Bi-allelic variants in neuronal cell adhesion molecule cause a neurodevelopmental disorder characterized by developmental delay, hypotonia, neuropathy/spasticity.

Cell adhesion molecules are membrane-bound proteins predominantly expressed in the central nervous system along principal axonal pathways with key roles in nervous system development, neural cell differentiation and migration, axonal growth and guidance, myelination, and synapse formation. Here, we describe ten affected individuals with bi-allelic variants in the neuronal cell adhesion molecule NRCAM that lead to a neurodevelopmental syndrome of varying severity; the individuals are from eight families. This syndrome is characterized by developmental delay/intellectual disability, hypotonia, peripheral neuropathy, and/or spasticity. Computational analyses of NRCAM variants, many of which cluster in the third fibronectin type III (Fn-III) domain, strongly suggest a deleterious effect on NRCAM structure and function, including possible disruption of its interactions with other proteins. These findings are corroborated by previous in vitro studies of murine Nrcam-deficient cells, revealing abnormal neurite outgrowth, synaptogenesis, and formation of nodes of Ranvier on myelinated axons. Our studies on zebrafish nrcamaΔ mutants lacking the third Fn-III domain revealed that mutant larvae displayed significantly altered swimming behavior compared to wild-type larvae (p < 0.03). Moreover, nrcamaΔ mutants displayed a trend toward increased amounts of α-tubulin fibers in the dorsal telencephalon, demonstrating an alteration in white matter tracts and projections. Taken together, our study provides evidence that NRCAM disruption causes a variable form of a neurodevelopmental disorder and broadens the knowledge on the growing role of the cell adhesion molecule family in the nervous system.

TNPO2 variants associate with human developmental delays, neurologic deficits, and dysmorphic features and alter TNPO2 activity in Drosophila.

Transportin-2 (TNPO2) mediates multiple pathways including non-classical nucleocytoplasmic shuttling of >60 cargoes, such as developmental and neuronal proteins. We identified 15 individuals carrying de novo coding variants in TNPO2 who presented with global developmental delay (GDD), dysmorphic features, ophthalmologic abnormalities, and neurological features. To assess the nature of these variants, functional studies were performed in Drosophila. We found that fly dTnpo (orthologous to TNPO2) is expressed in a subset of neurons. dTnpo is critical for neuronal maintenance and function as downregulating dTnpo in mature neurons using RNAi disrupts neuronal activity and survival. Altering the activity and expression of dTnpo using mutant alleles or RNAi causes developmental defects, including eye and wing deformities and lethality. These effects are dosage dependent as more severe phenotypes are associated with stronger dTnpo loss. Interestingly, similar phenotypes are observed with dTnpo upregulation and ectopic expression of TNPO2, showing that loss and gain of Transportin activity causes developmental defects. Further, proband-associated variants can cause more or less severe developmental abnormalities compared to wild-type TNPO2 when ectopically expressed. The impact of the variants tested seems to correlate with their position within the protein. Specifically, those that fall within the RAN binding domain cause more severe toxicity and those in the acidic loop are less toxic. Variants within the cargo binding domain show tissue-dependent effects. In summary, dTnpo is an essential gene in flies during development and in neurons. Further, proband-associated de novo variants within TNPO2 disrupt the function of the encoded protein. Hence, TNPO2 variants are causative for neurodevelopmental abnormalities.

De novo TRIM8 variants impair its protein localization to nuclear bodies and cause developmental delay, epilepsy, and focal segmental glomerulosclerosis.

Focal segmental glomerulosclerosis (FSGS) is the main pathology underlying steroid-resistant nephrotic syndrome (SRNS) and a leading cause of chronic kidney disease. Monogenic forms of pediatric SRNS are predominantly caused by recessive mutations, while the contribution of de novo variants (DNVs) to this trait is poorly understood. Using exome sequencing (ES) in a proband with FSGS/SRNS, developmental delay, and epilepsy, we discovered a nonsense DNV in TRIM8, which encodes the E3 ubiquitin ligase tripartite motif containing 8. To establish whether TRIM8 variants represent a cause of FSGS, we aggregated exome/genome-sequencing data for 2,501 pediatric FSGS/SRNS-affected individuals and 48,556 control subjects, detecting eight heterozygous TRIM8 truncating variants in affected subjects but none in control subjects (p = 3.28 × 10-11). In all six cases with available parental DNA, we demonstrated de novo inheritance (p = 2.21 × 10-15). Reverse phenotyping revealed neurodevelopmental disease in all eight families. We next analyzed ES from 9,067 individuals with epilepsy, yielding three additional families with truncating TRIM8 variants. Clinical review revealed FSGS in all. All TRIM8 variants cause protein truncation clustering within the last exon between residues 390 and 487 of the 551 amino acid protein, indicating a correlation between this syndrome and loss of the TRIM8 C-terminal region. Wild-type TRIM8 overexpressed in immortalized human podocytes and neuronal cells localized to nuclear bodies, while constructs harboring patient-specific variants mislocalized diffusely to the nucleoplasm. Co-localization studies demonstrated that Gemini and Cajal bodies frequently abut a TRIM8 nuclear body. Truncating TRIM8 DNVs cause a neuro-renal syndrome via aberrant TRIM8 localization, implicating nuclear bodies in FSGS and developmental brain disease.

Two years of newborn screening for Duchenne muscular dystrophy as a part of the statewide Early Check research program in North Carolina.

PURPOSE: Current and emerging treatments for Duchenne muscular dystrophy (DMD) position DMD as a candidate condition for newborn screening (NBS). In anticipation of the nomination of DMD for universal NBS, we conducted a prospective study under the Early Check voluntary NBS research program in North Carolina, United States. METHODS: We performed screening for creatine kinase-MM (CK-MM), a biomarker of muscle damage, on residual routine newborn dried blood spots (DBS) from participating newborns. Total creatine kinase testing and next generation sequencing of an 86-neuromuscular gene panel that included DMD were offered to parents of newborns who screened positive. Bivariate and multivariable analyses were performed to assess effects of biological and demographic predictors on CK-MM levels in DBS. RESULTS: We screened 13,354 newborns and identified 2 males with DMD. The provisional 1626 ng/mL cutoff was raised to 2032 ng/mL to improve specificity, and additional cutoffs (900 and 360 ng/mL) were implemented to improve sensitivity for older and low-birthweight newborns. CONCLUSION: Population-scale screening for elevated CK-MM in DBS is a feasible approach to identify newborns with DMD. Inclusion of birthweight- and age-specific cutoffs, repeat creatine kinase testing after 72 hours of age, and DMD sequencing improve sensitivity and specificity of screening.

SPTSSA variants alter sphingolipid synthesis and cause a complex hereditary spastic paraplegia.

Sphingolipids are a diverse family of lipids with critical structural and signalling functions in the mammalian nervous system, where they are abundant in myelin membranes. Serine palmitoyltransferase, the enzyme that catalyses the rate-limiting reaction of sphingolipid synthesis, is composed of multiple subunits including an activating subunit, SPTSSA. Sphingolipids are both essential and cytotoxic and their synthesis must therefore be tightly regulated. Key to the homeostatic regulation are the ORMDL proteins that are bound to serine palmitoyltransferase and mediate feedback inhibition of enzymatic activity when sphingolipid levels become excessive. Exome sequencing identified potential disease-causing variants in SPTSSA in three children presenting with a complex form of hereditary spastic paraplegia. The effect of these variants on the catalytic activity and homeostatic regulation of serine palmitoyltransferase was investigated in human embryonic kidney cells, patient fibroblasts and Drosophila. Our results showed that two different pathogenic variants in SPTSSA caused a hereditary spastic paraplegia resulting in progressive motor disturbance with variable sensorineural hearing loss and language/cognitive dysfunction in three individuals. The variants in SPTSSA impaired the negative regulation of serine palmitoyltransferase by ORMDLs leading to excessive sphingolipid synthesis based on biochemical studies and in vivo studies in Drosophila. These findings support the pathogenicity of the SPTSSA variants and point to excessive sphingolipid synthesis due to impaired homeostatic regulation of serine palmitoyltransferase as responsible for defects in early brain development and function.

A concurrent dual analysis of genomic data augments diagnoses: Experiences of 2 clinical sites in the Undiagnosed Diseases Network.

PURPOSE: Next-generation sequencing (NGS) has revolutionized the diagnostic process for rare/ultrarare conditions. However, diagnosis rates differ between analytical pipelines. In the National Institutes of Health-Undiagnosed Diseases Network (UDN) study, each individual's NGS data are concurrently analyzed by the UDN sequencing core laboratory and the clinical sites. We examined the outcomes of this practice. METHODS: A retrospective review was performed at 2 UDN clinical sites to compare the variants and diagnoses/candidate genes identified with the dual analyses of the NGS data. RESULTS: In total, 95 individuals had 100 diagnoses/candidate genes. There was 59% concordance between the UDN sequencing core laboratories and the clinical sites in identifying diagnoses/candidate genes. The core laboratory provided more diagnoses, whereas the clinical sites prioritized more research variants/candidate genes (P < .001). The clinical sites solely identified 15% of the diagnoses/candidate genes. The differences between the 2 pipelines were more often because of variant prioritization disparities than variant detection. CONCLUSION: The unique dual analysis of NGS data in the UDN synergistically enhances outcomes. The core laboratory provided a clinical analysis with more diagnoses and the clinical sites prioritized more research variants/candidate genes. Implementing such concurrent dual analyses in other genomic research studies and clinical settings can improve both variant detection and prioritization.

Biallelic variants in ribonuclease inhibitor (RNH1), an inflammasome modulator, are associated with a distinctive subtype of acute, necrotizing encephalopathy.

PURPOSE: Mendelian etiologies for acute encephalopathies in previously healthy children are poorly understood, with the exception of RAN binding protein 2 (RANBP2)-associated acute necrotizing encephalopathy subtype 1 (ANE1). We provide clinical, genetic, and neuroradiological evidence that biallelic variants in ribonuclease inhibitor (RNH1) confer susceptibility to a distinctive ANE subtype. METHODS: This study aimed to evaluate clinical data, neuroradiological studies, genomic sequencing, and protein immunoblotting results in 8 children from 4 families who experienced acute febrile encephalopathy. RESULTS: All 8 healthy children became acutely encephalopathic during a viral/febrile illness and received a variety of immune modulation treatments. Long-term outcomes varied from death to severe neurologic deficits to normal outcomes. The neuroradiological findings overlapped with ANE but had distinguishing features. All affected children had biallelic predicted damaging variants in RNH1: a subset that was studied had undetectable RNH1 protein. Incomplete penetrance of the RNH1 variants was evident in 1 family. CONCLUSION: Biallelic variants in RNH1 confer susceptibility to a subtype of ANE (ANE2) in previously healthy children. Intensive immunological treatments may alter outcomes. Genomic sequencing in children with unexplained acute febrile encephalopathy can detect underlying genetic etiologies, such as RNH1, and improve outcomes in the probands and at-risk siblings.

Use of a web-based portal to return normal individual research results in Early Check: Exploring user behaviors and attitudes.

Early Check is a voluntary, large-scale expanded newborn screening study in North Carolina that uses a self-directed web-based portal for return of normal individual research results (IRR). Little is known about participant perspectives in using web-based portals to receive IRR. This study explored user attitudes and behaviors within the Early Check portal using three methods: (1) a feedback survey available to the consenting parent of participating infants (typically mothers), (2) semi-structured interviews conducted with a subset of parents, and (3) Google Analytics. During an approximate 3-year period, 17 936 newborns received normal IRR and there were 27 812 visits to the portal. Most surveyed parents reported viewing their baby's results (86%, 1410/1639). Parents largely found the portal easy to use to get results, and helpful in understanding the results. However, 10% of parents said it was difficult to find enough information to understand their baby's results. In Early Check, providing normal IRR via the portal made a large-scale study practical, and was highly rated by most users. Return of normal IRR may be particularly amenable to web-based portals, as the consequences to participants from not viewing results are modest, and the interpretation of a normal result is relatively straightforward.

Diagnosis of TBC1D32-associated conditions: Expanding the phenotypic spectrum of a complex ciliopathy.

Exome sequencing is a powerful tool in prenatal and postnatal genetics and can help identify novel candidate genes critical to human development. We describe seven unpublished probands with rare likely pathogenic variants or variants of uncertain significance that segregate with recessive disease in TBC1D32, including four fetal probands in three unrelated pedigrees and three pediatric probands in unrelated pedigrees. We also report clinical comparisons with seven previously published patients. Index probands were identified through an ongoing prenatal exome sequencing study and through an online data sharing platform (Gene Matcher™). A literature review was also completed. TBC1D32 is involved in the development and function of cilia and is expressed in the developing hypothalamus and pituitary gland. We provide additional data to expand the phenotype correlated with TBC1D32 variants, including a severe prenatal phenotype associated with life-limiting congenital anomalies.

Endocannabinoid dysfunction in neurological disease: neuro-ocular DAGLA-related syndrome.

The endocannabinoid system is a highly conserved and ubiquitous signalling pathway with broad-ranging effects. Despite critical pathway functions, gene variants have not previously been conclusively linked to human disease. We identified nine children from eight families with heterozygous, de novo truncating variants in the last exon of DAGLA with a neuro-ocular phenotype characterized by developmental delay, ataxia and complex oculomotor abnormality. All children displayed paroxysms of nystagmus or eye deviation accompanied by compensatory head posture and worsened incoordination most frequently after waking. RNA sequencing showed clear expression of the truncated transcript and no differences were found between mutant and wild-type DAGLA activity. Immunofluorescence staining of patient-derived fibroblasts and HEK cells expressing the mutant protein showed distinct perinuclear aggregation not detected in control samples. This report establishes truncating variants in the last DAGLA exon as the cause of a unique paediatric syndrome. Because enzymatic activity was preserved, the observed mislocalization of the truncated protein may account for the observed phenotype. Potential mechanisms include DAGLA haploinsufficiency at the plasma membrane or dominant negative effect. To our knowledge, this is the first report directly linking an endocannabinoid system component with human genetic disease and sets the stage for potential future therapeutic avenues.