De novo mutations, genetic mosaicism and human disease

A transient mutational burst occurs during yeast colony development

Characterizing the contribution of mutators to mutation accumulation is essential for understanding cellular adaptation and diseases like cancer. By measuring single and double mutation rates, including point mutations, segmental duplications, and reciprocal translocations, we found that wild-type yeast colonies exhibit double mutation rates up to 17 times higher than expected from experimentally determined single mutation rates. These double mutants retained wild-type mutation rates, indicating they originated from genetically normal cells that transiently expressed a mutator phenotype. Numerical simulations suggest that transient mutator subpopulations likely consist of less than a few thousand cells, and experience high-intensity mutational bursts for less than five generations. Most double mutations accumulated sequentially across cell cycles, with simultaneous acquisition being rare and likely linked to systemic genomic instability. Additionally, we explored the genetic control of transient hypermutation and found that the excess of double mutants can be modulated by replication stress and the DNA damage tolerance pathway. Our findings suggest that transient mutators play a significant role in genomic instability and contribute to the mutational load accumulating in growing isogenic populations.

Male gamete copies to characterize genome inheritance and generate progenies

Male factor infertility accounts for approximately 30% of infertility cases. When spermatozoa are extremely scarce, replicating the male gamete to fertilize a large cohort of oocytes is ideal. Additionally, patients with inherited disorders currently rely on pre-implantation genetic testing (PGT) to select healthy embryos, which raises ethical concerns owing to the generation of multiple embryos to select one healthy conceptus. Therefore, it would be beneficial to decode the genetics of a single sperm cell before conceptus generation. In this study, we demonstrated the feasibility of replicating the sperm genome via androgenesis and selecting the desired gamete before fertilization to preserve a specific paternal genotype, as confirmed by phenotypic observations and genetic testing in a murine model. We achieved satisfactory pre-implantation development rates with replicated male gametes and generated healthy offspring. Specifically, using 8-cell stage androgenetic embryos, a single spermatozoon can yield up to three conceptuses carrying an identical paternal haplotype.

Increased caries risk in a Xerostomic patient with Darier disease: a case report of incipient and advanced carious lesions

Darier disease is a rare autosomal dominant inherited skin disorder, caused by mutations in the ATP2A2 gene. Oral manifestations can include mucosal lesions, salivary gland involvement, and xerostomia, that can significantly increase the risk of dental caries. A 58-year-old female with a confirmed diagnosis of Darier disease presented with oral manifestations, including recurrent sublingual blisters, xerostomia, and carious lesions. The intraoral examination revealed white spot carious lesions and cavitated caries, particularly in the cervical areas of several teeth. Dental treatment included fluoride mouthrinse, oral hygiene instructions, and restorative care for the cavitated teeth. The patient was also advised on preventive and symptomatic measures for xerostomia. Dentists should be aware of these potential issues and provide appropriate preventive, etiologic and symptomatic care. Regular follow-ups are essential to monitor the progression of dental lesions and manage oral health in patients with Dd.

The influence of cell source on the senescence of human mesenchymal stem/stromal cells

While mesenchymal stem/stromal cells (MSCs) exhibit the ability to self-renew, they are not immortal; they eventually reach a point of irreversible growth cessation and functional deterioration following a limited series of population doublings, referred to as replicative senescence. When evaluated according to the criteria set by the International Society for Cell Therapy (ISCT), MSCs show significant differences in their senescence patterns and other characteristics related to their phenotype and function. These differences are attributed to the source of the MSCs and the conditions in which they are grown. MSCs derived from fetal or adult sources have variations in their genome stability, as well as in the expression and epigenetic profile of the cells, which in turn affects their secretome. Understanding the key factors of MSC senescence based on cell source can help to develop effective strategies for regulating senescence and improving the therapeutic potential.

Clinical and Neuropsychological Phenotyping of Individuals With Somatic Variants in Neurodevelopmental Disorders

Background and Objectives

Somatic variants in brain-related genes can cause neurodevelopmental disorders, but detailed characterizations of their clinical phenotypes, neurobehavioral profiles, and comparisons with individuals with germline variants are limited.

Methods

Using data from the Simons Searchlight natural history cohort, which uses standardized parent-report data collection methods, we identified individuals with neurodevelopmental disorders caused by pathogenic somatic variants and examined their phenotypic data. We further used results from standardized measurements of adaptive functioning, social behavior, and emotional and behavioral problems to compare individuals with somatic variants with those with germline variants.

Results

We identified 15 probands with pathogenic or likely pathogenic somatic variants in the Simons Searchlight cohort. For 8 individuals with detailed phenotype information, symptoms included developmental delay or language delay (n = 8), hypotonia (n = 5), autism spectrum disorder (n = 4), and epilepsy (n = 3). Individuals with mosaic variants showed a range of severity in their scores on standardized measurements of adaptive functioning, social behavior, and emotional and behavioral problems. In particular, some individuals with mosaic variants showed impairments that were similar in severity or more severe compared with individuals with germline variants in the same gene.

Discussion

This study improves our understanding of the clinical phenotypes and neuropsychological profiles of individuals with mosaic pathogenic variants in neurodevelopmental disorders.

Potential Role of ABCF2 Gene in Pudendal Nerve Neuropathy and Interstitial Cystitis

BACKGROUND/OBJECTIVES

Symptoms of pudendal nerve neuropathy may overlap with various symptoms of interstitial cystitis (IC). As documented, there is a well-established correlation between the genes involved in ATP metabolism, neuropathy, and IC. ATP-binding cassette (ABC) transporters genes, in fact, are vital for ATP signaling. This study aims to associate the ABCF2 gene with a suspected pudendal nerve neuropathy and IC.

METHODS

Histological analysis was conducted for diagnosing IC while the genetic variant was identified by whole exome sequencing (WES) Trio and confirmed through Sanger.

RESULTS

We report a patient with IC, confirmed by histological examination, presenting with a suspected bladder and pudendal nerve neuropathy, though not analytically confirmed. Histological analysis revealed urothelial detachment caused by a dense subepithelial lymphocytic infiltrate, predominantly composed of mast cells, which serve as key diagnostic markers for interstitial cystitis (IC). WES analysis identified the heterozygous genetic variant c.1253T>G p.Phe418Cys within ABCF2 gene, precisely in its functional domain which actively operates in the hydrolysis of ATP energizing various biological systems. As reported, this gene displays high expression patterns in bladder tissue. The variant, absent in the healthy brother, was inherited from the father which presents mosaicism. The in silico prediction analyses classified this variant as pathogenic, identifying potential alterations in the protein structure.

CONCLUSIONS

Although the precise role of ABCF2 should be supported by further studies, we hypothesize that its disruption might impair ATP metabolism, likely altering the nociceptive response and leading to the patient's neuropathy. Further analyses are imperative to validate this research, for laying the groundwork for a specific therapy targeting the genetic dysregulation involved in this condition.

Micrognathia as a Diagnosis Marker for the Prenatal Identification of Edwards Syndrome

Background/Objectives: Edwards syndrome, or trisomy 18, is a severe chromosomal disorder marked by numerous congenital anomalies, including micrognathia. This study evaluated the diagnostic significance of micrognathia as a prenatal indicator for trisomy 18 through a case series involving five confirmed instances. Methods: Ultrasound assessments concentrated on the inferior facial angle (IFA) and the jaw index, supplemented by Non-Invasive Prenatal Testing (NIPT) and karyotyping. Results: Micrognathia was consistently identified alongside other anomalies, reinforcing its reliability as an ultrasound marker for trisomy 18. Conclusions: The findings highlight the critical nature of early detection for informed parental counseling and effective pregnancy management.

Incidental Diagnosis of Christmas Disease in a 5-year-old Child: A Case Report

Case description

A 5-year-old boy presented with bleeding gums following a fall from the swing. Initial treatment at a private clinic involved clot removal and gauze application. Despite no prior history of abnormal bleeding, the child experienced delayed and continuous bleeding, prompting further evaluation. Blood tests revealed normal prothrombin time (PT) but abnormal activated partial thromboplastin time (APTT), indicating a coagulation disorder. Vitamin K was administered, but profuse bleeding recurred, leading to hospital admission. Further tests confirmed a diagnosis of mild hemophilia B with low factor IX levels. The patient received fresh frozen plasma (FFP) transfusion, which stopped the bleeding. Follow-up showed a clean injury site after intervention.

Conclusion and clinical significance

This case underscores the need for high suspicion, thorough investigation, and prompt management in bleeding disorders, especially since patients may be unaware of their condition until a bleeding episode occurs.

How to cite this article

Gaviappa D, Shetty AK, Jeniffer N, et al. Incidental Diagnosis of Christmas Disease in a 5-year-old Child: A Case Report. Int J Clin Pediatr Dent 2025;18(2):235-238.

Genomic mosaicism in colorectal cancer and polyposis syndromes: a systematic review and meta-analysis

BACKGROUND

Colorectal cancer (CRC) and polypoid syndromes are significant public health concerns, with somatic mosaicism playing a crucial role in their genetic diversity. This study aimed to investigate the prevalence and impact of somatic mosaicism in these conditions.

METHODS

A search was conducted using PubMed, Scopus, and Web of Sciences to identify studies evaluating mosaicism in patients with CRC or polyposis syndromes. Odds ratios (ORs) with 95% confidence intervals (CIs) were calculated to determine prevalence rates. Statistical analyses were performed using R software 4.3.

RESULTS

A total of 27 studies, encompassing 2272 patients, were included in the analysis. Of these, 108 patients exhibited somatic mosaicism, resulting in an overall prevalence of 8.79% (95% CI 5.1 to 14.70%, I2 = 85; p < 0.01). Subgroup analyses revealed a significantly higher prevalence of mosaicism in patients with APC mutations (OR 13.43%, 95% CI 6.36 to 26.18%, I2 = 87; p < 0.01). Additionally, mosaicism in MLH1 and MSH2 genes was observed at rates of 2.75% (95% CI 1.20 to 6.18%) and 9.69% (95% CI 2.98 to 27.24%), respectively.

CONCLUSIONS

Our findings support the growing recognition of mosaicism as a critical factor in CRC susceptibility and underscore the importance of incorporating mosaicism screening into routine genetic testing for at-risk patients.

Case Report: Concurrent de novo pathogenic variants in the LMNA gene as a cause of sporadic partial lipodystrophy

Introduction

Inherited lipodystrophies are a group of rare diseases defined by severe reduction in adipose tissue mass and classified as generalized or partial. We report a non-familial (sporadic) case of partial lipodystrophy caused by a novel genetic mechanism involving closely linked de novo pathogenic variants in the LMNA gene.

Methods

A female adult with partial lipodystrophy and her parents were evaluated for gene variants across the exome under different mendelian inheritance models (autosomal dominant, recessive, compound heterozygous, and X-linked) to find pathogenic variants. Body composition was assessed via dual-energy X-ray absorptiometry (DXA).

Results

The patient showed absence of adipose tissue in the limbs; preservation of adiposity in the face, neck, and trunk; muscular hypertrophy, hypertriglyceridemia and insulin resistance. DXA revealed a fat mass of 15.4%, with android-to-gynoid ratio, trunk/limb, and trunk/leg ratios exceeding the published upper limits of 90% reference intervals. Two heterozygous missense de novo pathogenic variants in cis within the LMNA gene were found in the proband: p.Y481H and p.K486N (NP_733821.1). These variants have functional effects and were reported in inherited Emery-Dreifuss muscular dystrophy 2 (p.Y481H) and familial partial lipodystrophy type 2 (p.K486N). Molecular modeling analyses provided additional insights into the protein instability conferred by these variants in the lamin A/C Ig-like domain.

Conclusion

In a case of sporadic partial lipodystrophy, we describe two concurrent de novo pathogenic variants within the same gene (LMNA) as a novel pathogenic mechanism. This finding expands the genetic and phenotypic spectrum of partial lipodystrophy and laminopathy syndromes.

Novel postzygotic RASA1 mutation in a patient with Parkes Weber syndrome: A case report and literature review

Key Clinical Message

Not only germline but also postzygotic mutations in the RASA1 or EPHB4 genes can lead to capillary malformation-arteriovenous malformation (CM-AVM) syndrome. As it is not always possible to clinically distinguish between constitutional variants and postzygotic mosaicism, a sufficiently high sequencing depth must be used in genetic diagnostics to detect both.

Abstract

Capillary malformation-arteriovenous malformation (CM-AVM) syndrome, with or without Parkes Weber syndrome, is a rare autosomal dominant disease caused by pathogenic RASA1 or EPHB4 variants. Up to 80% of CM-AVM cases have an affected parent. Gene panel sequencing was performed for a 4-year-old girl with multiple CMs, two capillary stains on the left leg, and associated overgrowth of the second toe. We also reviewed published cases with mosaic RASA1 and EPHB4 mutations. A mosaic RASA1 loss-of-function mutation was detected with a variant allele frequency (VAF) of 20% in the blood and oral epithelial cells of the index patient. The literature review illustrates that the severity of the clinical phenotype does not correlate with the VAF. We also identified a germline nonsense variant in the patient's TEK gene. However, inactivating TEK variants do not cause a vascular phenotype but can confer an increased risk for primary congenital glaucoma with variable expressivity. The case presented here illustrates that the choice of the sequencing depth of a diagnostic next-generation sequencing test for CM-AVM patients should always take mosaicism into account and that a good knowledge of the sequenced genes and associated disease mechanisms is necessary for adequate genetic counseling.

Decoding complex inherited phenotypes in rare disorders: the DECIPHERD initiative for rare undiagnosed diseases in Chile

Rare diseases affect millions of people worldwide, and most have a genetic etiology. The incorporation of next-generation sequencing into clinical settings, particularly exome and genome sequencing, has resulted in an unprecedented improvement in diagnosis and discovery in the past decade. Nevertheless, these tools are unavailable in many countries, increasing health care gaps between high- and low-and-middle-income countries and prolonging the "diagnostic odyssey" for patients. To advance genomic diagnoses in a setting of limited genomic resources, we developed DECIPHERD, an undiagnosed diseases program in Chile. DECIPHERD was implemented in two phases: training and local development. The training phase relied on international collaboration with Baylor College of Medicine, and the local development was structured as a hybrid model, where clinical and bioinformatics analysis were performed in-house and sequencing outsourced abroad, due to lack of high-throughput equipment in Chile. We describe the implementation process and findings of the first 103 patients. They had heterogeneous phenotypes, including congenital anomalies, intellectual disabilities and/or immune system dysfunction. Patients underwent clinical exome or research exome sequencing, as solo cases or with parents using a trio design. We identified pathogenic, likely pathogenic or variants of unknown significance in genes related to the patients´ phenotypes in 47 (45.6%) of them. Half were de novo informative variants, and half of the identified variants have not been previously reported in public databases. DECIPHERD ended the diagnostic odyssey for many participants. This hybrid strategy may be useful for settings of similarly limited genomic resources and lead to discoveries in understudied populations.

Hypoxia, NSAIDs, and autism: A biocultural analysis of stressors in gametogenesis

Cultural and generational trends have increasingly favored "anti-inflammatory" action, innovating a new class of analgesic, non-steroidal anti-inflammatory drugs (NSAIDs) in the 20th century. The modern human body has been molded over evolutionary time and while acknowledging inflammation can be pathologically entwined, it also serves an important role in healthy folliculogenesis and ovulation, shaping cues that drive needed vascular change. This review argues that because of anti-inflammatory action, the cultural invention of NSAIDs represents a particular stressor on female reproductive-age bodies, interacting with natural, underlying variation and placing limits on healthy growth and development in the follicles, creating potential autism risk through hypoxia and mutagenic or epigenetic effects. Since testes are analogs to ovaries, the biological grounding extends naturally to spermatogenesis. This review suggests the introduction of over-the-counter NSAIDs in the 1980s failed to recognize the unique functioning of reproductive-age bodies, challenging the cyclical inflammation needed for healthy gamete development. NSAIDs are framed as one (notable) stressor in an anti-inflammatory era focused on taming the risks of inflammation in modern human life.

Case Report of Suspected Gonadal Mosaicism in FOXP1-Related Neurodevelopmental Disorder

Heterozygous mutations in the FOXP1 gene (OMIM#605515) are responsible for a well-characterized neurodevelopmental syndrome known as "intellectual developmental disorder with language impairment with or without autistic features" (OMIM#613670) or FOXP1 syndrome for short. The main features of the condition are global developmental delay/intellectual disability; speech impairment in all individuals, regardless of their level of cognitive abilities; behavioral abnormalities; congenital anomalies, including subtle dysmorphic features; and strabismus, brain, cardiac, and urogenital abnormalities. Here, we present two siblings with a de novo heterozygous FOXP1 variant, namely, a four-year-old boy and 14-month-old girl. Both children have significantly delayed early psychomotor development, hypotonia, and very similar, slightly dysmorphic facial features. A lack of expressive speech was the leading symptom in the case of the four-year-old boy. We performed whole-exome sequencing on the male patient, which identified a pathogenic heterozygous c.1541G>A (p.Arg514His) FOXP1 mutation. His sister's targeted mutation analysis also showed the same heterozygous FOXP1 variant. Segregation analysis revealed the de novo origin of the mutation, suggesting the presence of parental gonadal mosaicism. To the best of our knowledge, this is the first report of gonadal mosaicism in FOXP1-related neurodevelopmental disorders in the medical literature.

Genetic testing for non-parkinsonian movement disorders: Navigating the diagnostic maze

Genetic testing has become a valuable diagnostic tool for movement disorders due to substantial advancements in understanding their genetic basis. However, the heterogeneity of movement disorders poses a significant challenge, with many genes implicated in different subtypes. This paper aims to provide a neurologist's perspective on approaching patients with hereditary hyperkinetic disorders with a focus on select forms of dystonia, paroxysmal dyskinesia, chorea, and ataxia. Age at onset, initial symptoms, and their severity, as well as the presence of any concurrent neurological and non-neurological features, contribute to the individual clinical profiles of hereditary non-parkinsonian movement disorders, aiding in the selection of appropriate genetic testing strategies. There are also more specific diagnostic clues that may facilitate the decision-making process and may be highly specific for certain conditions, such as diurnal fluctuations and l-dopa response in dopa-responsive dystonia, and triggering factors, duration and frequency of attacks in paroxysmal dyskinesia. While the genetic and mutational spectrum across non-parkinsonian movement disorders is broad, certain groups of diseases tend to be associated with specific types of pathogenic variants, such as repeat expansions in many of the ataxias. Some of these pathogenic variants cannot be detected by standard methods, such as panel or exome sequencing, but require the investigation of intronic regions for repeat expansions, such as Friedreich's or FGF14-linked ataxia. With our advancing knowledge of the genetic underpinnings of movement disorders, the incorporation of precise and personalized diagnostic strategies can enhance patient care, prognosis, and the application and development of targeted therapeutic interventions.

Novel characterization of CASK variant c.1963 A>G (p.Asn655Asp) through whole-exome sequencing in a monochorionic diamniotic twin fetus with significant brain anomalies: A case report

Whole-exome sequencing is an evolving technology in perinatal diagnosis which allows identification of genetic etiologies that would otherwise go undetermined. In this case report, a 38-year-old Hispanic woman, G5P3013, with a monochorionic diamniotic twin gestation with one fetus displaying significant cranial abnormalities on prenatal ultrasound and magnetic resonance imaging (MRI) of the brain is presented. Fetal anomalies included bilateral ventriculomegaly, absent cavum septum pellucidum, and absent corpus callosum. Diagnostic amniocentesis with chromosome analysis, chromosomal microarray, alpha-fetoprotein, cytomegalovirus, toxoplasmosis, and parvovirus had normal results. Whole-exome sequencing for the anomalous fetus detected a de novo mosaic variant of uncertain significance (VUS) in the calcium/calmodulin dependent serine protein kinase (CASK) gene: c.1963 A > G (p.Asn655Asp). This variant was absent in the normal twin fetus, the mother, and the father. Pathogenic CASK gene mutations are associated with three syndromes: FG syndrome 4, intellectual developmental disorder and microcephaly with pontine and cerebellar hypoplasia (MICPCH), and intellectual developmental disorder with or without nystagmus. Whole-exome sequencing identified a potential etiology for the anomalies detected. The variant likely arose de novo and was the potential cause of the identified cranial abnormalities in one fetus of this monochorionic diamniotic twin gestation. Whole-exome sequencing may provide additional diagnostic utility when standard diagnostic testing is noncontributory.

Meta-analysis of 46,000 germline de novo mutations linked to human inherited disease

BACKGROUND

De novo mutations (DNMs) are variants that occur anew in the offspring of noncarrier parents. They are not inherited from either parent but rather result from endogenous mutational processes involving errors of DNA repair/replication. These spontaneous errors play a significant role in the causation of genetic disorders, and their importance in the context of molecular diagnostic medicine has become steadily more apparent as more DNMs have been reported in the literature. In this study, we examined 46,489 disease-associated DNMs annotated by the Human Gene Mutation Database (HGMD) to ascertain their distribution across gene and disease categories.

RESULTS

Most disease-associated DNMs reported to date are found to be associated with developmental and psychiatric disorders, a reflection of the focus of sequencing efforts over the last decade. Of the 13,277 human genes in which DNMs have so far been found, the top-10 genes with the highest proportions of DNM relative to gene size were H3-3 A, DDX3X, CSNK2B, PURA, ZC4H2, STXBP1, SCN1A, SATB2, H3-3B and TUBA1A. The distribution of CADD and REVEL scores for both disease-associated DNMs and those mutations not reported to be de novo revealed a trend towards higher deleteriousness for DNMs, consistent with the likely lower selection pressure impacting them. This contrasts with the non-DNMs, which are presumed to have been subject to continuous negative selection over multiple generations.

CONCLUSION

This meta-analysis provides important information on the occurrence and distribution of disease-associated DNMs in association with heritable disease and should make a significant contribution to our understanding of this major type of mutation.

In Utero Origins of Acute Leukemia in Children

Acute leukemias, mainly consisting of acute lymphoblastic leukemia (ALL) and acute myeloid leukemia (AML), comprise a major diagnostic group among hematologic cancers. Due to the early age at onset of ALL, particularly, it has long been suspected that acute leukemias of childhood may have an in utero origin. This supposition has motivated many investigations seeking direct proof of prenatal leukemogenesis, in particular, twin and "backtracking studies". The suspected in utero origin has also focused on gestation as a critical window of risk, resulting in a rich literature on prenatal risk factors for pediatric acute leukemias. In this narrative review, we recount the circumstantial and direct evidence for an in utero origin of childhood acute leukemias.

Choosing the Best Tissue and Technique to Detect Mosaicism in Fibrous Dysplasia/McCune-Albright Syndrome (FD/MAS)

GNAS-activating somatic mutations give rise to Fibrous Dysplasia/McCune-Albright syndrome (FD/MAS). The low specificity of extra-skeletal signs of MAS and the mosaic status of the mutations generate some difficulties for a proper diagnosis. We studied the clinical and molecular statuses of 40 patients referred with a clinical suspicion of FD/MAS to provide some clues. GNAS was sequenced using both Sanger and Next-Generation Sequencing (NGS). We were able to identify the pathogenic variants in 25% of the patients. Most of them were identified in the affected tissue, but not in blood. Additionally, NGS demonstrated the ability to detect more patients with mosaicism (8/34) than Sanger sequencing (4/39). Even if in some cases, the clinical information was not complete, we confirmed that, as in previous works, when the patients were young children with a single manifestation, such as hyperpigmented skin macules or precocious puberty, the molecular diagnosis was usually negative. In conclusion, as FD/MAS is caused by mosaic variants, it is essential to use sensitive techniques that allow for the detection of low percentages and to choose the right tissue to study. When not possible, and due to the low positive genetic rate, patients with FD/MAS should only be genetically tested when the clinical diagnosis is really uncertain.

Rare mosaic variant of GJA1 in a patient with a neurodevelopmental disorder

GJA1 is the causative gene for oculodentodigital dysplasia (ODDD). A novel de novo GJA1 variant, NM 000165:c263C > T [p.P88L], was identified in a mosaic state in a patient with short stature, seizures, delayed myelination, mild hearing loss, and tooth enamel hypoplasia. Although the patient exhibited severe neurodevelopmental delay, other clinical features of ODDD, including limb anomalies, were mild. This may be due to differences in the mosaic ratios in different organs.

Genomic variation in neurons

Neurons born during the fetal period have extreme longevity and survive until the death of the individual because the human brain has highly limited tissue regeneration. The brain is comprised of an enormous variety of neurons each exhibiting different morphological and physiological characteristics and recent studies have further reported variations in their genome including chromosomal abnormalities, copy number variations, and single nucleotide mutations. During the early stages of brain development, the increasing number of neurons generated at high speeds has been proposed to lead to chromosomal instability. Additionally, mutations in the neuronal genome can occur in the mature brain. This observed genomic mosaicism in the brain can be produced by multiple endogenous and environmental factors and careful analyses of these observed variations in the neuronal genome remain central for our understanding of the genetic basis of neurological disorders.

Rediscovering tandem repeat variation in schizophrenia: challenges and opportunities

Tandem repeats (TRs) are prevalent throughout the genome, constituting at least 3% of the genome, and often highly polymorphic. The high mutation rate of TRs, which can be orders of magnitude higher than single-nucleotide polymorphisms and indels, indicates that they are likely to make significant contributions to phenotypic variation, yet their contribution to schizophrenia has been largely ignored by recent genome-wide association studies (GWAS). Tandem repeat expansions are already known causative factors for over 50 disorders, while common tandem repeat variation is increasingly being identified as significantly associated with complex disease and gene regulation. The current review summarizes key background concepts of tandem repeat variation as pertains to disease risk, elucidating their potential for schizophrenia association. An overview of next-generation sequencing-based methods that may be applied for TR genome-wide identification is provided, and some key methodological challenges in TR analyses are delineated.

Sperm DNA damage: The possible link between obesity and male infertility, an update of the current literature

Obesity prevalence worldwide is increasing significantly. Whilst maternal obesity has clear detrimental impacts on fertility, pregnancy and foetal outcomes, more recently there has been an increasing focus on the role of paternal obesity in human fertility. Recent meta-analyses have indicated that obesity in men negatively affects basic sperm parameters such as sperm count, concentration and motility, increases the incidence of infertility and reduces the chances of conception. Sperm DNA damage, typically characterised by DNA strand breaks and oxidation of DNA nucleotides, is a specialised marker of sperm quality that has been independently associated with recurrent miscarriage, reduced assisted reproduction success and increased mutational loads in subsequent offspring. Whilst, there are still conflicting data in humans as to the association of obesity in men with sperm DNA damage, evidence from rodent models is clear, indicating that male obesity increases sperm DNA damage. Human data are often conflicting because of the large heterogeneity amongst studies, the use of body mass index as the indicator of obesity and the methods used for detection of sperm DNA damage. Furthermore, comorbidities of obesity (i.e., heat stress, adipokines, insulin resistance, changes in lipids, hypogonadism and obstructive sleep apnoea) are also independently associated with increased sperm DNA damage that is not always modified in men with obesity, and as such may provide a causative link to the discrepancies amongst human studies. In this review, we provide an update on the literature regarding the associations between obesity in men and fertility, basic sperm parameters and sperm DNA damage. We further discuss potential reasons for the discrepancies in the literature and outline possible direct and indirect mechanisms of increased sperm DNA damage resulting from obesity. Finally, we summarise intergenerational obesity through the paternal linage and how sperm DNA damage may contribute to the transmission.

Case Report: Characterization of known (c.607G>C) and novel (c.416C>G) ELANE mutations in two Mexican families with congenital neutropenia

The most common causes of congenital neutropenia are mutations in the ELANE (Elastase, Neutrophil Expressed) gene (19p13.3), mostly in exon 5 and the distal portion of exon 4, which result in different clinical phenotypes of neutropenia. Here, we report two pathogenic mutations in ELANE, namely, c.607G>C (p.Gly203Arg) and a novel variant c.416C>G (p.Pro139Arg), found in two Mexican families ascertained via patients with congenital neutropenia who responded positively to the granulocyte colony-stimulating factor (G-CSF) treatment. These findings highlight the usefulness of identifying variants in patients with inborn errors of immunity for early clinical management and the need to rule out mosaicism in noncarrier parents with more than one case in the family.

Clinical and mutational spectrum of paediatric Charcot-Marie-Tooth disease in a large cohort of Chinese patients

Background: Charcot-Marie-Tooth disease (CMT) is the most common inherited neurological disorder suffered in childhood. To date, the disease features have not been extensively characterized in the Chinese paediatric population. In this study, we aimed to analyse the clinical profiles and genetic distributions of a paediatric CMT cohort in China. Methods: A total of 181 paediatric CMT patients were enrolled. After preexcluding PMP22 duplication/deletion by multiplex ligation-dependent probe amplification (MLPA), Sanger sequencing, targeted next-generation sequencing (NGS) or whole-exome sequencing (WES) was performed to obtain a genetic diagnosis. Detailed information was collected to explore the spectrum of subtypes and genotype-phenotype correlations. Results: Pathogenic mutations were identified in 68% of patients in this study; with PMP22 duplication, MFN2 and GJB1 were the most frequent disease-causing genes. Of note, respect to the higher prevalence worldwide, CMT1A (18.2%) was relatively lower in our cohort. Besides, the mean age at onset (8.3 ± 5.7 years) was significantly older in our series. In genotype-phenotype analyse, PMP22 point mutations were considered the most severe genotypes and were mostly de novo. In addition, the de novo mutations were identified in up to 12.7% of all patients, which was higher than that in other studies. Conclusion: We identified a relatively lower detection rate of PMP22 duplication and a higher frequency of de novo variants among paediatric patients in China. We also identified the genetic and phenotypic heterogeneity of this cohort, which may provide clues for clinicians in directing genetic testing strategies for Chinese patients with early-onset CMT.

Somatic mosaicism in inborn errors of immunity: Current knowledge, challenges, and future perspectives

Inborn errors of immunity (IEI) are a diverse group of monogenic disorders of the immune system due to germline variants in genes important for the immune response. Over the past decade there has been increasing recognition that acquired somatic variants present in a subset of cells can also lead to immune disorders or 'phenocopies' of IEI. Discovery of somatic mosaicism causing IEI has largely arisen from investigation of seemingly sporadic cases of IEI with predominant symptoms of autoinflammation and/or autoimmunity in which germline disease-causing variants are not detected. Disease-causing somatic mosaicism has been identified in genes that also cause germline IEI, such as FAS, and in genes without significant corresponding germline disease, such as UBA1 and TLR8. There are challenges in detecting low-level somatic variants, and it is likely that the extent of the somatic mosaicism causing IEI is largely uncharted. Here we review the field of somatic mosaicism leading to IEI and discuss challenges and methods for somatic variant detection, including diagnostic approaches for molecular diagnoses of patients.

Chromatin remodeler Activity-Dependent Neuroprotective Protein (ADNP) contributes to syndromic autism

BACKGROUND

Individuals affected with autism often suffer additional co-morbidities such as intellectual disability. The genes contributing to autism cluster on a relatively limited number of cellular pathways, including chromatin remodeling. However, limited information is available on how mutations in single genes can result in such pleiotropic clinical features in affected individuals. In this review, we summarize available information on one of the most frequently mutated genes in syndromic autism the Activity-Dependent Neuroprotective Protein (ADNP).

RESULTS

Heterozygous and predicted loss-of-function ADNP mutations in individuals inevitably result in the clinical presentation with the Helsmoortel-Van der Aa syndrome, a frequent form of syndromic autism. ADNP, a zinc finger DNA-binding protein has a role in chromatin remodeling: The protein is associated with the pericentromeric protein HP1, the SWI/SNF core complex protein BRG1, and other members of this chromatin remodeling complex and, in murine stem cells, with the chromodomain helicase CHD4 in a ChAHP complex. ADNP has recently been shown to possess R-loop processing activity. In addition, many additional functions, for instance, in association with cytoskeletal proteins have been linked to ADNP.

CONCLUSIONS

We here present an integrated evaluation of all current aspects of gene function and evaluate how abnormalities in chromatin remodeling might relate to the pleiotropic clinical presentation in individual"s" with Helsmoortel-Van der Aa syndrome.

Novel de novo ZNF148 truncating variant causing autism spectrum disorder, attention deficit hyperactivity disorder, and intellectual disability

ZNF148 gene is a Krüppel-type transcription factor that has transcriptional regulatory function. Heterozygous variant in ZNF148 gene causes an intellectual disability syndrome characterized by global developmental delay, absence, or hypoplasia of corpus callosum, wide intracerebral ventricles, and dysmorphic facial features, while its associations with ASD and ADHD have not been reported. We report a new patient with intellectual disability, autism spectrum disorder (ASD) and attention-deficit hyperactivity disorder (ADHD). The patient had a novel heterozygous truncating variant c.1818dupC (p.Lys607Glnfs*11) in the ZNF148 gene. This variation produces a ZNF148 truncated protein with a deletion of the C-terminal activation domain and may destabilize the protein by affecting the transcriptional activation function. Brain MRI shows normal brain development. Here, we identify a novel ZNF148 heterozygous truncating variant in a patient with distinct phenotypes of ASD and ADHD, which expands the genotype-phenotype spectrum of ZNF148, and indicates ZNF148 is also a potential target gene for ASD.