The role of HCFC1 in syndromic and non-syndromic intellectual disability

O-GlcNAc transferase congenital disorder of glycosylation (OGT-CDG): Potential mechanistic targets revealed by evaluating the OGT interactome

O-GlcNAc transferase (OGT) is the sole enzyme responsible for the post-translational modification of O-GlcNAc on thousands of target nucleocytoplasmic proteins. To date, nine variants of OGT that segregate with OGT Congenital Disorder of Glycosylation (OGT-CDG) have been reported and characterized. Numerous additional variants have been associated with OGT-CDG, some of which are currently undergoing investigation. This disorder primarily presents with global developmental delay and intellectual disability (ID), alongside other variable neurological features and subtle facial dysmorphisms in patients. Several hypotheses aim to explain the etiology of OGT-CDG, with a prominent hypothesis attributing the pathophysiology of OGT-CDG to mutations segregating with this disorder disrupting the OGT interactome. The OGT interactome consists of thousands of proteins, including substrates as well as interactors that require noncatalytic functions of OGT. A key aim in the field is to identify which interactors and substrates contribute to the primarily neural-specific phenotype of OGT-CDG. In this review, we will discuss the heterogenous phenotypic features of OGT-CDG seen clinically, the variable biochemical effects of mutations associated with OGT-CDG, and the use of animal models to understand this disorder. Furthermore, we will discuss how previously identified OGT interactors causal for ID provide mechanistic targets for investigation that could explain the dysregulated gene expression seen in OGT-CDG models. Identifying shared or unique altered pathways impacted in OGT-CDG patients will provide a better understanding of the disorder as well as potential therapeutic targets.

Variants in HCFC1 and MN1 genes causing intellectual disability in two Pakistani families

BACKGROUND

Intellectual disability (ID) is a neurodevelopmental condition affecting around 2% of children and young adults worldwide, characterized by deficits in intellectual functioning and adaptive behavior. Genetic factors contribute to the development of ID phenotypes, including mutations and structural changes in chromosomes. Pathogenic variants in the HCFC1 gene cause X-linked mental retardation syndrome, also known as Siderius type X-linked mental retardation. The MN1 gene is necessary for palate development, and mutations in this gene result in a genetic condition called CEBALID syndrome.

METHODS

Exome sequencing was used to identify the disease-causing variants in two affected families, A and B, from various regions of Pakistan. Affected individuals in these two families presented ID, developmental delay, and behavioral abnormalities. The validation and co-segregation analysis of the filtered variant was carried out using Sanger sequencing.

RESULTS

In an X-linked family A, a novel hemizygous missense variant (c.5705G > A; p.Ser1902Asn) in the HCFC1 gene (NM_005334.3) was identified, while in family B exome sequencing revealed a heterozygous nonsense variant (c.3680 G > A; p. Trp1227Ter) in exon-1 of the MN1 gene (NM_032581.4). Sanger sequencing confirmed the segregation of these variants with ID in each family.

CONCLUSIONS

The investigation of two Pakistani families revealed pathogenic genetic variants in the HCFC1 and MN1 genes, which cause ID and expand the mutational spectrum of these genes.

Neurodevelopmental defects in a mouse model of O-GlcNAc transferase intellectual disability

The addition of O-linked β-N-acetylglucosamine (O-GlcNAc) to proteins (referred to as O-GlcNAcylation) is a modification that is crucial for vertebrate development. O-GlcNAcylation is catalyzed by O-GlcNAc transferase (OGT) and reversed by O-GlcNAcase (OGA). Missense variants of OGT have recently been shown to segregate with an X-linked syndromic form of intellectual disability, OGT-linked congenital disorder of glycosylation (OGT-CDG). Although the existence of OGT-CDG suggests that O-GlcNAcylation is crucial for neurodevelopment and/or cognitive function, the underlying pathophysiologic mechanisms remain unknown. Here we report a mouse line that carries a catalytically impaired OGT-CDG variant. These mice show altered O-GlcNAc homeostasis with decreased global O-GlcNAcylation and reduced levels of OGT and OGA in the brain. Phenotypic characterization of the mice revealed lower body weight associated with reduced body fat mass, short stature and microcephaly. This mouse model will serve as an important tool to study genotype-phenotype correlations in OGT-CDG in vivo and for the development of possible treatment avenues for this disorder.

LPCAT1 enhances the invasion and migration in gastric cancer: Based on computational biology methods and in vitro experiments

BACKGROUND AND AIM

The biological functions and clinical implications of lysophosphatidylcholine acyltransferase 1 (LPCAT1) remain unclarified in gastric cancer (GC). The aim of the current study was to explore the possible clinicopathological significance of LPCAT1 and its perspective mechanism in GC tissues.

MATERIALS AND METHODS

The protein expression and mRNA levels of LPCAT1 were detected from in-house immunohistochemistry and public high-throughput RNA arrays and RNA sequencing. To have a comprehensive understanding of the clinical value of LPCAT1 in GC, all enrolled data were integrated to calculate the expression difference and standard mean difference (SMD). The biological mechanism of LPCAT1 in GC was confirmed by computational biology and in vitro experiments. Migration and invasion assays were also conducted to confirm the effect of LPCAT1 in GC.

RESULTS

Both protein and mRNA expression levels of LPCAT1 in GC were remarkably higher than those in noncancerous controls. Comprehensively, the SMD of LPCAT1 mRNA was 1.11 (95% CI = 0.86-1.36) in GC, and the summarized AUC was 0.85 based on 15 datasets containing 1727 cases of GC and 940 cases of non-GC controls. Moreover, LPCAT1 could accelerate the invasion and migration of GC by boosting the neutrophil degranulation pathway and disturbing the immune microenvironment.

CONCLUSION

An increased level of LPCAT1 may promote the progression of GC.

Abnormal chondrocyte development in a zebrafish model of cblC syndrome restored by an MMACHC cobalamin binding mutant

Variants in the MMACHC gene cause combined methylmalonic acidemia and homocystinuria cblC type, the most common inborn error of intracellular cobalamin (vitamin B12) metabolism. cblC is associated with neurodevelopmental, hematological, ocular, and biochemical abnormalities. In a subset of patients, mild craniofacial dysmorphia has also been described. Mouse models of Mmachc deletion are embryonic lethal but cause severe craniofacial phenotypes such as facial clefts. MMACHC encodes an enzyme required for cobalamin processing and variants in this gene result in the accumulation of two metabolites: methylmalonic acid (MMA) and homocysteine (HC). Interestingly, other inborn errors of cobalamin metabolism, such as cblX syndrome, are associated with mild facial phenotypes. However, the presence and severity of MMA and HC accumulation in cblX syndrome is not consistent with the presence or absence of facial phenotypes. Thus, the mechanisms by which mutations in MMACHC cause craniofacial defects are yet to be completely elucidated. Here we have characterized the craniofacial phenotypes in a zebrafish model of cblC (hg13) and performed restoration experiments with either a wildtype or a cobalamin binding deficient MMACHC protein. Homozygous mutants did not display gross morphological defects in facial development but did have abnormal chondrocyte nuclear organization and an increase in the average number of neighboring cell contacts, both phenotypes were fully penetrant. Abnormal chondrocyte nuclear organization was not associated with defects in the localization of neural crest specific markers, sox10 (RFP transgene) or barx1. Both nuclear angles and the number of neighboring cell contacts were fully restored by wildtype MMACHC and a cobalamin binding deficient variant of the MMACHC protein. Collectively, these data suggest that mutation of MMACHC causes mild to moderate craniofacial phenotypes that are independent of cobalamin binding.

A de novo YY1 missense variant expanding the Gabriele-de Vries syndrome phenotype and affecting X-chromosome inactivation

Yin and Yang 1 gene (YY1; MIM#600,013) is recognized as a dual transcriptional activating and repressing factor, RNA-binding protein, and 3D chromatin regulator, with multi roles in neurodevelopmental and maintenance pathways. YY1 haploinsufficiency caused either by heterozygous sequence variants or deletions involving the whole gene has been recently associated with Gabriele-de Vries syndrome (GADEVS), a rare congenital autosomal dominant condition, leading to intellectual disability (ID) and multiple physical/behavioural abnormalities. Herein, we describe clinical and molecular findings from a Brazilian female harbouring a de novo missense pathogenic variant in YY1 gene (NM_003403.5:c.1106A > G; p.Asn369Ser) found by whole exome sequencing with potential implications for protein structure and function. Undescribed or uncommon clinical features in this patient included non-febrile seizures, severe scoliosis, hearing impairment, and chorioretinitis. Further bioinformatics analyses using YY1-other protein interaction networks reinforced the involvement of YY1 interactors in such phenotypes, in exception of chorioretinitis. Moreover, X-chromosome inactivation (XCI) skewing was evidenced in the patient and attributed to the haploinsufficiency of YY1, which direct and indirectly interacts with numerous XCI key regulators. Besides expanding the mutational and phenotype spectrum of GADEVS, our results highlight the role of YY1 as an essential autosomal regulator of XCI epigenetic process.

Clinical characteristics and genotype analysis of five infants with cblX type of methylmalonic acidemia

OBJECTIVE

To investigate the clinical and genetic characteristics of infants with cobalamin (cbl) X type of methylmalonic acidemia (MMA).

METHODS

The clinical data of 5 infants with cblX type of MMA diagnosed in Xinhua Hospital Affiliated to Shanghai Jiao Tong University School of Medicine and Shanghai Children's Hospital from the year 2016 to 2020 were collected. The levels of blood acylcarnitines were detected by tandem mass spectrometry, the levels of urinary organic acids were detected by gas-chromatography mass spectrometry, the pathogenic genes were detected by whole exon gene sequencing, and the effect of new pathogenic mutations on three-dimensional protein structure was predicted by bioinformatics analysis.

RESULTS

Five infants with cblX type were diagnosed, including 4 males and 1 female, and the onset age was 0-6 months. The main clinical manifestations of 4 males were intractable epilepsy, mental and motor retardation, metabolic abnormalities presented mild increase of blood homocysteine level. Among them, 3 cases were accompanied by slight increase of urinary methylmalonic acid, and 1 case was accompanied by increase of blood propionylcarnitine (C3) and C3/acetylcarnitine (C2). Gene detection found that 2 cases carried a same hemizygous mutation c.344C>T (p.A115V) of HCFC1 gene, which was the most reported mutation, and the other 2 cases carried novel pathogenic mutations, c.92G>A (p.R31Q) and c.166G>C (p.V56L). These 3 gene mutations located in the Kelch domain of HCFC1 protein. One female infant carried a benign mutation of c.3731G>T (p.R1244L). Her clinical symptoms were mild, and only the urinary methylmalonic acid was slightly increased.

CONCLUSIONS

The clinical manifestations of children with cblX type of MMA are intractable epilepsy, mental and motor retardation, and other serious neurological symptoms. Their metabolic abnormalities present the increase of blood homocysteine with methylmalonic acid (urinary methylmalonic acid or/and blood C3, C3/C2). The clinical and biochemical phenotypes are separated, so the diagnosis should be in combination with the results of gene testing.

A case of methylmalonic acidemia and homocysteinemia cblX type with negative tandem mass spectrometry testing

A child with methylmalonic acidemia and homocysteinemia cblX type presented focal seizures and epileptic spasms in early infancy, but the tandem mass spectrometry tests showed negative results during neonatal screening or acute attack. Despite treated with a variety of antiepileptic drugs, the child died at age of The blood spot sample of the patient was retrospectively tested with ultrahigh performance liquid chromatography-tandem mass spectrometry, and the increased levels of methylmalonic acid and homocysteine were revealed. Whole exome sequencing showed that the proband had a c.202C>G(p.Q68E) hemizygous mutation in gene, which was inherited from his mother.