De novo missense variants in phosphatidylinositol kinase PIP5KIγ underlie a neurodevelopmental syndrome associated with altered phosphoinositide signaling.

Phosphoinositides (PIs) are membrane phospholipids produced through the local activity of PI kinases and phosphatases that selectively add or remove phosphate groups from the inositol head group. PIs control membrane composition and play key roles in many cellular processes including actin dynamics, endosomal trafficking, autophagy, and nuclear functions. Mutations in phosphatidylinositol 4,5 bisphosphate [PI(4,5)P2] phosphatases cause a broad spectrum of neurodevelopmental disorders such as Lowe and Joubert syndromes and congenital muscular dystrophy with cataracts and intellectual disability, which are thus associated with increased levels of PI(4,5)P2. Here, we describe a neurodevelopmental disorder associated with an increase in the production of PI(4,5)P2 and with PI-signaling dysfunction. We identified three de novo heterozygous missense variants in PIP5K1C, which encodes an isoform of the phosphatidylinositol 4-phosphate 5-kinase (PIP5KIγ), in nine unrelated children exhibiting intellectual disability, developmental delay, acquired microcephaly, seizures, visual abnormalities, and dysmorphic features. We provide evidence that the PIP5K1C variants result in an increase of the endosomal PI(4,5)P2 pool, giving rise to ectopic recruitment of filamentous actin at early endosomes (EEs) that in turn causes dysfunction in EE trafficking. In addition, we generated an in vivo zebrafish model that recapitulates the disorder we describe with developmental defects affecting the forebrain, including the eyes, as well as craniofacial abnormalities, further demonstrating the pathogenic effect of the PIP5K1C variants.

Riboflavin transporter deficiency mimicking mitochondrial myopathy caused by complex II deficiency.

Biallelic likely pathogenic variants in SLC52A2 and SLC52A3 cause riboflavin transporter deficiency. It is characterized by muscle weakness, ataxia, progressive ponto-bulbar palsy, amyotrophy, and sensorineural hearing loss. Oral riboflavin halts disease progression and may reverse symptoms. We report two new patients whose clinical and biochemical features were mimicking mitochondrial myopathy. Patient 1 is an 8-year-old male with global developmental delay, axial and appendicular hypotonia, ataxia, and sensorineural hearing loss. His muscle biopsy showed complex II deficiency and ragged red fibers consistent with mitochondrial myopathy. Whole exome sequencing revealed a homozygous likely pathogenic variant in SLC52A2 (c.917G>A; p.Gly306Glu). Patient 2 is a 14-month-old boy with global developmental delay, respiratory insufficiency requiring ventilator support within the first year of life. His muscle biopsy revealed combined complex II + III deficiency and ragged red fibers consistent with mitochondrial myopathy. Whole exome sequencing identified a homozygous likely pathogenic variant in SCL52A3 (c.1223G>A; p.Gly408Asp). We report two new patients with riboflavin transporter deficiency, caused by mutations in two different riboflavin transporter genes. Both patients presented with complex II deficiency. This treatable neurometabolic disorder can mimic mitochondrial myopathy. In patients with complex II deficiency, riboflavin transporter deficiency should be included in the differential diagnosis to allow early treatment and improve neurodevelopmental outcome.

Primary mediastinal paraganglioma associated with a familial variant in the succinate dehydrogenase B subunit gene.

Surgical management is the mainstay of therapy for primary cardiac tumors, yet due to the rarity of these malignancies, their management and workup remains a challenge. Here, we report a unique case of a patient with a primary left ventricular cardiac paraganglioma (PGL) and describe the role of a medical genetics assessment leading to the identification of a rare variant in the SDHB gene to be the causative etiology of this cardiac tumor. Due to decreasing costs and accessibility of molecular genetic analysis, genetic testing may become an emerging diagnostic adjunct in cases of cardiac tumors.

De novo pathogenic variant in TUBB2A presenting with arthrogryposis multiplex congenita, brain abnormalities, and severe developmental delay.

Disorders of brain formation can occur from pathogenic variants in various alpha and beta tubulin genes. Heterozygous pathogenic variants in the beta tubulin isotype A gene, TUBB2A, have been recently implicated in brain malformations, seizures, and developmental delay. Limited information is known regarding the phenotypic spectrum associated with pathogenic variants in this gene given the rarity of the condition. We report the sixth individual with a de novo heterozygous TUBB2A pathogenic variant, who presented with a severe neurological phenotype along with unique features of arthrogryposis multiplex congenita, optic nerve hypoplasia, dysmorphic facial features, and vocal cord paralysis, thereby expanding the gene-related phenotype.

Lateral meningocele (Lehman) syndrome: A child with a novel NOTCH3 mutation.

Lateral meningocele syndrome (LMS), or Lehman syndrome, is a rare disorder characterized by multiple lateral spinal meningoceles, distinctive facial features, joint hypermobility and hypotonia, along with skeletal, cardiac, and urogenital anomalies. Heterozygous NOTCH3 mutations affecting the terminal exon 33 were recently reported as causative in six families with LMS. We report a boy with LMS, the fourteenth reported case, with a de novo 80 base pair deletion in exon 33 of NOTCH3. Our patient's prenatal findings, complex cardiac anomalies, and severe feeding difficulties further expand our understanding of this rare condition.

The Genetics of Tuberous Sclerosis Complex and Related mTORopathies: Current Understanding and Future Directions.

The mechanistic target of rapamycin (mTOR) pathway serves as a master regulator of cell growth, proliferation, and survival. Upregulation of the mTOR pathway has been shown to cause malformations of cortical development, medically refractory epilepsies, and neurodevelopmental disorders, collectively described as mTORopathies. Tuberous sclerosis complex (TSC) serves as the prototypical mTORopathy. Characterized by the development of benign tumors in multiple organs, pathogenic variants in TSC1 or TSC2 disrupt the TSC protein complex, a negative regulator of the mTOR pathway. Variants in critical domains of the TSC complex, especially in the catalytic TSC2 subunit, correlate with increased disease severity. Variants in less crucial exons and non-coding regions, as well as those undetectable with conventional testing, may lead to milder phenotypes. Despite the assumption of complete penetrance, expressivity varies within families, and certain variants delay disease onset with milder neurological effects. Understanding these genotype-phenotype correlations is crucial for effective clinical management. Notably, 15% of patients have no mutation identified by conventional genetic testing, with the majority of cases postulated to be caused by somatic TSC1/TSC2 variants which present complex diagnostic challenges. Advancements in genetic testing, prenatal screening, and precision medicine hold promise for changing the diagnostic and treatment paradigm for TSC and related mTORopathies. Herein, we explore the genetic and molecular mechanisms of TSC and other mTORopathies, emphasizing contemporary genetic methods in understanding and diagnosing the condition.

Diagnosis and clinical presentation of two individuals with a rare TCF20 pathogenic variant.

TCF20-associated neurodevelopmental disorder (TAND) is a rare and phenotypically variable genetic condition. Common features include intellectual disability, neurobehavioural concerns, postnatal tall stature and hypotonia.Two unrelated early adolescent males were referred to genetics for assessment of developmental delay. The first male of Caucasian descent had a history of autism spectrum disorder (ASD), mitral valve prolapse and subtle craniofacial dysmorphisms. The second male of Somali descent had a history of intellectual disability, thick corpus callosum and ASD. Whole-exome sequencing revealed a pathogenic variant in TCF20 in both individuals. Further testing revealed that the former individual's mother was mosaic for the TCF20 pathogenic variant.We report two individuals with TCF20 pathogenic variants presenting with unique findings, including thick corpus callosum, family history of mosaicism and cardiac anomalies. These examples expand the TAND phenotype, describe associated dysmorphism in a minority group and highlight the importance of rare disease research.

Pathogenic DNM1 Gene Variant Presenting With Unusually Nonsevere Neurodevelopmental Phenotype: A Case Report.

BACKGROUND AND OBJECTIVES: To date, all reports of pathogenic variants affecting the GTPase domain of the DNM1 gene have a clinically severe neurodevelopmental phenotype, including severe delays or intractable epilepsy. We describe a case with moderate developmental delays and self-resolved epilepsy. METHODS: The patient was followed by our neurology and genetics teams. After clinical examination and EEG to characterize the patient's presentation, we conducted etiologic workup including brain MRI, chromosomal microarray, genetic and metabolic investigations, and nerve conduction studies. Subsequently, we arranged an Intellectual Disability Plus Trio Panel. RESULTS: Our patient presented with seizures at 2 days old, requiring phenobarbital. She also had hypotonia, mild dysmorphic features, and mild ataxia. Although initial workup returned unremarkable, the trio gene panel identified a de novo heterozygous pathogenic missense variant in the DNM1 GTPase domain. Now 4 years old, she has been seizure-free for 3 years without ongoing treatment and has nonsevere developmental delays (e.g., ambulates independently and speaks 2-word phrases). DISCUSSION: Our case confirms that not all individuals with DNM1 pathogenic variants, even affecting the GTPase domain, will present with intractable epilepsy or severe delays. Expanding the known clinical spectrum of dynamin-related neurodevelopmental disorder is crucial for patient prognostication and counseling.

Management of major bleeds in patients with immune thrombocytopenia.

BACKGROUND: A standard approach to the recognition and management of major bleeding in immune thrombocytopenia (ITP) is lacking. METHODS: Retrospective cohort study of ITP patients presenting to the emergency department (ED) with severe thrombocytopenia (platelet count <20 × 109 /L) and bleeding in four academic hospitals from 2008 to 2016. We defined a major ITP bleed as a bleed at a critical site or causing hemodynamic instability. RESULTS: We identified 112 ITP patients (n = 141 visits) who presented to the ED with platelets <20 × 109 /L and bleeding. Twenty--nine patients (26%) had 32 ED visits with major bleeds. Risk factors for major bleeds were older age (odds ratio [OR] 1.03, 95% confidence interval [CI] 1.01-1.06), male sex (OR 3.25, 95% CI 1.22-9.32), and more prior ITP therapies (OR 1.42, 95% CI 1.10-1.87). Acute treatment of major bleeds required a median of three treatments (interquartile range [IQR] 2--4), which included intravenous immune globulin (91% of visits), corticosteroids (78% of visits), and platelet transfusions (75% of visits). Three patients (10%) died, nine (31%) developed recurrent bleeds, one (3%) developed arterial thrombosis, and one (3%) had permanent neurological disability. Six patients presented with minor bleeding and subsequently developed a major bleed after a median of 2 days (IQR 1-3). All six patients had oral purpura and four of six had gross hematuria preceding the major bleed. CONCLUSIONS: Major ITP bleeds are associated with significant morbidity and mortality. Oral purpura and hematuria often preceded major bleeds. Further research is needed to refine the definition of a major ITP bleed and develop evidence-based treatment strategies.

New insights into DNA methylation signatures: SMARCA2 variants in Nicolaides-Baraitser syndrome.

BACKGROUND: Nicolaides-Baraitser syndrome (NCBRS) is a neurodevelopmental disorder caused by pathogenic sequence variants in SMARCA2 which encodes the catalytic component of the chromatin remodeling BAF complex. Pathogenic variants in genes that encode epigenetic regulators have been associated with genome-wide changes in DNA methylation (DNAm) in affected individuals termed DNAm signatures. METHODS: Genome-wide DNAm was assessed in whole-blood samples from the individuals with pathogenic SMARCA2 variants and NCBRS diagnosis (n = 8) compared to neurotypical controls (n = 23) using the Illumina MethylationEPIC array. Differential methylated CpGs between groups (DNAm signature) were identified and used to generate a model enabling classification variants of uncertain significance (VUS; n = 9) in SMARCA2 as "pathogenic" or "benign". A validation cohort of NCBRS cases (n = 8) and controls (n = 96) demonstrated 100% model sensitivity and specificity. RESULTS: We identified a DNAm signature of 429 differentially methylated CpG sites in individuals with NCBRS. The genes to which these CpG sites map are involved in cell differentiation, calcium signaling, and neuronal function consistent with NCBRS pathophysiology. DNAm model classifications of VUS were concordant with the clinical phenotype; those within the SMARCA2 ATPase/helicase domain classified as "pathogenic". A patient with a mild neurodevelopmental NCBRS phenotype and a VUS distal to the ATPase/helicase domain did not score as pathogenic, clustering away from cases and controls. She demonstrated an intermediate DNAm profile consisting of one subset of signature CpGs with methylation levels characteristic of controls and another characteristic of NCBRS cases; each mapped to genes with ontologies consistent with the patient's unique clinical presentation. CONCLUSIONS: Here we find that a DNAm signature of SMARCA2 pathogenic variants in NCBRS maps to CpGs relevant to disorder pathophysiology, classifies VUS, and is sensitive to the position of the variant in SMARCA2. The patient with an intermediate model score demonstrating a unique genotype-epigenotype-phenotype correlation underscores the potential utility of this signature as a functionally relevant VUS classification system scalable beyond binary "benign" versus "pathogenic" scoring. This is a novel feature of DNAm signatures that could enable phenotypic predictions from genotype data. Our findings also demonstrate that DNAm signatures can be domain-specific, highlighting the precision with which they can reflect genotypic variation.

Stable transmission of an unbalanced chromosome 21 derived from chromoanasynthesis in a patient with a SYNGAP1 likely pathogenic variant.

BACKGROUND: Complex genomic structural variations, involving chromoanagenesis, have been implicated in multiple congenital anomalies and abnormal neurodevelopment. Familial inheritance of complex chromosomal structural alteration resulting from germline chromoanagenesis-type mechanisms are limited. CASE PRESENTATION: We report a two-year eleven-month old male presenting with epilepsy, ataxia and dysmorphic features of unknown etiology. Chromosomal microarray identified a complex unbalanced rearrangement involving chromosome 21. G-banding and FISH for targeted regions of chromosome 21 revealed that the copy number imbalances were limited to gains dispersed throughout the long arm of chromosome 21, characteristic of a chromosome derived from chromoanagenesis. Family studies showed that the unbalanced chromosome had been stably inherited, as it was present in both his healthy mother and maternal grandfather. Further molecular testing for non-syndromic intellectual disability genes found a likely pathogenic mutation in SYNGAP1 (NM_006772.2:c.3722_3723del). CONCLUSIONS: This study indicates that complex rearrangements involving an unbalanced chromosome derived from chromoanasynthesis can be familial and should be not be presumed pathogenic.

Impact of Mobility Device Use on Quality of Life in Children With Friedreich Ataxia.

OBJECTIVE: To determine how mobility device use impacts quality of life in children with Friedreich ataxia. STUDY DESIGN: Data from 111 pediatric patients with genetically confirmed Friedreich ataxia were collected from a prospective natural history study utilizing standardized clinical evaluations, including health-related quality of life using the Pediatric Quality of Life Inventory (PedsQL) 4.0 Generic Core Module. RESULTS: Mobility device use was associated with worse mean PedsQL total, physical, emotional, social, and academic subscores, after adjusting for gender, age of disease onset, and Friedreich Ataxia Rating Scale score. The magnitude of the difference was greatest for the physical subscore (-19.5 points, 95% CI = -30.00, -8.99, P < .001) and least for the emotional subscore (-10.61 points, 95% CI = -20.21, -1.02, P = .03). Transition to or between mobility devices trended toward worse physical subscore (-16.20 points, 95% CI = -32.07, -0.33, P = .05). CONCLUSIONS: Mobility device use is associated with significant worsening of all domains of quality of life in children with Friedreich ataxia.

The evolving features of Nicolaides-Baraitser syndrome - a clinical report of a 20-year follow-up.

Nicolaides-Baraitser syndrome (NCBRS) is a rare genetic condition associated with SMARCA2 gene mutations. Clinical diagnosis is challenging as its features evolve with time. The 20 years follow-up of our NCBRS patient, with a previously unreported SMARCA2 mutation, illustrates the syndrome's natural history and its clinical variability, especially in a milder form.

Child Neurology: Diencephalic syndrome-like presentation of a cervicomedullary brainstem tumor.

Diencephalic syndrome is a rare clinical entity, traditionally encompassing severe failure to thrive, nystagmus, and hyperkinesis, secondary to an intracranial neoplasm that is classically located in the hypothalamic region and its vicinity. However, the presenting features can be variable, often resulting in delayed diagnosis, which may worsen prognosis. This case report describes the atypical presentation of a posterior fossa tumor with features reminiscent of diencephalic syndrome that have not previously been reported in the literature. We report a 21-month-old girl with a cervicomedullary brainstem astrocytoma, who presented with isolated gross motor developmental delay, decreased growth velocity, and stridor. The neurologic signs frequently reported in patients with diencephalic syndrome were absent; however, severe failure to thrive was present. This case broadens the etiologic differential diagnosis of diencephalic syndrome in addition to the traditional hypothalamic region tumor location. This case urges physicians to consider central neurologic processes in the differential diagnosis of children with refractory failure to thrive with or without classical features of diencephalic syndrome, in whom etiology is not identified by routine investigations, given its importance in determining prognosis and management.

Whole Genome Sequencing Expands Diagnostic Utility and Improves Clinical Management in Pediatric Medicine.

The standard of care for first-tier clinical investigation of the etiology of congenital malformations and neurodevelopmental disorders is chromosome microarray analysis (CMA) for copy number variations (CNVs), often followed by gene(s)-specific sequencing searching for smaller insertion-deletions (indels) and single nucleotide variant (SNV) mutations. Whole genome sequencing (WGS) has the potential to capture all classes of genetic variation in one experiment; however, the diagnostic yield for mutation detection of WGS compared to CMA, and other tests, needs to be established. In a prospective study we utilized WGS and comprehensive medical annotation to assess 100 patients referred to a paediatric genetics service and compared the diagnostic yield versus standard genetic testing. WGS identified genetic variants meeting clinical diagnostic criteria in 34% of cases, representing a 4-fold increase in diagnostic rate over CMA (8%) (p-value = 1.42e-05) alone and >2-fold increase in CMA plus targeted gene sequencing (13%) (p-value = 0.0009). WGS identified all rare clinically significant CNVs that were detected by CMA. In 26 patients, WGS revealed indel and missense mutations presenting in a dominant (63%) or a recessive (37%) manner. We found four subjects with mutations in at least two genes associated with distinct genetic disorders, including two cases harboring a pathogenic CNV and SNV. When considering medically actionable secondary findings in addition to primary WGS findings, 38% of patients would benefit from genetic counseling. Clinical implementation of WGS as a primary test will provide a higher diagnostic yield than conventional genetic testing and potentially reduce the time required to reach a genetic diagnosis.