Biology subjects

Ansar, M.

Publications and source records attributed to Ansar, M..

6 recordsLinked to original sources

bioRxiv2025

Lipid transport is necessary for neocortical lamination

We previously described the Alkuraya-Ku[c]inskas syndrome, a disorder associated with biallelic variants in BLTP1 (bridge-like lipid transfer protein), a.k.a. KIAA1109. The majority of probands die perinatally with corpus callosum agenesis, ventriculomegaly and arthrogryposis. Homozygous ablation of mouse Bltp1 resulted in similar preweaning lethality. Here, we describe ten novel patients expanding the characterization of this syndrome at the mild end of the phenotypic spectrum. To model this syndrome, we engineered Emx1-Cre-mediated conditional knockouts (cKO) in which Bltp1 expression is only removed in cortical and hippocampal neurons. This restricted ablation of Bltp1 recapitulated the preweaning lethality observed in the constitutional knockouts, suggesting that lack of BLTP1 expression in neurons is sufficient to cause death. Homozygous cKO presented a complete agenesis of the corpus callosum, a smaller anterior commissure, a malformed hippocampus and a reduced thickness of the cortical plate with a complete lack of defined structural layers and absence of radial glial and intermediate neural progenitors and mature neurons. As BLTP1 was shown to be a barrel-shaped tube containing lipids, we compared the amount of lipid species in the cKO and their control littermates cortexes. We observed significant depletions of ether-linked phosphatidylethanolamines and triglycerides and accumulations of sphingomyelins and hexosylceramides in cKOs. Our results are consistent with the recent description of BLTP1 as a tubular protein that transports phospholipids between the endoplasmic reticulum and the plasma membrane. They suggest that non-vesicular lipid transport is essential for neocortical and cerebellar lamination. Consistent with a BLTP1 role in cortex development we show that heterozygous carriers of a BLTP1 truncation variant presented a decrease in peripheral cortical grey matter suggesting an autosomal dominant inheritance pattern beside the already described autosomal recessive.

genetics↗

bioRxiv2025

Lysosome-Dependent Sphingolipid Regulation as a potential therapeutic Target for Cohen Syndrome

Cohen Syndrome (CS) is a rare autosomal recessive disorder caused by biallelic mutations in the VPS13B gene, affecting approximately 50,000 individuals worldwide. Clinical features include postnatal microcephaly, developmental delay, intellectual disability, neutropenia, and retinal dystrophy. VPS13B belongs to the bridge-like lipid transfer protein (BLTP) family, which also includes VPS13A, VPS13C, and VPS13D in mammals. Although its precise function remains unclear, VPS13B localizes to the Golgi complex, and its loss leads to Golgi fragmentation, a consistent cellular phenotype observed in VPS13B-deficient models. We used the rescue of this cell-autonomous phenotype as the basis for a microscopy-based high-throughput screening assay, through which we identified several small molecules capable of restoring Golgi morphology. Most of these compounds shared a common mechanism of action, relying on lipid accumulation in acidic organelles due to their cationic amphiphilic properties (CADs). Lipidomic profiling revealed a reduction in C18-N-acyl sphingolipids as a characteristic feature of VPS13B knockout (KO) cells, a defect that was reversed by the majority of the identified compounds. To evaluate the physiological relevance of these findings, we tested two compounds, azelastine and raloxifene, in cortical organoids (COs) derived from VPS13B KO human pluripotent stem cells. These organoids exhibited smaller size and reduced neurite outgrowth, reminiscent of the secondary microcephaly observed in CS patients. Treatment with either compound significantly recovered the neurite outgrowth phenotype, reinforcing physiological relevance of the compound effect. Taken together, our findings highlight a potential effect of the CAD on lysosome-dependent sphingolipid regulation, allowing the recovery of Golgi integrity and partial rescue in the cortical organoid CS model. Although additional studies are required to delineate the exact molecular targets, this work uncovers a potential mechanism that could be leveraged for the treatment of CS.

cell biology↗

bioRxiv2025

Characterization of Human Anterior Neural Organoids as a Model for Investigating Cohen Syndrome

Neural organoids display three-dimensional (3D) structures that resemble in vivo neural architectures. Previously, we developed a novel two-dimensional (2D) neural induction-based protocol for culturing spinal cord organoids, enabling size control and recapitulating neural tube morphogenesis. In this study, we evaluated the application of this concept to induce the anterior regions of the brain and generate human anterior neural organoids (hANOs). By inducing neuroepithelial (NE) cells in 2D and re-aggregating them led to tube-forming morphogenesis similar to that posterior spinal cord induction. The transcriptome profiles of these hANOs resembled the frontal cortex of 20 weeks post-conception (PCW) human embryos. Using this hANOs protocol, we investigated microcephaly phenotypes associated with Cohen syndrome (CS), caused by biallelic loss-of-function variants in VPS13B gene. Deleting VPS13B in human pluripotent stem cells resulted in Golgi dispersion and growth retardation onset in mutant hANOs, akin to CS patients with postnatal microcephaly. This delay is partly linked to reduced neuronal growth. Additionally, mature CS organoids showed enhanced hyper-excitability associated with an excitatory/inhibitory imbalance. In conclusion, this protocol is suitable for studying microcephaly phenotypes from human genetic mutations due to its simplicity and scalability.

neuroscience↗

bioRxiv2020

Dominant monoallelic variant in the PAK2 gene causes Knobloch syndrome type 2

Knobloch syndrome is an autosomal recessive phenotype mainly characterized by retinal detachment and encephalocele caused by biallelic pathogenic variants in the COL18A1 gene. However, there are patients clinically diagnosed as Knobloch syndrome with unknown molecular etiology not linked to COL18A1. We studied an historical pedigree (published in 1998) designated as KNO2 (Knobloch type 2 syndrome with intellectual disability, autistic behavior, retinal degeneration, encephalocele). Whole exome sequencing of the two affected siblings and the normal parents resulted in the identification of a PAK2 non-synonymous substitution p.(Glu435Lys) as a causative variant. The variant was monoallelic and apparently de novo in both siblings indicating a likely germline mosaicism in one of the parents; the mosaicism however could not be observed after deep sequencing of blood parental DNA. PAK2 encodes a member of a small group of serine/threonine kinases; these P21-activating kinases (PAKs) are essential in signal transduction and cellular regulation (cytoskeletal dynamics, cell motility, death and survival signaling, and cell cycle progression). Structural analysis of the PAK2 p.(Glu435Lys) variant which is located in the kinase domain of the protein predicts a possible compromise in the kinase activity. Functional analysis of the p.(Glu435Lys) PAK2 variant in transfected HEK293T cells results in a partial loss of the kinase activity. PAK2 has been previously suggested as an autism related gene. Our results show that PAK2 induced phenotypic spectrum is broad and not fully understood. We conclude that the KNO2 syndrome in the studied family is dominant and caused by a deleterious variant in the PAK2 gene.

genetics↗

bioRxiv2019

Delineation of the First Human Mendelian Disorder of the DNA Demethylation Machinery: TET3 Deficiency

Germline pathogenic variants in chromatin-modifying enzymes are a common cause of pediatric developmental disorders. These enzymes catalyze reactions that regulate epigenetic inheritance via histone post-translational modifications and DNA methylation. Cytosine methylation of DNA (5mC) is the quintessential epigenetic mark, yet no human Mendelian disorder of DNA demethylation has been delineated. Here, we describe in detail the first Mendelian disorder caused by disruption of DNA demethylation. TET3 is a methylcytosine dioxygenase that initiates DNA demethylation during early zygote formation, embryogenesis, and neuronal differentiation and is intolerant to haploinsufficiency in mice and humans. Here we identify and characterize 11 cases of human TET3 deficiency in 8 families with the common phenotypic features of intellectual disability/global developmental delay, hypotonia, autistic traits, movement disorders, growth abnormalities, and facial dysmorphism. Mono-allelic frameshift and nonsense variants in TET3 occur throughout the coding region. Mono-allelic and bi-allelic missense variants localize to conserved residues with all but one occurring within the catalytic domain and most displaying hypomorphic function in a catalytic activity assay. TET3 deficiency shows substantial phenotypic overlap with other Mendelian disorders of the epigenetic machinery, including intellectual disability and growth abnormalities, underscoring shared disease mechanisms.

genetics↗

bioRxiv2016

Mapping Autosomal Recessive Intellectual Disability: Combined Microarray and Exome Sequencing Identifies 26 Novel Candidate Genes in 192 Consanguineous Families

Approximately 1% of the global population is affected by intellectual disability (ID), and the majority receive no molecular diagnosis. Previous studies have indicated high levels of genetic heterogeneity, with estimates of more than 2500 autosomal ID genes, the majority of which are autosomal recessive (AR). Here, we combined microarray genotyping, homozygosity-by-descent (HBD) mapping, copy number variation (CNV) analysis, and whole exome sequencing (WES) to identify disease genes/mutations in 192 multiplex Pakistani and Iranian consanguineous families with non-syndromic ID. We identified definite or candidate mutations (or CNVs) in 51% of families in 72 different genes, including 26 not previously reported for ARID. The new ARID genes include nine with loss-of-function mutations (ABI2, MAPK8, MPDZ, PIDD1, SLAIN1, TBC1D23, TRAPPC6B, UBA7, and USP44), and missense mutations include the first reports of variants in BDNF or TET1 associated with ID. The genes identified also showed overlap with de novo gene sets for other neuropsychiatric disorders. Transcriptional studies showed prominent expression in the prenatal brain. The high yield of AR mutations for ID indicated that this approach has excellent clinical potential and should inform clinical diagnostics, including clinical whole exome and genome sequencing, for populations in which consanguinity is common. As with other AR disorders, the relevance will also apply to outbred populations.

genetics↗