A TMEM63A Nonsense Heterozygous Variant Linked to Infantile Transient Hypomyelinating Leukodystrophy Type 19?

Infantile onset transient hypomyelination (IOTH) is a rare form of leukodystrophy that is associated with transient motor impairment and delayed central nervous system myelination. Here, we report a case of a new mutation in the transmembrane protein 63A (TMEM63A) gene identified using Whole-Exome Sequencing (WES) in an 8.5-year-old boy with clinical symptoms similar to IOTH. The patient exhibited a mild developmental delay, including hypotonia and delayed motor milestones, as well as some notable phenotypic characteristics, such as macrocephaly and macrosomia. Despite the absence of early neuroimaging, genetic testing revealed a paternally inherited variant in TMEM63A (NM_14698.3:c.220A>T;p:(Arg74*)), potentially linked to infantile transient hypomyelinating leukodystrophy type 19. Our findings in this study and the patient's favorable clinical course underscore the potential for successful myelination even with delayed initiation and may contribute to a better understanding of the genotype-phenotype correlation in IOTH, emphasizing the importance of genetic analysis in unresolved developmental delay cases and providing critical insights for accurate diagnosis, prognosis and potential therapeutic strategies in rare leukodystrophies.

Expanded phenotypic spectrum of neurodevelopmental and neurodegenerative disorder Bryant-Li-Bhoj syndrome with 38 additional individuals.

Bryant-Li-Bhoj syndrome (BLBS), which became OMIM-classified in 2022 (OMIM: 619720, 619721), is caused by germline variants in the two genes that encode histone H3.3 (H3-3A/H3F3A and H3-3B/H3F3B) [1-4]. This syndrome is characterized by developmental delay/intellectual disability, craniofacial anomalies, hyper/hypotonia, and abnormal neuroimaging [1, 5]. BLBS was initially categorized as a progressive neurodegenerative syndrome caused by de novo heterozygous variants in either H3-3A or H3-3B [1-4]. Here, we analyze the data of the 58 previously published individuals along 38 unpublished, unrelated individuals. In this larger cohort of 96 people, we identify causative missense, synonymous, and stop-loss variants. We also expand upon the phenotypic characterization by elaborating on the neurodevelopmental component of BLBS. Notably, phenotypic heterogeneity was present even amongst individuals harboring the same variant. To explore the complex phenotypic variation in this expanded cohort, the relationships between syndromic phenotypes with three variables of interest were interrogated: sex, gene containing the causative variant, and variant location in the H3.3 protein. While specific genotype-phenotype correlations have not been conclusively delineated, the results presented here suggest that the location of the variants within the H3.3 protein and the affected gene (H3-3A or H3-3B) contribute more to the severity of distinct phenotypes than sex. Since these variables do not account for all BLBS phenotypic variability, these findings suggest that additional factors may play a role in modifying the phenotypes of affected individuals. Histones are poised at the interface of genetics and epigenetics, highlighting the potential role for gene-environment interactions and the importance of future research.

The Diverse Genomic Landscape of Diamond-Blackfan Anemia: Two Novel Variants and a Mini-Review.

Diamond-Blackfan anemia (DBA) is a ribosomopathy characterized by bone marrow erythroid hypoplasia, which typically presents with severe anemia within the first months of life. DBA is typically attributed to a heterozygous mutation in a ribosomal protein (RP) gene along with a defect in the ribosomal RNA (rRNA) maturation or levels. Besides classic DBA, DBA-like disease has been described with variations in 16 genes (primarily in GATA1, followed by ADA2 alias CECR1, HEATR3, and TSR2). To date, more than a thousand variants have been reported in RP genes. Splice variants represent 6% of identifiable genetic defects in DBA, while their prevalence is 14.3% when focusing on pathogenic and likely pathogenic (P/LP) variants, thus highlighting the impact of such alterations in RP translation and, subsequently, in ribosome levels. We hereby present two cases with novel pathogenic splice variants in RPS17 and RPS26. Associations of DBA-related variants with specific phenotypic features and malignancies and the molecular consequences of pathogenic variations for each DBA-related gene are discussed. The determinants of the spontaneous remission, cancer development, variable expression of the same variants between families, and selectivity of RP defects towards the erythroid lineage remain to be elucidated.

Retrospective analysis of persistent HyperCKemia with or without muscle weakness in a case series from Greece highlights vast DMD variant heterogeneity.

BACKGROUND: Persistent hyperCKemia results from muscle dysfunction often attributed to genetic alterations of muscle-related genes, such as the dystrophin gene (DMD). Retrospective assessment of findings from DMD analysis, in association with persistent HyperCKemia, was conducted. PATIENTS AND METHODS: Evaluation of medical records from 1354 unrelated cases referred during the period 1996-2021. Assessment of data concerning the detection of DMD gene rearrangements and nucleotide variants. RESULTS: A total of 730 individuals (657 cases, 569 of Greek and 88 of Albanian origins) were identified, allowing an overall estimation of dystrophinopathy incidence at ~1:3800 live male births. The heterogeneous spectrum of 275 distinct DMD alterations comprised exon(s) deletions/duplications, nucleotide variants, and rare events, such as chromosome translocation {t(X;20)}, contiguous gene deletions, and a fused gene involving the DMD and the DOCK8 genes. Ethnic-specific findings include a common founder variant in exon 36 ('Hellenic' variant). CONCLUSIONS: Some 50% of hyperCKemia cases were characterized as dystrophinopathies, highlighting that DMD variants may be considered the most common cause of hyperCKemia in Greece. Delineation of the broad genetic and clinical heterogeneity is fundamental for actionable public health decisions and theragnosis, as well as the establishment of guidelines addressing ethical considerations, especially related to the mild asymptomatic patient subgroup.

Germline CNV Detection through Whole-Exome Sequencing (WES) Data Analysis Enhances Resolution of Rare Genetic Diseases.

Whole-Exome Sequencing (WES) has proven valuable in the characterization of underlying genetic defects in most rare diseases (RDs). Copy Number Variants (CNVs) were initially thought to escape detection. Recent technological advances enabled CNV calling from WES data with the use of accurate and highly sensitive bioinformatic tools. Amongst 920 patients referred for WES, 454 unresolved cases were further analysed using the ExomeDepth algorithm. CNVs were called, evaluated and categorized according to ACMG/ClinGen recommendations. Causative CNVs were identified in 40 patients, increasing the diagnostic yield of WES from 50.7% (466/920) to 55% (506/920). Twenty-two CNVs were available for validation and were all confirmed; of these, five were novel. Implementation of the ExomeDepth tool promoted effective identification of phenotype-relevant and/or novel CNVs. Among the advantages of calling CNVs from WES data, characterization of complex genotypes comprising both CNVs and SNVs minimizes cost and time to final diagnosis, while allowing differentiation between true or false homozygosity, as well as compound heterozygosity of variants in AR genes. The use of a specific algorithm for calling CNVs from WES data enables ancillary detection of different types of causative genetic variants, making WES a critical first-tier diagnostic test for patients with RDs.

Combined exome analysis and exome depth assessment achieve a high diagnostic yield in an epilepsy case series, revealing significant genomic heterogeneity and novel mechanisms.

OBJECTIVES: Genetics of epilepsy are highly heterogeneous and complex. Lesions detected involve genes encoding various types of channels, transcription factors, and other proteins implicated in numerous cellular processes, such as synaptogenesis. Consequently, a wide spectrum of clinical presentations and overlapping phenotypes hinders differential diagnosis and highlights the need for molecular investigations toward delineation of underlying mechanisms and final diagnosis. Characterization of defects may also contribute valuable data on genetic landscapes and networks implicated in epileptogenesis. METHODS: This study reports on genetic findings from exome sequencing (ES) data of 107 patients with variable types of seizures, with or without additional symptoms, in the context of neurodevelopmental disorders. RESULTS: Multidisciplinary evaluation of ES, including ancillary detection of copy number variants (CNVs) with the ExomeDepth tool, supported a definite diagnosis in 59.8% of the patients, reflecting one of the highest diagnostic yields in epilepsy. CONCLUSION: Emerging advances of next-generation technologies and 'in silico' analysis tools offer the possibility to simultaneously detect several types of variations. Wide assessment of variable findings, specifically those found to be novel and least expected, reflects the ever-evolving genetic landscape of seizure development, potentially beneficial for increased opportunities for trial recruitment and enrollment, and optimized, even personalized, medical management.

CAPRIN1 haploinsufficiency causes a neurodevelopmental disorder with language impairment, ADHD and ASD.

We describe an autosomal dominant disorder associated with loss-of-function variants in the Cell cycle associated protein 1 (CAPRIN1; MIM*601178). CAPRIN1 encodes a ubiquitous protein that regulates the transport and translation of neuronal mRNAs critical for synaptic plasticity, as well as mRNAs encoding proteins important for cell proliferation and migration in multiple cell types. We identified 12 cases with loss-of-function CAPRIN1 variants, and a neurodevelopmental phenotype characterized by language impairment/speech delay (100%), intellectual disability (83%), attention deficit hyperactivity disorder (82%) and autism spectrum disorder (67%). Affected individuals also had respiratory problems (50%), limb/skeletal anomalies (50%), developmental delay (42%) feeding difficulties (33%), seizures (33%) and ophthalmologic problems (33%). In patient-derived lymphoblasts and fibroblasts, we showed a monoallelic expression of the wild-type allele, and a reduction of the transcript and protein compatible with a half dose. To further study pathogenic mechanisms, we generated sCAPRIN1+/- human induced pluripotent stem cells via CRISPR-Cas9 mutagenesis and differentiated them into neuronal progenitor cells and cortical neurons. CAPRIN1 loss caused reduced neuronal processes, overall disruption of the neuronal organization and an increased neuronal degeneration. We also observed an alteration of mRNA translation in CAPRIN1+/- neurons, compatible with its suggested function as translational inhibitor. CAPRIN1+/- neurons also showed an impaired calcium signalling and increased oxidative stress, two mechanisms that may directly affect neuronal networks development, maintenance and function. According to what was previously observed in the mouse model, measurements of activity in CAPRIN1+/- neurons via micro-electrode arrays indicated lower spike rates and bursts, with an overall reduced activity. In conclusion, we demonstrate that CAPRIN1 haploinsufficiency causes a novel autosomal dominant neurodevelopmental disorder and identify morphological and functional alterations associated with this disorder in human neuronal models.

A novel pathogenic ATP6V1B2 variant: Widening the genotypic spectrum of the epileptic neurodevelopmental phenotype.

ATP6V1B2 pathogenic variants are linked with variable phenotypes, such as dominant deafness-onychodystrophy syndrome (DDOD), autosomal dominant Zimmermann-Laband syndrome type 2 (ZLS2), and some cases of DOORS (deafness, onychodystrophy, osteodystrophy, intellectual disability [ID], and seizures). Epilepsy was first linked to ATP6V1B2, when the p.(Glu374Gln) missense variant was detected in a patient with ID and seizures, but without characteristic features of DDOD or ZLS2 syndromes. We herein report a novel pathogenic ATP6V1B2:p.Glu374Gly variant detected in an adult patient with ID and myoclonic-atonic seizures. The (re)occurrence of different variants affecting the same highly conserved hydrophilic glutamic acid on position 374 of the V-proton ATPase subunit B, indicates a potential novel pathogenic hotspot and a critical role for the specific residue in the development of epilepsy. ATP6V1B2 gene defects should be considered when analyzing patients with epilepsy, even in the absence of most cardinal features of DDOD, DOORS, or ZLS such as deafness, onychodystrophy, and osteodystrophy.

Ovarian insufficiency and secondary amenorrhea in a patient with a novel variant within GDF9 gene.

OBJECTIVE: Premature ovarian insufficiency is a heterogeneous condition that can be caused by several factors, such as genetic, environmental, etc. and represents one of the main causes of female infertility. One of the genes implicated is GDF9, which encodes a member of the transforming growth factor-beta superfamily that participates in the coordination of somatic cell activity, female fertility, including folliculogenesis, and oocyte maturation. Damaging variants in GDF9-encoded growth factors can cause the production of inhibin, perturb oocyte granulosa cell microenvironments, and obstruct follicle development. A novel GDF9 variant is herein reported to consolidate the role of GDF9 in ovarian function and female fertility. METHODS: A 38-year-old female was referred for the investigation of secondary amenorrhea. Eventually, she was referred for genetic evaluation whereby conventional karyotyping and Fragile-X molecular testing were normal. Whole Exome Sequencing was performed, followed by targeted Sanger sequencing in all family members for variant confirmation and evaluation. RESULTS: In this study we report a patient presenting with secondary amenorrhea due to premature ovarian failure and a pituitary lesion with radiological characteristics compatible with a Rathke cyst or a macroadenoma, residing between the adenohypophysis and neurohypophysis. Whole Exome Sequencing revealed a novel heterozygous stoploss variant c.1364A>C, p.(*455Serext*8) in the GDF9 gene. CONCLUSIONS: Should the predicted elongated GDF9 protein and differentially configurated GDF9 mature protein molecule form unstable dimers, rapid proteolytic degradation may take place and inhibit homo/heterodimer formation.

Phenotype-driven variant filtration strategy in exome sequencing toward a high diagnostic yield and identification of 85 novel variants in 400 patients with rare Mendelian disorders.

About 6000 to 7000 different rare disorders with suspected genetic etiologies have been described and almost 4500 causative gene(s) have been identified. The advent of next-generation sequencing (NGS) technologies has revolutionized genomic research and diagnostics, representing a major advance in the identification of pathogenic genetic variations. This study presents a 3-year experience from an academic genetics center, where 400 patients were referred for genetic analysis of disorders with unknown etiology. A phenotype-driven proband-only exome sequencing (ES) strategy was applied for the investigation of rare disorders, in the context of optimizing ES diagnostic yield and minimizing costs and time to definitive diagnosis. Overall molecular diagnostic yield reached 53% and characterized 243 pathogenic variants in 210 cases, 85 of which were novel and 148 known, contributing information to the community of disease and variant databases. ES provides an opportunity to resolve the genetic etiology of disorders and support appropriate medical management and genetic counseling. In cases with complex phenotypes, the identification of complex genotypes may contribute to more comprehensive clinical management. In the context of effective multidisciplinary collaboration between clinicians and laboratories, ES provides an efficient and appropriate tool for first-tier genomic analysis.

Detection of a novel unbalanced X;21 translocation in a girl with Turner syndrome phenotype.

OBJECTIVE: To describe a novel unbalanced X;21 translocation resulting in a derivative pseudodicentric chromosome X;21 lacking the critical region for ovarian development and function, in a 16-year-old girl referred for cytogenetic analysis due to primary amenorrhea and Turner-like features. METHODS: Cytogenetic analysis of the proband and her parents was performed on peripheral blood lymphocytes by GTG banding. Molecular cytogenetic FISH analysis was performed on metaphase preparations, using X chromosome centromeric probe and telomeric and pancentromeric peptide nucleic acid (PNA) analog probes. The HUMARA assay as well as methylation studies for PCSK1N and FMR-1 loci were performed. RESULTS: Cytogenetic analysis revealed a de novo unbalanced X;21 translocation, described as 45,X,der(X)t(X;21)(q22.2;p11.2),-21. FISH analysis showed that the derivative X chromosome carried both the X and 21 centromeres, as well as, the Xp and 21q telomeres. The karyotype was thus reevaluated as 45,X,psu dic(21;X)(21qter→21p13::Xq22.2→Xpter),-21. X inactivation studies revealed that the derivative chromosome was of paternal origin and confirmed the selective inactivation of the derivative X segment of the pseudodicentric chromosome. CONCLUSIONS: Primary amenorrhea and other Turner-like characteristics of the proband are apparently due to the loss of the Xq22.2→Xqter critical region which contains critical genes for the ovarian development and function. The chromosome X segment of the derivative pseudodicentric chromosome is selectively inactivated, but inactivation does not seem to spread onto the translocated chromosome 21, accounting probably for the lack of severe clinical consequences which would result from monosomy 21.