Novel MYO1D Missense Variant Identified Through Whole Exome Sequencing and Computational Biology Analysis Expands the Spectrum of Causal Genes of Laterality Defects

Myosin1G promotes Nodal signaling to control zebrafish left-right asymmetry

Myosin1D (Myo1D) has recently emerged as a conserved regulator of animal Left-Right (LR) asymmetry that governs the morphogenesis of the vertebrate central LR Organizer (LRO). In addition to Myo1D, the zebrafish genome encodes the closely related Myo1G. Here we show that while Myo1G also controls LR asymmetry, it does so through an entirely different mechanism. Myo1G promotes the Nodal-mediated transfer of laterality information from the LRO to target tissues. At the cellular level, Myo1G is associated with endosomes positive for the TGFβ signaling adapter SARA. myo1g mutants have fewer SARA-positive Activin receptor endosomes and a reduced responsiveness to Nodal ligands that results in a delay of left-sided Nodal propagation and tissue-specific laterality defects in organs that are most distant from the LRO. Additionally, Myo1G promotes signaling by different Nodal ligands in specific biological contexts. Our findings therefore identify Myo1G as a context-dependent regulator of the Nodal signaling pathway.

Identification of a novel MYO1D variant associated with laterality defects, congenital heart diseases, and sperm defects in humans

The establishment of left-right asymmetry is a fundamental process in animal development. Interference with this process leads to a range of disorders collectively known as laterality defects, which manifest as abnormal arrangements of visceral organs. Among patients with laterality defects, congenital heart diseases (CHD) are prevalent. Through multiple model organisms, extant research has established that myosin-Id (MYO1D) deficiency causes laterality defects. This study investigated over a hundred cases and identified a novel biallelic variant of MYO1D (NM_015194: c.1531G>A; p.D511N) in a consanguineous family with complex CHD and laterality defects. Further examination of the proband revealed asthenoteratozoospermia and shortened sperm. Afterward, the effects of the D511N variant and another known MYO1D variant (NM_015194: c.2293C>T; p.P765S) were assessed. The assessment showed that both enhance the interaction with β-actin and SPAG6. Overall, this study revealed the genetic heterogeneity of this rare disease and found that MYO1D variants are correlated with laterality defects and CHD in humans. Furthermore, this research established a connection between sperm defects and MYO1D variants. It offers guidance for exploring infertility and reproductive health concerns. The findings provide a critical basis for advancing personalized medicine and genetic counseling.

Movement Asymmetries: From Their Molecular Origin to the Analysis of Movement Asymmetries in Athletes

Asymmetry plays a major role in biology at all scales. This can be seen in the helix of DNA, the fact that the human heart is on the left side, or that most people use their right hand. A single protein such as Myosin 1D can induce helical motion in another molecule. This causes cells, organs, and even entire bodies to twist in a domino effect, causing left-right behaviour. More generally, athlete movements are often asymmetric and, during the physical rehabilitation after injury, the asymmetry is visually discernible. Herein, we review the molecular basis of the movement asymmetries and report on the available knowledge on the few therapeutics investigated so far such as meloxicam. From a more rehabilitative perspective, it is very important to use effective methods to control the process of resolving the injury-related movement asymmetry through the complex use of specialised exercises, measurements, and gait analysis, which can all provide useful information on the effectiveness of the rehabilitation plans. If for each athlete, the normal range of asymmetry is known, the asymmetry can be individually treated and the evolution can be monitored over time. Appropriate measures should be taken if the movement asymmetry is outside this range. In addition, genetic, physiological, and psychological factors relevant to athlete health should be considered in the process of assessing and improving exercise asymmetry, which we also discuss in this review. The main proposal of this work is that the movement asymmetries in athletes should be individually treated, while taking into account the athlete's genetics, physical condition, and previous injuries.

Computational biology insights into genotype-clinical phenotype-protein phenotype relationships between novel SLC26A2 variants identified in inherited skeletal dysplasias

BACKGROUND

Pathogenic variants in the transmembrane sulfate transporter protein SLC26A2 are associated with different phenotypes of inherited chondrodysplasias. As limited data is published from India, in this study we sought to elucidate the molecular basis of inherited chondrodysplasias in an Indian cohort.

METHODS

Molecular screening of 32 fetuses with antenatally diagnosed lethal skeletal dysplasia was performed by next generation sequencing and Sanger sequencing. The genotype-protein phenotype characterization was done using computational biology techniques like homology modelling, stability and pathogenicity predictions.

RESULTS

We identified five rare autosomal recessive SLC26A2 [NM_000112.4] variants, including three homozygous c.796dupA(p.Thr266Asnfs*12), c.1724delA(p.Lys575Serfs*10), and c.1375_1377dup(p.Val459dup) and two heterozygous variants (c.532C > T(p.Arg178*)) and (c.1382C > T(p.Ala461Val)) in compound heterozygous form in a total of four foetuses. Genotype-protein phenotype annotations highlighted that the clinically severe achondrogenesis 1B causative c.796dupA(p.Thr266Asnfs*12) and c.1724delA(p.Lys575Serfs*10)variants impact SLC26A2 protein structure by deletion of the protein core and transmembrane STAS domains, respectively. In clinically moderate atelosteogenesis type 2 phenotype, the c.1382C > T(p.Ala461Val) variant is predicted to distort alpha helix conformation and alter the bonding properties and free energy dynamics of transmembrane domains and the c.532C > T(p.Arg178*) variant results in loss of both core transmembrane and STAS domains of the SLC26A2 protein. The c.1375_1377dup(p.Val459dup) variant identified in clinically milder atelosteogenesis type II-diastrophic dysplasia spectrum lethal phenotype is predicted to decrease the Qualitative Model Energy Analysis (QMean), which affects major geometrical aspects of the SLC26A2 protein structure.

CONCLUSION

We expand the spectrum of SLC26A2 related lethal chondrodysplasia and report three novel variants correlating clinical severity and protein phenotype within the lethal spectrum of this rare dysplasia. We demonstrate the relevance of structural characterization to aid novel variant reclassification to provide better prenatal management and reproductive options to families with lethal antenatal skeletal disorder.

Granulomatous hepatitis in a Saudi child with IL2RA defect: a case report and literature review

Interleukin-2 receptor alpha (IL2RA) defect (OMIM- # 606367) is an immune disease where affected patients are vulnerable to developing recurrent microbial infections in addition to lymphadenopathy and dermatological manifestations. This condition is known to be caused by pathogenic variants in the IL2RA gene, which are inherited in an autosomal recessive fashion. In this case report, we present a patient with IL2RA defect from Saudi Arabia who presented with chronic diarrhea, poor weight gain, mild villous atrophy, malnutrition, hepatomegaly, nonspecific inflammation, and an eczematous skin rash. His genetic analysis revealed a novel, homozygous, and likely pathogenic variant, that is, c.504 C>A (Cys168Ter), located in the exon 4of the IL2RA gene, which was inherited from his parents in an autosomal recessive mode of inheritance. This variant produces a 272-amino-acid shorter IL2RA protein chain, which most likely becomes degraded in the cytosol. Thus, we assume that the c.504 C>A is a null allele that abolishes the synthesis of IL2RA, malforms the IL-2 receptor complex, and eventually causes immunodeficiency manifestations. To our knowledge, this is the first time a person with IL2RA defect has shown signs of granulomatous hepatitis on a liver biopsy.

The genetic landscape of cardiovascular left-right patterning defects

Heterotaxy is a disorder with complex congenital heart defects and diverse left-right (LR) patterning defects in other organ systems. Despite evidence suggesting a strong genetic component in heterotaxy, the majority of molecular causes remain unknown. Established genes often involve a ciliated, embryonic structure known as the left-right organizer (LRO). Herein, we focus on genetic discoveries in heterotaxy in the past two years. These include complex genetic architecture, novel mechanisms regulating cilia formation, and evidence for conservation of LR patterning between distant species. We feature new insights regarding established LR signaling pathways, bring attention to heterotaxy candidate genes in novel pathways, and provide an extensive overview of genes previously associated with laterality phenotypes in humans.