases (P1 to P4), including 2 males and 2 females, had an average age of 1.5 years. All of them presented with special facial features, such as microcephaly, beak-like-nose, and receding forehead. Three of them presented with delayed physical development. P3 suffered from mental retardation and P4 had feeding difficulty. BCG scars were repeatedly ruptured in 3 cases, 4 cases had pneumonia, 1 case had EB virus infection, 2 cases had cytomegalovirus infection, 1 case had fungal infection, and 1 case had chronic diarrhea. Blood routine tests showed decreased neutrophil and lymphocyte counts. Immunoassay showed decreased absolute count of CD4(+)T lymphocyte and B lymphocyte, with normal CD8(+)T cells. P1, P2 presented with decreased immunoglobulin. All of those patients had LIG4 gene complex heterozygous mutations, of whom one had missense mutation had mild clinical phenotype and another three cases had frameshift mutation presented with severe clinical phenotype. One patient underwent hematopoietic stem cell transplantation, and has established normal immune function. He did not have recurrent infection during one year follow-up period. The other 3 patients had preventive anti-infection treatment and received regular human immunoglobulin infusion, but they still had recurrent infection. In literature review, 67 articles were retrieved, totally 37 case were reported, showing special faces and recurrent infection as characteristic presentation of this disease. Conclusions: The typical manifestations of LIG4 syndrome are microcephaly, special facial features and repeated infection. The average age at diagnosis of LIG4 syndrome was more than one year old. If a patient presented with microcephaly, BCG scar infection and leukopenia, LIG4 syndrome should be considered. Immunoglobulin is decreased at different degrees, and CD4(+) and CD19(+) lymphocyte counts always decrease, Naive T and B cells decrease more prominently, and CD8(+)T cells were normal in patients with typical LIG4 syndrome. It is effective to reconstruction of immune system with bone marrow transplantation in LIG4 syndrome patients.

A Novel Missense LIG4 Mutation in a Patient With a Phenotype Mimicking Behçet's Disease

DNA ligase IV (LIG4) syndrome is a rare autosomal recessive disorder, manifesting with variable immune deficiency, growth failure, predisposition to malignancy, and cellular sensitivity to ionizing radiation. The facial features are subtle and variable, as well. Herein, we described an 18-year-old boy, the first child of consanguineous parents who presented with Behçet's disease (BD)-like phenotype, developmental delay, and dysembryoplastic neuroepithelial tumor (DNET). Whole-exome sequencing revealed a homozygous p.Arg871His (c.2612G > A) mutation in LIG4. To date, 35 cases have been reported with LIG4 syndrome. Peripheral blood mononuclear cells of the patient displayed notable sensitivity to ionizing radiation. Flow cytometric annexin V-propidium iodide (PI) and eFluor670 proliferation assays showed accelerated radiation-induced apoptosis and diminished proliferation, respectively. To our knowledge, this is the first case presenting with a BD-like phenotype. This case provides further evidence that rare monogenic defects could be the underlying cause of atypical presentations of some well-described disorders. Moreover, this clinical report further expands the phenotypical spectrum of LIG4 deficiency.

Novel compound heterozygous DNA ligase IV mutations in an adolescent with a slowly-progressing radiosensitive-severe combined immunodeficiency

We herein describe a case of a 17-year-old boy with intractable common warts, short stature, microcephaly and slowly-progressing pancytopenia. Simultaneous quantification of T-cell receptor recombination excision circles (TREC) and immunoglobulin κ-deleting recombination excision circles (KREC) suggested very poor generation of both T-cells and B-cells. By whole exome sequencing, novel compound heterozygous mutations were identified in the patient's DNA ligase IV (LIG4) gene. The diagnosis of LIG4 syndrome was confirmed by delayed DNA double-strand break repair kinetics in γ-irradiated fibroblasts from the patient and their restoration by an introduction of wild-type LIG4. Although the patient received allogeneic hematopoietic stem cell transplantation from his haploidentical mother, he unfortunately expired due to an insufficiently reconstructed immune system. An earlier definitive diagnosis using TREC/KREC quantification and whole exome sequencing would thereby allow earlier intervention, which would be essential for improving long-term survival in similar cases with slowly-progressing LIG4 syndrome masked in adolescents.

The spatial organization of non-homologous end joining: from bridging to end joining

Non-homologous end joining (NHEJ) repairs DNA double-strand breaks generated by DNA damage and also those occurring in V(D)J recombination in immunoglobulin and T cell receptor production in the immune system. In NHEJ DNA-PKcs assembles with Ku heterodimer on the DNA ends at double-strand breaks, in order to bring the broken ends together and to assemble other proteins, including DNA ligase IV (LigIV), required for DNA repair. Here we focus on structural aspects of the interactions of LigIV with XRCC4, XLF, Artemis and DNA involved in the bridging and end-joining steps of NHEJ. We begin with a discussion of the role of XLF, which interacts with Ku and forms a hetero-filament with XRCC4; this likely forms a scaffold bridging the DNA ends. We then review the well-defined interaction of XRCC4 with LigIV, and discuss the possibility of this complex interrupting the filament formation, so positioning the ligase at the correct positions close to the broken ends. We also describe the interactions of LigIV with Artemis, the nuclease that prepares the ends for ligation and also interacts with DNA-PK. Lastly we review the likely affects of Mendelian mutations on these multiprotein assemblies and their impacts on the form of inherited disease.