Clinical and Genetic Characteristics of Patients with Unexplained Intellectual Disability/Developmental Delay without Epilepsy

Novel mutations found in genes involved in global developmental delay and intellectual disability by whole-exome sequencing, homology modeling, and systems biology

BACKGROUND

Genes associated with global developmental delay (GDD) and intellectual disability (ID) are increasingly being identified through next-generation sequencing (NGS) technologies. This study aimed to identify novel mutations in GDD/ID phenotypes through whole-exome sequencing (WES) and additional in silico analyses.

MATERIAL AND METHODS

WES was performed on 27 subjects, among whom 18 were screened for potential novel mutations. In silico analyses included protein-protein interactions (PPIs), gene-miRNA interactions (GMIs), and enrichment analyses. The identified novel variants were further modelled using I-Tasser-MTD and SWISS-MODEL, with structural superimposition performed.

RESULTS

Novel mutations were detected in 18 patients, with 10 variants reported for the first time. Among these, three were classified as pathogenic (DNMT1:c.856dup, KCNQ2:c.1635_1636insT, and TMEM94:c.2598_2599insC), and six were likely pathogenic. DNMT1 and MRE11 were highlighted as key players in PPIs and GMIs. GMIs analysis emphasised the roles of hsa-miR-30a-5p and hsa-miR-185-5p. The top-scoring pathways included the neuronal system (R-HSA-112316, p = 7.73E-04) and negative regulation of the smooth muscle cell apoptotic process (p = 3.37E-06). Homology modelling and superimposition revealed a significant functional loss in the mutated DNMT1 enzyme structure.

CONCLUSION

This study identified 10 novel pathogenic/likely pathogenic variants associated with GDD/ID, supported by clinical findings and in silico analyses focused on DNMT1 mutations.

Exome sequencing in 90 children with developmental delay: a single-center experience

Introduction

Developmental delay (DD) in children is often caused by genetic abnormalities, which are challenging to diagnose due to the vast genetic variability.

Methods

This study presents a detailed analysis of whole-exome sequencing (WES) on 90 children with DD at a single clinical center.

Results

We identified pathogenic or likely pathogenic variants in 27.8% of cases, with 7.8% revealing variants of uncertain significance (VUS). Among the positive findings, 21 (84.0%) corresponded to the main clinical manifestations in patients, and 4 (16.0%) secondary findings provided new insights into the patient's conditions. Positive and inconclusive cases led to a revision of the diagnosis or management plan in 34.4% of cases. The positive genetic result in children with Developmental delay was higher in the presence of epilepsy or seizures (odds ratio - 5.4444; 95% CI 2.0176 to 14.6918; p = 0.0008) and more than 3 dysmorphic features (odds ratio - 7.1739; 95% CI 1.7791 to 28.9282; p = 0.0056). Variants compatible with the clinical manifestations were identified in 11.9% of children with autistic spectrum disorders.

Conclusion

Our findings emphasize the utility of WES in clinical diagnostics, offering significant insights into patient management and potentially guiding therapeutic decisions.

A novel heterozygous TMEM63A variant in a familial case with early onset nystagmus, severe hypomyelination, and a favorable adult prognosis

Heterozygous transmembrane protein 63A (TMEM63A) variants cause transient infantile hypomyelinating leukodystrophy-19, which features remarkable natural resolution of clinical and imaging findings during childhood. Previous reports have mainly described de novo variants lacking detailed familial cases. Herein, we describe the clinical course of familial cases with a TMEM63A variant. A 5-month-old girl presented with nystagmus, global hypotonia, and difficulty swallowing since birth. Brain magnetic resonance imaging at 1.5 and 5 months revealed diffuse hypomyelination. Her mother, maternal aunt, and grandfather had nystagmus and motor developmental delays in infancy, which resolved spontaneously during childhood. Compared with these cases, the proband's motor developmental delay was profound, and she was the only one with feeding difficulties, necessitating nasogastric tube feeding. Genetic testing revealed a heterozygous TMEM63A variant (NM_014698.3:c.1658G>A, p.(Gly553Asp)) in the proband and her family. This is the first three-generation familial report of a TMEM63A variant that provides insight into its history and heterogeneity.

Rare heterozygous genetic variants of NRXN and NLGN gene families involved in synaptic function and their association with neurodevelopmental disorders

The interaction of neurexins (NRXNs) in the presynaptic membrane with postsynaptic cell adhesion molecules called neuroligins (NLGNs) is critical for this synaptic function. Impaired synaptic functions are emphasized in neurodevelopmental disorders to uncover etiological factors. We evaluated variants in NRXN and NLGN genes encoding molecules located directly at the synapse in patients with neuropsychiatric disorders using clinical exome sequencing and chromosomal microarray. We presented detailed clinical findings of cases carrying heterozygous NRXN1 (c.190C > T, c.1679C > T and two copy number variations [CNVs]), NRXN2 (c.808dup, c.1901G > T), NRXN3 (c.3889C > T), and NLGN1 (c.269C > G, c.473T > A) gene variants. In addition, three novel variants were identified in the NRXN1 (c.1679C > T), NRXN3 [c.3889C > T (p.Pro1297Ser)], and NLGN1 [c.473T > A (p.Ile158Lys)] genes. We emphasize the clinical findings of CNVs of the NRXN1 gene causing a more severe clinical presentation than single nucleotide variants of the NRXN1 gene in this study. We detected an NRXN2 gene variant (c.808dup) with low allelic frequency in two unrelated cases with the same diagnosis. We emphasize the importance of this variant for future studies. We suggest that NRXN2, NRXN3, and NLGN1 genes, which are less frequently reported than NRXN1 gene variants, may also be associated with neurodevelopmental disorders.

Association of ABCA13 Gene Variants with Autism Spectrum Disorder and Other Neuropsychiatric Disorders

Introduction

Autism spectrum disorder (ASD) is a neuropsychiatric disorder characterized by impaired social skills and limited or repetitive behaviors. In this study, we investigated the role of the ABCA13 gene in the etiopathogenesis of ASD.

Methods

Single-nucleotide variants were evaluated in 79 ASD patients (59 males +20 females) with no established genetic etiology associated with ASD using whole-exome sequencing/clinical exome sequencing method. Family segregation analysis was performed using Sanger sequencing. We presented the clinical and genetic findings of these cases and their parents in detail.

Results

We presented 10 different ABCA13 gene variants in cases with ASD and 10 parents carrying the same ABCA13 gene variant. There of these variants were likely pathogenic and seven variants were classified as variant of uncertain significance. Our cases had a comorbidity rate for attention deficit hyperactivity disorder (ADHD) as 70%. Various types of neuropsychiatric symptoms and diagnoses were detected including ADHD, anxiety disorder, intellectual disability, delay in speech, and febrile convulsion among the parents.

Conclusion

To date, very few variants have been reported in the ABCA13 gene. Our findings enrich the role of ABCA13 gene may play a common role in the landscape of neuropsychiatric disorders.

TMEM63 mechanosensitive ion channels: Activation mechanisms, biological functions and human genetic disorders

The transmembrane 63 (TMEM63) family of proteins are originally identified as homologs of the osmosensitive calcium-permeable (OSCA) channels in plants. Mechanosensitivity of OSCA and TMEM63 proteins are recently demonstrated in addition to their proposed activation mechanism by hyper/hypo-osmolarity. TMEM63 proteins exist in all animals, with a single member in Drosophila (TMEM63) and three members in mammals (TMEM63 A/B/C). In humans, monoallelic variants of TMEM63A have been reported to cause transient hypomyelination during infancy, or severe hypomyelination and global developmental delay. Heterozygous variants of TMEM63B are found in patients with intellectual disability and abnormal motor function and brain morphology. Biallelic variants of TMEM63C are associated with hereditary spastic paraplegias accompanied by mild or no intellectual disability. Physiological functions of TMEM63 proteins clearly recognized so far include detecting food grittiness and environmental humidity in Drosophila, and supporting hearing in mice by regulating survival of cochlear hair cells. In this review, we summarize current knowledge about the activation mechanisms and biological functions of TMEM63 channels, and provide a concise reference for researchers interested in investigating more physiological and pathogenic roles of this family of proteins with ubiquitous expression in the body.