DNA double-strand breaks (DSBs) are the most severe type of DNA damage in living organisms and are primarily repaired by two pathways: non-homologous end joining (NHEJ) and homologous recombination (HR). DNA ligase IV (LIG4) is essential for the final step of NHEJ, where it facilitates the rejoining of DSBs. Loss-of-function mutations in the LIG4 gene result in LIG4 syndrome, a condition characterized by combined immunodeficiency, developmental delay, microcephaly and radiosensitivity. In this study, we investigated cellular senescence, radiosensitivity, and X-ray radiation-induced chromosome aberrations induced in newly developed Lig4 mutant (Lig4W447C/W447C) mouse cells. The results showed that Lig4W447C/W447C cells exhibited accelerated cellular senescence, possibly due to increased accumulation of spontaneous DSBs. Radiosensitivity assays revealed that Lig4W447C/W447C cells were four times more radiosensitive than wild-type cells. Moreover, analysis of both X-ray radiation-induced chromatid-type and chromosome-type aberrations revealed that both break-type aberrations (e.g., fragments) and exchange-type aberrations (e.g., dicentrics) were increased in Lig4W447C/W447C cells compared to wild-type cells. These results suggest that in addition to causing inefficient DNA break, end-joining, the novel mutation in Lig4 may promote misrejoining of X-ray radiation-induced DSBs.

DNA ligase IV (LIG4) deficiency is a rare autosomal recessive disorder associated with impaired DNA damage-response mechanisms. LIG4 deficiency exhibits a broad clinical spectrum, including microcephaly, facial abnormalities, sensitivity to ionizing radiation, ranging from severe combined immunodeficiency to normal immune function, progressive bone marrow failure, and predisposition to malignancy. We report an 18-year-old girl of consanguineous Turkish parents, first evaluated at 13 years old for growth retardation and short stature. She was born preterm at 32 weeks with dysmorphic facial features, lissencephaly, intellectual disability, and without immunodeficiency. Although diagnosed with growth hormone deficiency, she did not receive appropriate hormone therapy due to special circumstances. At the age of 15, she presented with primary amenorrhea. Further evaluation revealed hypergonadotropic hypogonadism due to gonadal failure. Genetic analysis revealed a homozygous c.2440C>T (p.Arg814Ter) mutation in the LIG4 gene. Following genetic counseling, her parents opted for prenatal diagnosis in a subsequent pregnancy, resulting in the birth of another child with the same condition. LIG4 syndrome should be considered in the differential diagnosis of cases with growth retardation, microcephaly, and gonadal failure. In the literature, there are limited cases reported with gonadal failure in LIG4 syndrome. Here, we emphasize this aspect to highlight its significance.

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. 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. 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.

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. 患儿1，女，10岁，因全血细胞减少伴反复鼻衄就诊，有反复上呼吸道感染史，有皮肤咖啡斑、小头畸形，基因检测发现DNA连接酶IV（ligase IV, LIG4）基因存在复合杂合变异，诊断为LIG4综合征。患儿2，女，6岁，因血小板减少2年余就诊，有身材矮小、皮肤黝黑、手部畸形等，染色体断裂试验检查结果为阳性，诊断为范可尼贫血互补组A型。该2例患儿临床表现相似，最终诊断为两类疾病，提示血细胞减少伴畸形的患儿并非仅是血液病，需警惕免疫系统等其他疾病。.

Severe ventriculomegaly is a rare congenital brain defect, usually detected in utero, of poor neurodevelopmental prognosis. This ventricular enlargement can be the consequence of different mechanisms: either by a disruption of the cerebrospinal fluid circulation or abnormalities of its production/absorption. The aqueduct stenosis is one of the most frequent causes of obstructive ventriculomegaly, however, fewer than 10 genes have been linked to this condition and molecular bases remain often unknown. We report here 4 fetuses from 2 unrelated families presenting with ventriculomegaly at prenatal ultra-sonography as well as an aqueduct stenosis and skeletal abnormalities as revealed by fetal autopsy. Genome sequencing identified biallelic pathogenic variations in LIG4, a DNA-repair gene responsible for the LIG4 syndrome which associates a wide range of clinical manifestations including developmental delay, microcephaly, short stature, radiation hypersensitivity and immunodeficiency. Thus, not only this report expands the phenotype spectrum of LIG4-related disorders, adding ventriculomegaly due to aqueduct stenosis, but we also provide the first neuropathological description of fetuses carrying LIG4 pathogenic biallelic variations.