Objective: To explore the clinical and genetic characteristics of dyskeratosis congenita (DC). Methods: A retrospective analysis was conducted on the clinical, laboratory, imaging, pathological, genetic, and treatment data of 6 DC patients diagnosed at the Children's Hospital of Zhejiang University School of Medicine from January 2010 to June 2025. Results: Among the 6 DC patients, 1 case was of Hoyeraal-Hreidarsson syndrome, 4 were male, and 2 were female. The diagnosis age 0.9-6.1 years. All 6 cases presented with bone marrow failure; 5 cases had a classic triad of skin and mucous membrane (mucosal leukoplakia, abnormal skin pigmentation, nail dystrophy); 5 cases had growth retardation, among which 2 cases had intrauterine growth retardation. Two cases had diarrhea and 1 case had abnormal liver function; 1 case had stiff and deformed limbs, accompanied by limited mobility, and dry and obstructive balanitis; 1 case had recurrent eyelid inflammation, middle ear inflammation, and nasal inflammation. All 6 cases had decreased B cell numbers, and 4 cases also had decreased natural killer cell numbers. There were 3 cases of children with cytomegalovirus (CMV) infection, of which 1 case of CMV infection led to retinal frosted branch angiitis and subsequent intracranial CMV infection resulting in death, and 1 case had CMV enteritis and died of hemophagocytic syndrome. Among 4 cases of boys, 3 cases had DKC1 gene variations and 1 case had an unknown variation gene; 2 cases of girls had TINF2 gene variations. The TINF2 c.860T>A (p.L287Q) variation site was a new mutation. Among 6 patients with DC, 2 cases died, 3 cases survived and 1 case was lost to follow-up. Conclusions: The DKC1 and TINF2 genes are common pathogenic genes in patients with DC. Bone marrow failure is a clue for the early identification of DC. The triad of skin and mucous membrane is its typical clinical manifestation. Children with DC generally have reduced B cells and natural killer killer cells, and have a high risk of fatal CMV infection. The overall prognosis is poor. 目的： 探讨先天性角化不良（DC）的临床及基因特征。 方法： 病例系列研究，回顾性收集2010年1月至2025年6月在浙江大学医学院附属儿童医院确诊的6例DC患儿的临床、实验室、影像、病理、基因、治疗资料。 结果： 6例DC患儿中，男4例、女2例，确诊年龄0.9~6.1岁，其中Hoyeraal-Hreidarsson综合征1例。6例患儿均出现骨髓衰竭，有典型皮肤黏膜三联征（黏膜白斑、皮肤色素异常、甲营养不良）5例，生长发育迟缓5例，其中2例存在宫内发育迟缓。腹泻2例，肝功能异常1例，1例患儿四肢关节僵硬、畸形，伴活动受限，同时有干燥闭塞性龟头炎，1例患儿反复眼睑炎、中耳炎、鼻炎。6例患儿均存在B细胞减少，4例同时合并自然杀伤细胞减少。3例患儿发生巨细胞病毒（CMV）感染，其中1例CMV感染导致视网膜霜枝样血管炎，后续颅内CMV感染后死亡；1例患儿存在CMV肠炎，合并噬血细胞综合而死亡。4例男童中3例为DKC1基因变异，1例变异基因不详，2例女童为TINF2基因变异，其中TINF2 c.860T>A（p.L287Q）变异位点为新发变异。存活3例，死亡2例，失访1例。 结论： DKC1、TINF2基因是DC患儿常见的致病基因，骨髓衰竭是DC早期识别的线索，皮肤黏膜三联征是其典型临床表现，DC患儿普遍存在B细胞、自然杀伤细胞减少，致命性CMV感染风险高，DC总体预后较差。.

Telomeres protect the ends of chromosomes but shorten following cell division in the absence of telomerase activity. When telomeres become critically short or damaged, a DNA damage response is activated. Telomeres then become dysfunctional and trigger cellular senescence or death. Telomere shortening occurs with ageing and may contribute to associated maladies such as infertility, neurodegeneration, cancer, lung dysfunction and haematopoiesis disorders. Telomere dysfunction (sometimes without shortening) is associated with various diseases, known as telomere biology disorders (also known as telomeropathies). Telomere biology disorders include dyskeratosis congenita, Høyeraal-Hreidarsson syndrome, Coats plus syndrome and Revesz syndrome. Although mouse models have been invaluable in advancing telomere research, full recapitulation of human telomere-related diseases in mice has been challenging, owing to key differences between the species. In this Review, we discuss telomere protection, maintenance and damage. We highlight the differences between human and mouse telomere biology that may contribute to discrepancies between human diseases and mouse models. Finally, we discuss recent efforts to generate new 'humanized' mouse models to better model human telomere biology. A better understanding of the limitations of mouse telomere models will pave the road for more human-like models and further our understanding of telomere biology disorders, which will contribute towards the development of new therapies.

To explore the clinical features and genetic etiology of a child with Hoyeraal-Hreidarsson syndrome (HHS). A child with HHS diagnosed at the Affiliated Hospital of Jining Medical University due to "developmental delay and anaemia" on April 27, 2024 was selected as the study subject. Clinical data of the child was collected. Genomic DNA was extracted from peripheral blood samples of the child and his family members. Whole-exome sequencing was carried out, and candidate variant was verified by Sanger sequencing of his family members and bioinformatics analysis using CASAVA v1.8.2. The pathogenicity of the candidate variant was rated according to the Standards and Guidelines for the Interpretation of Sequence Variants released by the American College of Medical Genetics and Genomics (ACMG). Relevant literature on HHS cases reported in China was reviewed to analyze the clinical and genetic characteristics. This study was approved by the Medical Ethics Committee of the Hospital (Ethics No.: 2024-10-C003). The child, a 7-month-old boy, had mainly manifested with growth retardation, developmental delay, microcephaly, cerebellar hypoplasia, immunodeficiency and bone marrow failure. Routine blood test indicated pancytopenia. The immunological workup showed reduction of B cells, NK cells and immunoglobulins. Cranial MRI demonstrated the volume of bilateral cerebellar hemispheres and brainstem and corpus callosum was small. Whole-exome sequencing revealed that he has harbored a hemizygous c.103_105del (p.Glu35del) variant of the DKC1 gene. Sanger sequencing showed that his mother and two sisters have carried the same variant. Based on the ACMG guidelines, the variant was predicted to be likely pathogenic (PM1+PM4+PS4_Supporting+PM2_Supporting). Four relevant literature were retrieved, which has involved 8 HHS cases. Together with the patient from this study, they have consisted of 8 males and 1 females. The most common symptoms of the 9 patients were blood system abnormalities and developmental delay. All patients had shown cerebellar dysplasia and anemia/erythrocytopenia. Among them, 3 cases have harbored TINF2 gene variants, and 6 cases had harbored DKC1 gene variants. The c.103_105del variant has not been reported in China previously. The hemizygous c.103_105del (p.Glu35del) variant of the DKC1 gene probably underlay the disease in this child. Above finding has expanded the mutational and phenotypic spectra of the DKC1 gene, and has facilitated early diagnosis of HHS in this child.

RTEL1 is an essential DNA helicase that plays multiple roles in genome stability and telomere length regulation. The ultra-long telomeres of the house mouse hinder its utility as a model for telomere-related diseases. We have previously generated a mouse model with human-length telomeres, termed "Telomouse," by substituting methionine 492 of mouse Rtel1 to a lysine (Rtel1M492K). In humans, a methionine to isoleucine mutation at this position causes the fatal telomere biology disorder Hoyeraal-Hreidarsson syndrome (HHS). Here, we introduced the Rtel1M492I point mutation into the mouse genome, generating another mouse model, which we termed "HHS mouse." The HHS mouse telomeres are not as short as those of the Telomouse but nevertheless display higher levels of telomeric DNA damage, fragility, and recombination, associated with anaphase bridges and micronuclei. The HHS mouse also exhibits aberrant hematopoiesis and pre-fibrotic alterations in the lung. These observations indicate that the two mutations at the same codon separate critical functions of RTEL1: Rtel1M492K mainly reduces the telomere length setpoint, while Rtel1M492I predominantly disrupts telomere protection. The two mouse models enable dissecting the mechanistic roles of RTEL1 and the different contributions of short telomeres and DNA damage to telomere biology disorders and genomic instability.

People with intellectual disability suffer complex challenges due to adaptive functioning limitations, high rates of chronic diseases and shortened lifespans compared with the general population. Telomere shortening is a hallmark of ageing, and short telomeres are linked to neurological disorders. The main objective of this systematic review and meta-analysis was to identify any differences in telomere length and the rate of telomere attrition in leukocytes and fibroblasts from people with intellectual disability and controls. PubMed, Scopus and ScienceDirect were searched. Articles that compared telomere length in individuals with intellectual disability to apparently healthy age-matched controls were included. Risk of bias was assessed using the AXIS tool and data were analysed using CMA. Fifteen studies comprised of 17 comparisons provided data and were included in meta-analyses. Compared with healthy controls (N = 481), people with intellectual disability (N = 366) from a known genetic syndrome (Cri du chat, Down, Hoyeraal-Hreidarsson, Williams or Nicolaides-Baraitser) possessed shorter leukocyte telomeres (SMD: -0.853 [95% CI: -1.622 to -0.084], p = 0.03). Similarly, relative to controls (N = 16), people with syndromic intellectual disability (N = 21) possessed shorter fibroblast telomeres (-1.389 [-2.179 to -0.599], p = 0.001). Furthermore, people with syndromic forms of intellectual disability also demonstrated a faster rate (2.09-fold) of telomere shortening. Consistent with epidemiological findings on mortality and morbidity risk, people with syndromic intellectual disability appear to undergo a faster rate of biological ageing compared to the general population. These findings emphasise the need for healthy ageing lifestyle (i.e., exercise and stress management) and therapeutic interventions for people with syndromic intellectual disability.