Genome sequencing differentiates a paracentric inversion from a balanced insertion enabling more accurate preimplantation genetic testing.

INTRODUCTION: Distinguishing paracentric inversions (PAIs) from chromosomal insertions has traditionally relied on fluorescent in situ hybridization (FISH) techniques, but recent advancements in high-throughput sequencing have enabled the use of genome sequencing for such differentiation. In this study, we present a 38-year-old male carrier of a paracentric inversion on chromosome 2q, inv (2)(q31.2q34), whose partner experienced recurrent miscarriages. MATERIAL AND METHODS: FISH analysis confirmed the inversion, and genome sequencing was employed for detailed characterization. RESULTS: Preimplantation genetic testing (PGT) revealed that all assessed embryos were balanced, consistent with the low risk of unbalanced offspring associated with PAIs. While PAI carriers traditionally exhibit low risk of producing unbalanced offspring, exceptions exist due to crossover events within the inversion loop. Although the sample size was limited, the findings align with existing sperm study data, supporting the rare occurrence of unbalanced progeny in PAI carriers. CONCLUSIONS: This study highlights the possibility of characterizing PAIs using genome sequencing to enable correct reproductive counseling and PGT decisions. Detailed characterization of a PAI is crucial for understanding potential outcomes and guiding PGT strategies, as accurate knowledge of the inversion size is essential for appropriate method selection in PGT. Given the very low risk of unbalanced offspring in PAI carriers, routine PGT may not be warranted but should be considered in specific cases with a history of unbalanced progeny or recurrent miscarriages. This study contributes to our understanding of PAI segregation and its implications for reproductive outcomes.

The Risk of Cholesteatoma in Individuals With First-degree Relatives Surgically Treated for the Disease.

Importance: Cholesteatoma in the middle ear is not regarded as a hereditary disease, but case reports of familial clustering exist in the literature, as well as observed familial cases in the clinical work. However, the knowledge regarding cholesteatoma as a hereditary disease is lacking in the literature. Objective: To assess the risk of cholesteatoma in individuals with a first-degree relative surgically treated for the same disease. Design, Setting, and Participants: In this nested case-control study in the Swedish population between 1987 and 2018 of first-time cholesteatoma surgery identified from the Swedish National Patient Register, 2 controls per case were randomly selected from the population register through incidence density sampling, and all first-degree relatives for cases and controls were identified. Data were received in April 2022, and analyses were conducted between April and September 2022. Exposure: Cholesteatoma surgery in a first-degree relative. Main Outcomes and Measures: The main outcome was first-time cholesteatoma surgery. The association between having a first-degree relative with cholesteatoma and the risk of cholesteatoma surgery in the index persons was estimated by odds ratios (ORs) and 95% CIs through conditional logistic regression analysis. Results: Between 1987 and 2018, 10 618 individuals with a first-time cholesteatoma surgery (mean [SD] age at surgery, 35.6 [21.5] years; 6302 [59.4%] men) were identified in the Swedish National Patient Register. The risk of having a cholesteatoma surgery was almost 4 times higher in individuals having a first-degree relative surgically treated for the disease (OR, 3.9; 95% CI, 3.1-4.8), but few cases were exposed overall. Among the 10 105 cases with at least 1 control included in the main analysis, 227 (2.2%) had at least 1 first-degree relative treated for cholesteatoma, while the corresponding numbers for controls were 118 of 19 553 control patients (0.6%). The association was stronger for individuals under the age of 20 years at first surgery (OR, 5.2; 95% CI, 3.6-7.6) and for a surgery involving the atticus and/or mastoid region (OR, 4.8; 95% CI, 3.4-6.2). There was no difference in the prevalence of having a partner with cholesteatoma between cases and controls (10 cases [0.3%] and 16 controls [0.3%]; OR, 0.92; 95% CI, 0.41-2.05), which implies that increased awareness does not explain the association. Conclusions and Relevance: In this Swedish case-control study using nationwide register data with high coverage and completeness, the findings suggest that the risk of cholesteatoma in the middle ear is strongly associated with a family history of the condition. Family history was nevertheless quite rare and can therefore only explain a limited number of all cases; these families could be an important source for information regarding the genetic background for cholesteatoma disease.

A Missense Variant in PDK1 Associated with Severe Neurodevelopmental Delay and Epilepsy.

The pyruvate dehydrogenase complex (PDC) is responsible for the conversion of pyruvate into acetyl-CoA, which is used for energy conversion in cells. PDC activity is regulated by phosphorylation via kinases and phosphatases (PDK/PDP). Variants in all subunits of the PDC and in PDK3 have been reported, with varying phenotypes including lactic acidosis, neurodevelopmental delay, peripheral neuropathy, or seizures. Here, we report a de novo heterozygous missense variant in PDK1 (c.1139G > A; p.G380D) in a girl with developmental delay and early onset severe epilepsy. To investigate the role of PDK1G380D in energy metabolism and neuronal development, we used a zebrafish model. In zebrafish embryos we show a reduced number of cells with mitochondria with membrane potential, reduced movements, and a delay in neuronal development. Furthermore, we observe a reduction in the phosphorylation of PDH-E1α by PDKG380D, which suggests a disruption in the regulation of PDC activity. Finally, in patient fibroblasts, a mild reduction in the ratio of phosphorylated PDH over total PDH-E1α was detected. In summary, our findings support the notion that this aberrant PDK1 activity is the cause of clinical symptoms in the patient.

Genome sequencing is a sensitive first-line test to diagnose individuals with intellectual disability.

PURPOSE: Individuals with intellectual disability (ID) and/or neurodevelopment disorders (NDDs) are currently investigated with several different approaches in clinical genetic diagnostics. METHODS: We compared the results from 3 diagnostic pipelines in patients with ID/NDD: genome sequencing (GS) first (N = 100), GS as a secondary test (N = 129), or chromosomal microarray (CMA) with or without FMR1 analysis (N = 421). RESULTS: The diagnostic yield was 35% (GS-first), 26% (GS as a secondary test), and 11% (CMA/FMR1). Notably, the age of diagnosis was delayed by 1 year when GS was performed as a secondary test and the cost per diagnosed individual was 36% lower with GS first than with CMA/FMR1. Furthermore, 91% of those with a negative result after CMA/FMR1 analysis (338 individuals) have not yet been referred for additional genetic testing and remain undiagnosed. CONCLUSION: Our findings strongly suggest that genome analysis outperforms other testing strategies and should replace traditional CMA and FMR1 analysis as a first-line genetic test in individuals with ID/NDD. GS is a sensitive, time- and cost-effective method that results in a confirmed molecular diagnosis in 35% of all referred patients.

Anophthalmia and microphthalmia in children: associated ocular, somatic and genetic morbidities and quality of life.

PURPOSE: To report ocular outcome, somatic co-morbidities, genetics, and quality of life in children born with anophthalmia (A) or microphthalmia (M). METHODS: Thirty-five children (19 boys) with A/M underwent ophthalmological examinations and a review of medical records. Parents of 12/22 cases completed the Pediatric Quality of Life Inventory (PedsQL). RESULTS: Age at examination ranged from 7 months to 18 years (median 2.3 years). Ten cases were totally blind or had light perception. Isolated A/M occurred in 16/35 cases, while somatic, psychomotor, neuroradiological and/or genetic pathology occurred in 19/35 cases both in the bilateral (7/9) and in the unilateral group (12/26). Among 26 unilateral cases, 4/16 with one normal eye had associated problems compared to 9/10 if the contralateral eye was pathological (p < .01). There was an increased risk for heart defects in children with psychomotor delay (p = .04). Pathogenic genetic abnormalities were identified in 10/24 cases. Neuroimaging demonstrated pathology in 14/20 cases with corpus callosum dysgenesis (6/20) being the most common. The median total PedsQL score of parent reports for ages 2-12 was 52.4 (range 22.6-100). CONCLUSIONS: Somatic, psychomotor and/or neuroradiological pathologies were more common in bila-teral than unilateral cases, but the difference was not significant. There was decreased risk in unilateral cases with one normal eye. Genetic defects occurred in both unilateral and bilateral cases. Health-related quality of life was reduced.

Integration of whole genome sequencing into a healthcare setting: high diagnostic rates across multiple clinical entities in 3219 rare disease patients.

BACKGROUND: We report the findings from 4437 individuals (3219 patients and 1218 relatives) who have been analyzed by whole genome sequencing (WGS) at the Genomic Medicine Center Karolinska-Rare Diseases (GMCK-RD) since mid-2015. GMCK-RD represents a long-term collaborative initiative between Karolinska University Hospital and Science for Life Laboratory to establish advanced, genomics-based diagnostics in the Stockholm healthcare setting. METHODS: Our analysis covers detection and interpretation of SNVs, INDELs, uniparental disomy, CNVs, balanced structural variants, and short tandem repeat expansions. Visualization of results for clinical interpretation is carried out in Scout-a custom-developed decision support system. Results from both singleton (84%) and trio/family (16%) analyses are reported. Variant interpretation is done by 15 expert teams at the hospital involving staff from three clinics. For patients with complex phenotypes, data is shared between the teams. RESULTS: Overall, 40% of the patients received a molecular diagnosis ranging from 19 to 54% for specific disease groups. There was heterogeneity regarding causative genes (n = 754) with some of the most common ones being COL2A1 (n = 12; skeletal dysplasia), SCN1A (n = 8; epilepsy), and TNFRSF13B (n = 4; inborn errors of immunity). Some causative variants were recurrent, including previously known founder mutations, some novel mutations, and recurrent de novo mutations. Overall, GMCK-RD has resulted in a large number of patients receiving specific molecular diagnoses. Furthermore, negative cases have been included in research studies that have resulted in the discovery of 17 published, novel disease-causing genes. To facilitate the discovery of new disease genes, GMCK-RD has joined international data sharing initiatives, including ClinVar, UDNI, Beacon, and MatchMaker Exchange. CONCLUSIONS: Clinical WGS at GMCK-RD has provided molecular diagnoses to over 1200 individuals with a broad range of rare diseases. Consolidation and spread of this clinical-academic partnership will enable large-scale national collaboration.

Cytogenetically visible inversions are formed by multiple molecular mechanisms.

Cytogenetically detected inversions are generally assumed to be copy number and phenotypically neutral events. While nonallelic homologous recombination is thought to play a major role, recent data suggest the involvement of other molecular mechanisms in inversion formation. Using a combination of short-read whole-genome sequencing (WGS), 10X Genomics Chromium WGS, droplet digital polymerase chain reaction and array comparative genomic hybridization we investigated the genomic structure of 18 large unique cytogenetically detected chromosomal inversions and achieved nucleotide resolution of at least one chromosomal inversion junction for 13/18 (72%). Surprisingly, we observed that seemingly copy number neutral inversions can be accompanied by a copy-number gain of up to 350 kb and local genomic complexities (3/18, 17%). In the resolved inversions, the mutational signatures are consistent with nonhomologous end-joining (8/13, 62%) or microhomology-mediated break-induced replication (5/13, 38%). Our study indicates that short-read 30x coverage WGS can detect a substantial fraction of chromosomal inversions. Moreover, replication-based mechanisms are responsible for approximately 38% of those events leading to a significant proportion of inversions that are actually accompanied by additional copy-number variation potentially contributing to the overall phenotypic presentation of those patients.

Presynaptic dysfunction in CASK-related neurodevelopmental disorders.

CASK-related disorders are genetically defined neurodevelopmental syndromes. There is limited information about the effects of CASK mutations in human neurons. Therefore, we sought to delineate CASK-mutation consequences and neuronal effects using induced pluripotent stem cell-derived neurons from two mutation carriers. One male case with autism spectrum disorder carried a novel splice-site mutation and a female case with intellectual disability carried an intragenic tandem duplication. We show reduction of CASK protein in maturing neurons from the mutation carriers, which leads to significant downregulation of genes involved in presynaptic development and of CASK protein interactors. Furthermore, CASK-deficient neurons showed decreased inhibitory presynapse size as indicated by VGAT staining, which may alter the excitatory-inhibitory (E/I) balance in developing neural circuitries. Using in vivo magnetic resonance spectroscopy quantification of GABA in the male mutation carrier, we further highlight the possibility to validate in vitro cellular data in the brain. Our data show that future pharmacological and clinical studies on targeting presynapses and E/I imbalance could lead to specific treatments for CASK-related disorders.

From cytogenetics to cytogenomics: whole-genome sequencing as a first-line test comprehensively captures the diverse spectrum of disease-causing genetic variation underlying intellectual disability.

BACKGROUND: Since different types of genetic variants, from single nucleotide variants (SNVs) to large chromosomal rearrangements, underlie intellectual disability, we evaluated the use of whole-genome sequencing (WGS) rather than chromosomal microarray analysis (CMA) as a first-line genetic diagnostic test. METHODS: We analyzed three cohorts with short-read WGS: (i) a retrospective cohort with validated copy number variants (CNVs) (cohort 1, n = 68), (ii) individuals referred for monogenic multi-gene panels (cohort 2, n = 156), and (iii) 100 prospective, consecutive cases referred to our center for CMA (cohort 3). Bioinformatic tools developed include FindSV, SVDB, Rhocall, Rhoviz, and vcf2cytosure. RESULTS: First, we validated our structural variant (SV)-calling pipeline on cohort 1, consisting of three trisomies and 79 deletions and duplications with a median size of 850 kb (min 500 bp, max 155 Mb). All variants were detected. Second, we utilized the same pipeline in cohort 2 and analyzed with monogenic WGS panels, increasing the diagnostic yield to 8%. Next, cohort 3 was analyzed by both CMA and WGS. The WGS data was processed for large (> 10 kb) SVs genome-wide and for exonic SVs and SNVs in a panel of 887 genes linked to intellectual disability as well as genes matched to patient-specific Human Phenotype Ontology (HPO) phenotypes. This yielded a total of 25 pathogenic variants (SNVs or SVs), of which 12 were detected by CMA as well. We also applied short tandem repeat (STR) expansion detection and discovered one pathologic expansion in ATXN7. Finally, a case of Prader-Willi syndrome with uniparental disomy (UPD) was validated in the WGS data. Important positional information was obtained in all cohorts. Remarkably, 7% of the analyzed cases harbored complex structural variants, as exemplified by a ring chromosome and two duplications found to be an insertional translocation and part of a cryptic unbalanced translocation, respectively. CONCLUSION: The overall diagnostic rate of 27% was more than doubled compared to clinical microarray (12%). Using WGS, we detected a wide range of SVs with high accuracy. Since the WGS data also allowed for analysis of SNVs, UPD, and STRs, it represents a powerful comprehensive genetic test in a clinical diagnostic laboratory setting.

Comprehensive structural variation genome map of individuals carrying complex chromosomal rearrangements.

Complex chromosomal rearrangements (CCRs) are rearrangements involving more than two chromosomes or more than two breakpoints. Whole genome sequencing (WGS) allows for outstanding high resolution characterization on the nucleotide level in unique sequences of such rearrangements, but problems remain for mapping breakpoints in repetitive regions of the genome, which are known to be prone to rearrangements. Hence, multiple complementary WGS experiments are sometimes needed to solve the structures of CCRs. We have studied three individuals with CCRs: Case 1 and Case 2 presented with de novo karyotypically balanced, complex interchromosomal rearrangements (46,XX,t(2;8;15)(q35;q24.1;q22) and 46,XY,t(1;10;5)(q32;p12;q31)), and Case 3 presented with a de novo, extremely complex intrachromosomal rearrangement on chromosome 1. Molecular cytogenetic investigation revealed cryptic deletions in the breakpoints of chromosome 2 and 8 in Case 1, and on chromosome 10 in Case 2, explaining their clinical symptoms. In Case 3, 26 breakpoints were identified using WGS, disrupting five known disease genes. All rearrangements were subsequently analyzed using optical maps, linked-read WGS, and short-read WGS. In conclusion, we present a case series of three unique de novo CCRs where we by combining the results from the different technologies fully solved the structure of each rearrangement. The power in combining short-read WGS with long-molecule sequencing or optical mapping in these unique de novo CCRs in a clinical setting is demonstrated.

Replicative and non-replicative mechanisms in the formation of clustered CNVs are indicated by whole genome characterization.

Clustered copy number variants (CNVs) as detected by chromosomal microarray analysis (CMA) are often reported as germline chromothripsis. However, such cases might need further investigations by massive parallel whole genome sequencing (WGS) in order to accurately define the underlying complex rearrangement, predict the occurrence mechanisms and identify additional complexities. Here, we utilized WGS to delineate the rearrangement structure of 21 clustered CNV carriers first investigated by CMA and identified a total of 83 breakpoint junctions (BPJs). The rearrangements were further sub-classified depending on the patterns observed: I) Cases with only deletions (n = 8) often had additional structural rearrangements, such as insertions and inversions typical to chromothripsis; II) cases with only duplications (n = 7) or III) combinations of deletions and duplications (n = 6) demonstrated mostly interspersed duplications and BPJs enriched with microhomology. In two cases the rearrangement mutational signatures indicated both a breakage-fusion-bridge cycle process and haltered formation of a ring chromosome. Finally, we observed two cases with Alu- and LINE-mediated rearrangements as well as two unrelated individuals with seemingly identical clustered CNVs on 2p25.3, possibly a rare European founder rearrangement. In conclusion, through detailed characterization of the derivative chromosomes we show that multiple mechanisms are likely involved in the formation of clustered CNVs and add further evidence for chromoanagenesis mechanisms in both "simple" and highly complex chromosomal rearrangements. Finally, WGS characterization adds positional information, important for a correct clinical interpretation and deciphering mechanisms involved in the formation of these rearrangements.

Whole-Genome Sequencing of Cytogenetically Balanced Chromosome Translocations Identifies Potentially Pathological Gene Disruptions and Highlights the Importance of Microhomology in the Mechanism of Formation.

Most balanced translocations are thought to result mechanistically from nonhomologous end joining or, in rare cases of recurrent events, by nonallelic homologous recombination. Here, we use low-coverage mate pair whole-genome sequencing to fine map rearrangement breakpoint junctions in both phenotypically normal and affected translocation carriers. In total, 46 junctions from 22 carriers of balanced translocations were characterized. Genes were disrupted in 48% of the breakpoints; recessive genes in four normal carriers and known dominant intellectual disability genes in three affected carriers. Finally, seven candidate disease genes were disrupted in five carriers with neurocognitive disabilities (SVOPL, SUSD1, TOX, NCALD, SLC4A10) and one XX-male carrier with Tourette syndrome (LYPD6, GPC5). Breakpoint junction analyses revealed microhomology and small templated insertions in a substantive fraction of the analyzed translocations (17.4%; n = 4); an observation that was substantiated by reanalysis of 37 previously published translocation junctions. Microhomology associated with templated insertions is a characteristic seen in the breakpoint junctions of rearrangements mediated by error-prone replication-based repair mechanisms. Our data implicate that a mechanism involving template switching might contribute to the formation of at least 15% of the interchromosomal translocation events.

Phenotype and genotype in 52 patients with Rubinstein-Taybi syndrome caused by EP300 mutations.

Rubinstein-Taybi syndrome (RSTS) is a developmental disorder characterized by a typical face and distal limbs abnormalities, intellectual disability, and a vast number of other features. Two genes are known to cause RSTS, CREBBP in 60% and EP300 in 8-10% of clinically diagnosed cases. Both paralogs act in chromatin remodeling and encode for transcriptional co-activators interacting with >400 proteins. Up to now 26 individuals with an EP300 mutation have been published. Here, we describe the phenotype and genotype of 42 unpublished RSTS patients carrying EP300 mutations and intragenic deletions and offer an update on another 10 patients. We compare the data to 308 individuals with CREBBP mutations. We demonstrate that EP300 mutations cause a phenotype that typically resembles the classical RSTS phenotype due to CREBBP mutations to a great extent, although most facial signs are less marked with the exception of a low-hanging columella. The limb anomalies are more similar to those in CREBBP mutated individuals except for angulation of thumbs and halluces which is very uncommon in EP300 mutated individuals. The intellectual disability is variable but typically less marked whereas the microcephaly is more common. All types of mutations occur but truncating mutations and small rearrangements are most common (86%). Missense mutations in the HAT domain are associated with a classical RSTS phenotype but otherwise no genotype-phenotype correlation is detected. Pre-eclampsia occurs in 12/52 mothers of EP300 mutated individuals versus in 2/59 mothers of CREBBP mutated individuals, making pregnancy with an EP300 mutated fetus the strongest known predictor for pre-eclampsia. © 2016 Wiley Periodicals, Inc.

Erratum.

[This corrects the article DOI: 10.1002/mgg3.177.].

Positive Attitudes towards Non-Invasive Prenatal Testing (NIPT) in a Swedish Cohort of 1,003 Pregnant Women.

OBJECTIVE: The clinical utilization of non-invasive prenatal testing (NIPT) for identification of fetal aneuploidies is expanding worldwide. The aim of this study was to gain an increased understanding of pregnant women's awareness, attitudes, preferences for risk information and decision-making concerning prenatal examinations with emphasis on NIPT, before its introduction into Swedish healthcare. METHOD: Pregnant women were recruited to fill in a questionnaire, including multiple-choice questions and Likert scales, at nine maternity clinics located in different areas of Stockholm, Sweden. RESULTS: In total, 1,003 women participated in the study (86% consent rate). The vast majority (90.7%) considered examinations aiming to detect fetal abnormalities to be good. Regarding NIPT, 59.8% stated that they had heard about the method previously, yet 74.0% would like to use the test if available. The main factor affecting the women's decision to undergo prenatal chromosomal screening was worry about the baby's health (82.5%), followed by the urge to have as much information as possible about the fetus (54.5%). Most women (79.9%) preferred to receive NIPT information orally. CONCLUSION: The overwhelming majority of a cohort of 1,003 pregnant women considered prenatal examinations good. Moreover, the majority had a positive attitude towards NIPT and would like to use the test if available.

CREBBP and EP300 mutational spectrum and clinical presentations in a cohort of Swedish patients with Rubinstein-Taybi syndrome.

Rubinstein-Taybi syndrome (RTS) is a rare autosomal dominant congenital disorder characterized by distinctive facial features, broad thumbs and halluces, growth retardation, and a variable degree of cognitive impairment. CREBBP is the major causative gene and mutations in EP300 are the cause of RTS in a minority of patients. In this study, 17 patients with a clinical diagnosis of RTS were investigated with direct sequencing, MLPA, and array-CGH in search for mutations in these two genes. Eleven patients (64.7%) had disease-causing point mutations or a deletion in CREBBP and in one patient (5.9%) a causal de novo frameshift mutation in EP300 was identified. This patient had broad thumbs, mild intellectual disability, and autism. In addition, an inherited missense mutation of uncertain clinical significance was identified in EP300 in one patient and his healthy father, and three patients had intronic nucleotide changes of uncertain clinical significance in CREBBP. Snoring and sleep apnea were common in both groups and four of the patients' mothers had preeclampsia during pregnancy. Importantly, difficulties associated with anesthesia were frequently reported and included delayed or complicated emergency in 53.3% of patients.

Rare copy number variants are common in young children with autism spectrum disorder.

AIM: Several studies have suggested that rare copy number variants (CNVs) are an important genetic contributor to autism spectrum disorders. The aims of the study were to use chromosomal microarray to investigate the presence of rare copy number variants in a population-based cohort of well-characterised young children with autism spectrum disorders and to relate the genetic results to neurodevelopmental profiles and medical conditions. METHODS: We performed chromosomal microarray on samples from 162 children who had been referred to the Stockholm Autism Centre for Young Children in Sweden after being diagnosed with autism spectrum disorder between 20 and 54 months of age. RESULTS: Pathogenic aberrations were detected in 8.6% of the children and variants of uncertain significance were present in another 8.6%. CNVs were more frequent in children with congenital malformations or dysmorphic features as well as in the subgroup with intellectual disability. CONCLUSION: Our results support the use of chromosomal microarray methods for the first tier genetic analysis of autism spectrum disorder. However, it is likely in the near future that chromosomal microarray methods will probably be replaced by whole-exome and whole-genome sequencing technologies in clinical genetic testing.

Copy number variations in children with brain malformations and refractory epilepsy.

Brain malformations are a major cause of therapy-refractory epilepsy as well as neurological and developmental disabilities in children. This study examined the frequency and the nature of copy number variations among children with structural brain malformations and refractory epilepsy. The medical records of all children born between 1990 and 2009 in the epilepsy registry at the Astrid Lindgren's Children's Hospital were reviewed and 86 patients with refractory epilepsy and various brain malformations were identified. Array-CGH analysis was performed in 76 of the patients. Pathogenic copy number variations were detected in seven children (9.2%). In addition, rearrangements of unclear significance, but possibly pathogenic, were detected in 11 (14.5%) individuals. In 37 (48.7%) patients likely benign, but previously unreported, copy number variants were detected. Thus, a large proportion of our patients had at least one rare copy number variant. Our results suggest that array-CGH should be considered as a first line genetic test for children with cerebral malformations and refractory epilepsy unless there is a strong evidence for a specific monogenic syndrome.

CHD7, the gene mutated in CHARGE syndrome, regulates genes involved in neural crest cell guidance.

Heterozygous loss of function mutations in CHD7 (chromodomain helicase DNA-binding protein 7) lead to CHARGE syndrome, a complex developmental disorder affecting craniofacial structures, cranial nerves and several organ systems. Recently, it was demonstrated that CHD7 is essential for the formation of multipotent migratory neural crest cells, which migrate from the neural tube to many regions of the embryo, where they differentiate into various tissues including craniofacial and heart structures. So far, only few CHD7 target genes involved in neural crest cell development have been identified and the role of CHD7 in neural crest cell guidance and the regulation of mesenchymal-epithelial transition are unknown. Therefore, we undertook a genome-wide microarray expression analysis on wild-type and CHD7 deficient (Chd7 (Whi/+) and Chd7 (Whi/Whi)) mouse embryos at day 9.5, a time point of neural crest cell migration. We identified 98 differentially expressed genes between wild-type and Chd7 (Whi/Whi) embryos. Interestingly, many misregulated genes are involved in neural crest cell and axon guidance such as semaphorins and ephrin receptors. By performing knockdown experiments for Chd7 in Xenopus laevis embryos, we found abnormalities in the expression pattern of Sema3a, a protein involved in the pathogenesis of Kallmann syndrome, in vivo. In addition, we detected non-synonymous SEMA3A variations in 3 out of 45 CHD7-negative CHARGE patients. In summary, we discovered for the first time that Chd7 regulates genes involved in neural crest cell guidance, demonstrating a new aspect in the pathogenesis of CHARGE syndrome. Furthermore, we showed for Sema3a a conserved regulatory mechanism across different species, highlighting its significance during development. Although we postulated that the non-synonymous SEMA3A variants which we found in CHD7-negative CHARGE patients alone are not sufficient to produce the phenotype, we suggest an important modifier role for SEMA3A in the pathogenesis of this multiple malformation syndrome.

Different mutations in PDE4D associated with developmental disorders with mirror phenotypes.

BACKGROUND: Point mutations in PDE4D have been recently linked to acrodysostosis, an autosomal dominant disorder with skeletal dysplasia, severe brachydactyly, midfacial hypoplasia and intellectual disability. The purpose of the present study was to investigate clinical and cellular implications of different types of mutations in the PDE4D gene. METHODS: We studied five acrodysostosis patients and three patients with gene dose imbalances involving PDE4D clinically and by whole exome sequencing, Sanger sequencing and array comparative hybridisation. To evaluate the functional consequences of the PDE4D changes, we used overexpression of mutated human PDE4D message and morpholino-based suppression of pde4d in zebrafish. RESULTS: We identified three novel and two previously described PDE4D point mutations in the acrodysostosis patients and two deletions and one duplication involving PDE4D in three patients suffering from an intellectual disability syndrome with low body mass index, long fingers, toes and arms, prominent nose and small chin. When comparing symptoms in patients with missense mutations and gene dose imbalances involving PDE4D, a mirror phenotype was observed. By comparing overexpression of human mutated transcripts with pde4d knockdown in zebrafish embryos, we could successfully assay the pathogenicity of the mutations. CONCLUSIONS: Our findings indicate that haploinsufficiency of PDE4D results in a novel intellectual disability syndrome, the 5q12.1-haploinsufficiency syndrome, with several opposing features compared with acrodysostosis that is caused by dominant negative mutations. In addition, our results expand the spectrum of PDE4D mutations underlying acrodysostosis and indicate that, in contrast to previous reports, patients with PDE4D mutations may have significant hormone resistance with consequent endocrine abnormalities.