KIF21B is a kinesin protein that promotes intracellular transport and controls microtubule dynamics. We report three missense variants and one duplication in KIF21B in individuals with ...neurodevelopmental disorders associated with brain malformations, including corpus callosum agenesis (ACC) and microcephaly. We demonstrate, in vivo, that the expression of KIF21B missense variants specifically recapitulates patients' neurodevelopmental abnormalities, including microcephaly and reduced intra- and inter-hemispheric connectivity. We establish that missense KIF21B variants impede neuronal migration through attenuation of kinesin autoinhibition leading to aberrant KIF21B motility activity. We also show that the ACC-related KIF21B variant independently perturbs axonal growth and ipsilateral axon branching through two distinct mechanisms, both leading to deregulation of canonical kinesin motor activity. The duplication introduces a premature termination codon leading to nonsense-mediated mRNA decay. Although we demonstrate that Kif21b haploinsufficiency leads to an impaired neuronal positioning, the duplication variant might not be pathogenic. Altogether, our data indicate that impaired KIF21B autoregulation and function play a critical role in the pathogenicity of human neurodevelopmental disorder.
Simultaneous analysis of multiple genes using next‐generation sequencing (NGS) technology has become widely available. Copy‐number variations (CNVs) in disease‐associated genes have emerged as a ...cause for several hereditary disorders. CNVs are, however, not routinely detected using NGS analysis. The aim of this study was to assess the diagnostic yield and the prevalence of CNVs using our panel of Hereditary Thoracic Aortic Disease (H‐TAD)‐associated genes. Eight hundred ten patients suspected of H‐TAD were analyzed by targeted NGS analysis of 21 H‐TAD associated genes. In addition, the eXome hidden Markov model (XHMM; an algorithm to identify CNVs in targeted NGS data) was used to detect CNVs in these genes. A pathogenic or likely pathogenic variant was found in 66 of 810 patients (8.1%). Of these 66 pathogenic or likely pathogenic variants, six (9.1%) were CNVs not detectable by routine NGS analysis. These CNVs were four intragenic (multi‐)exon deletions in MYLK, TGFB2, SMAD3, and PRKG1, respectively. In addition, a large duplication including NOTCH1 and a large deletion encompassing SCARF2 were detected. As confirmed by additional analyses, both CNVs indicated larger chromosomal abnormalities, which could explain the phenotype in both patients. Given the clinical relevance of the identification of a genetic cause, CNV analysis using a method such as XHMM should be incorporated into the clinical diagnostic care for H‐TAD patients.
The aim of this study was to assess the diagnostic yield and the prevalence of copy number variants in patients suspected of hereditary thoracic aortic disease (H‐TAD). A pathogenic or likely pathogenic variant was found in 66 of 810 patients (8.1%) and six out of these 66 likely pathogenic or pathogenic variants (9.1%) were copy number variants. Given the clinical relevance of identification of a genetic cause, copy number variant analysis should be incorporated into the clinical diagnostics of patients suspected of hereditary thoracic aortic disease.
Anterior segment dysgenesis (ASD) encompasses a broad spectrum of developmental conditions affecting anterior ocular structures and associated with an increased risk for glaucoma. Various systemic ...anomalies are often observed in ASD conditions such as Axenfeld-Rieger syndrome (ARS) and De Hauwere syndrome. We report DNA sequencing and copy number analysis of PITX2 and FOXC1 in 76 patients with syndromic or isolated ASD and related conditions. PITX2 mutations and deletions were found in 24 patients with dental and/or umbilical anomalies seen in all. Seven PITX2-mutant alleles were novel including c.708_730del, the most C-terminal mutation reported to date. A second case of deletion of the distant upstream but not coding region of PITX2 was identified, highlighting the importance of this recently discovered mechanism for ARS. FOXC1 deletions were observed in four cases, three of which demonstrated hearing and/or heart defects, including a patient with De Hauwere syndrome; no nucleotide mutations in FOXC1 were identified. Review of the literature identified several other patients with 6p25 deletions and features of De Hauwere syndrome. The 1.3-Mb deletion of 6p25 presented here defines the critical region for this phenotype and includes the FOXC1, FOXF2, and FOXQ1 genes. In summary, PITX2 or FOXC1 disruptions explained 63% of ARS and 6% of other ASD in our cohort; all affected patients demonstrated additional systemic defects with PITX2 mutations showing a strong association with dental and/or umbilical anomalies and FOXC1 with heart and hearing defects. FOXC1 deletion was also found to be associated with De Hauwere syndrome.
Lysine‐specific demethylase 6B (KDM6B) demethylates trimethylated lysine‐27 on histone H3. The methylation and demethylation of histone proteins affects gene expression during development. Pathogenic ...alterations in histone lysine methylation and demethylation genes have been associated with multiple neurodevelopmental disorders. We have identified a number of de novo alterations in the KDM6B gene via whole exome sequencing (WES) in a cohort of 12 unrelated patients with developmental delay, intellectual disability, dysmorphic facial features, and other clinical findings. Our findings will allow for further investigation in to the role of the KDM6B gene in human neurodevelopmental disorders.
Mutations in COL4A1 have been identified in families with hereditary small vessel disease of the brain presumably due to a dominant-negative mechanism. Here, we report on two novel mutations in ...COL4A1 in two families with porencephaly, intracerebral hemorrhage and severe white matter disease caused by haploinsufficiency. Two families with various clinical presentations of cerebral microangiopathy and autosomal dominant inheritance were examined. Clinical, neuroradiological and genetic investigations were performed. Electron microscopy of the skin was also performed. In one of the families, sequence analysis revealed a one base deletion, c.2085del, leading to a frameshift and a premature stopcodon, p.(Gly696fs). In the other family, a splice site mutation was identified, c.2194-1G>A, which most likely leads to skipping of an exon with a frameshift and premature termination as a result. In fibroblasts of affected individuals from both the families, nonsense-mediated decay (NMD) of the mutant COL4A1 messenger RNAs (mRNAs) and a clear reduction of COL4A1 protein expression were demonstrated, indicating haploinsufficiency of COL4A1. Moreover, thickening of the capillary basement membrane in the skin was documented, similar to reports in patients with COL4A1 missense mutations. These findings suggest haploinsufficiency, a different mechanism from the commonly assumed dominant-negative effect, for COL4A1 mutations as a cause of (antenatal) intracerebral hemorrhage and white matter disease.
Copy number variations associate with different developmental phenotypes and represent a major cause of congenital anomalies of the kidney and urinary tract (CAKUT). Because rare pathogenic copy ...number variations are often large and contain multiple genes, identification of the underlying genetic drivers has proven to be difficult. Here we studied the role of rare copy number variations in 80 patients from the KIMONO study cohort for which pathogenic mutations in three genes commonly implicated in CAKUT were excluded. In total, 13 known or novel genomic imbalances in 11 of 80 patients were absent or extremely rare in 23,362 population controls. To identify the most likely genetic drivers for the CAKUT phenotype underlying these rare copy number variations, we used a systematic in silico approach based on frequency in a large data set of controls, annotation with publicly available databases for developmental diseases, tolerance and haploinsufficiency scores, and gene expression profile in the developing kidney and urinary tract. Five novel candidate genes for CAKUT were identified that showed specific expression in the human and mouse developing urinary tract. Among these genes, DLG1 and KIF12 are likely novel susceptibility genes for CAKUT in humans. Thus, there is a significant role of genomic imbalance in the determination of kidney developmental phenotypes. Additionally, we defined a systematic strategy to identify genetic drivers underlying rare copy number variations.
In children with anorectal malformations (ARM), additional anomalies can occur within the VACTERL-association. Routine screening is of great importance for early identification and potential ...treatment. However, uniformity in screening protocols is lacking and only small cohorts have been described in literature. The aim of this study was to assess and describe a unique large cohort of ARM patients who underwent VACTERL screening in the neonatal period.
A retrospective mono-center cohort study was performed. Included were all neonates born between January 2000 and December 2020 who were diagnosed with ARM and screened for additional anomalies. Full screening consisted of x-ray and ultrasound of the spine, cardiac and renal ultrasound, and physical examination for limb deformities, esophageal atresia, and ARM. Criteria for VACTERL-classification were predefined according to the EUROCAT-definitions.
In total, 216 patients were included, of whom 167 (77.3%) underwent full VACTERL-screening (66% in 2000–2006 vs. 82% in 2007–2013 vs. 86% in 2014–2020). Median age at follow-up was 7.0 years (IQR 3.0–12.8). In 103/167 patients (61.7%), additional anomalies were identified. Some 35/216 patients (16.2%) fulfilled the criteria of a form of VACTERL-association. In 37/216 patients (17.1%), a genetic cause or syndrome was found.
The majority of ARM patients underwent full screening to detect additional anomalies (77%), which improved over time to 86%. Yet, approximately a quarter of patients was not screened, with the potential of missing important additional anomalies that might have severe consequences in the future. Forms of VACTERL-association or genetic causes were found in 16% and 17% respectively. This study emphasizes the importance of routine screening.
III.
•ARM can occur as isolated anomaly, or as part of VACTERL-association or syndromes. Additional anomalies can occur.•62% of the ARM patients had additional anomalies. VACTERL-association or syndromes were found in 16% and 17% respectively.
Duodenal obstruction (DO) is a congenital anomaly that is highly associated with other anomalies, such as cardiac anomalies and trisomy 21. However, an overview of additional anomalies and ...patient-specific risk factors for cardiac anomalies is lacking. Potential association with the vertebral, anorectal, cardiac, trachea-esophageal, renal and limb anomalies (VACTERL) spectrum remains unknown. Therefore, we aim to examine the incidence of associated anomalies, a VACTERL-spectrum association and patient-specific risk factors for cardiac anomalies in patients with DO.
A retrospective cohort study was performed between 1996 and 2021. Outcomes were the presence of any additional anomalies. Risk factors for cardiac anomalies were analyzed using multivariate logistic regression.
Of 112 neonates with DO, 47% (N = 53/112) had one associated anomaly and 38% (N = 20/53) had multiple anomalies. Cardiac anomalies (N = 35/112) and trisomy 21 (N = 35/112) were present in 31%. In four patients, VACTERL-spectrum was discovered, all with cardiac anomalies. Trisomy 21 was found to be a risk factor for cardiac anomalies (OR:6.5; CI-95%2.6-16.1).
Associated anomalies were present in half of patients with DO, of which cardiac anomalies and trisomy 21 occurred most often, and the VACTERL-spectrum was present in four patients. Trisomy 21 was a significant risk factor for cardiac anomalies. Therefore, we recommend a preoperative echocardiogram in patients with DO. In case a cardiac anomaly is found without trisomy 21, VACTERL-screening should be performed.
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