Jolanda H. Schieving

Mutations in DDX3X Are a Common Cause of Unexplained Intellectual Disability with Gender-Specific Effects on Wnt Signaling

Intellectual disability (ID) affects approximately 1%-3% of humans with a gender bias toward males. Previous studies have identified mutations in more than 100 genes on the X chromosome in males with ID, but there is less evidence for de novo mutations on the X chromosome causing ID in females. In this study we present 35 unique deleterious de novo mutations in DDX3X identified by whole exome sequencing in 38 females with ID and various other features including hypotonia, movement disorders, behavior problems, corpus callosum hypoplasia, and epilepsy. Based on our findings, mutations in DDX3X are one of the more common causes of ID, accounting for 1%-3% of unexplained ID in females. Although no de novo DDX3X mutations were identified in males, we present three families with segregating missense mutations in DDX3X, suggestive of an X-linked recessive inheritance pattern. In these families, all males with the DDX3X variant had ID, whereas carrier females were unaffected. To explore the pathogenic mechanisms accounting for the differences in disease transmission and phenotype between affected females and affected males with DDX3X missense variants, we used canonical Wnt defects in zebrafish as a surrogate measure of DDX3X function in vivo. We demonstrate a consistent loss-of-function effect of all tested de novo mutations on the Wnt pathway, and we further show a differential effect by gender. The differential activity possibly reflects a dose-dependent effect of DDX3X expression in the context of functional mosaic females versus one-copy males, which reflects the complex biological nature of DDX3X mutations.

Mutations in RARS Cause Hypomyelination

Hypomyelinating disorders of the central nervous system are still a diagnostic challenge, as many patients remain without genetic diagnosis. Using magnetic resonance imaging (MRI) pattern recognition and whole exome sequencing, we could ascertain compound heterozygous mutations in RARS in 4 patients with hypomyelination. Clinical features included severe spasticity and nystagmus. RARS encodes the cytoplasmic arginyl‐tRNA synthetase, an enzyme essential for RNA translation. This protein is among the subunits of the multisynthetase complex, which emerges as a key player in myelination. Ann Neurol 2014;76:134–139

A clinical utility study of exome sequencing versus conventional genetic testing in pediatric neurology

Purpose:Implementation of novel genetic diagnostic tests is generally driven by technological advances because they promise shorter turnaround times and/or higher diagnostic yields. Other aspects, including impact on clinical management or cost-effectiveness, are often not assessed in detail prior to implementation.Methods:We studied the clinical utility of whole-exome sequencing (WES) in complex pediatric neurology in terms of diagnostic yield and costs. We analyzed 150 patients (and their parents) presenting with complex neurological disorders of suspected genetic origin. In a parallel study, all patients received both the standard diagnostic workup (e.g., cerebral imaging, muscle biopsies or lumbar punctures, and sequential gene-by-gene–based testing) and WES simultaneously.Results:Our unique study design allowed direct comparison of diagnostic yield of both trajectories and provided insight into the economic implications of implementing WES in this diagnostic trajectory. We showed that WES identified significantly more conclusive diagnoses (29.3%) than the standard care pathway (7.3%) without incurring higher costs. Exploratory analysis of WES as a first-tier diagnostic test indicates that WES may even be cost-saving, depending on the extent of other tests being omitted.Conclusion:Our data support such a use of WES in pediatric neurology for disorders of presumed genetic origin.Genet Med advance online publication 23 March 2017

The diagnostic pathway in complex paediatric neurology: A cost analysis

BACKGROUND The diagnostic trajectory of complex paediatric neurology may be long, burdensome, and expensive while its diagnostic yield is frequently modest. Improvement in this trajectory is desirable and might be achieved by innovations such as whole exome sequencing. In order to explore the consequences of implementing them, it is important to map the current pathway. To that end, this study assessed the healthcare resource use and associated costs in this diagnostic trajectory in the Netherlands. METHODS Fifty patients presenting with complex paediatric neurological disorders of a suspected genetic origin were included between September 2011 and March 2012. Data on their healthcare resource utilization were collected from the hospital medical charts. Unit prices were obtained from the Dutch Healthcare Authority, the Dutch Healthcare Insurance Board, and the financial administration of the hospital. Bootstrap simulations were performed to determine mean quantities and costs. RESULTS The mean duration of the diagnostic trajectory was 40 months. A diagnosis was established in 6% of the patients. On average, patients made 16 physician visits, underwent four imaging and two neurophysiologic tests, and had eight genetic and 16 other tests. Mean bootstrapped costs per patient amounted to €12,475, of which 43% was for genetic tests (€5,321) and 25% for hospital visits (€3,112). CONCLUSION Currently, the diagnostic trajectories of paediatric patients who have complex neurological disease with a strong suspected genetic component are lengthy, resource-intensive, and low-yield. The data from this study provide a backdrop against which the introduction of novel techniques such as whole exome sequencing should be evaluated.

Altered PLP1 splicing causes hypomyelination of early myelinating structures.

The objective of this study was to investigate the genetic etiology of the X‐linked disorder “Hypomyelination of Early Myelinating Structures” (HEMS).

Understanding the Psychosocial Effects of WES Test Results on Parents of Children with Rare Diseases

The use of whole exome sequencing (WES) for diagnostics of children with rare genetic diseases raises questions about best practices in genetic counselling. While a lot of attention is now given to pre-test counselling procedures for WES, little is known about how parents experience the (positive, negative, or inconclusive) WES results in daily life. To fill this knowledge gap, data were gathered through in-depth interviews with parents of 15 children who underwent WES analysis. WES test results, like results from other genetic tests, evoked relief as well as worries, irrespective of the type of result. Advantages of obtaining a conclusive diagnosis included becoming more accepting towards the situation, being enabled to attune care to the needs of the child, and better coping with feelings of guilt. Disadvantages experienced included a loss of hope for recovery, and a loss by parents of their social network of peers and the effort necessary to re-establish that social network. While parents with conclusive diagnoses were able to re-establish a peer community with the help of social media, parents receiving a possible diagnosis experienced hurdles in seeking peer support, as peers still needed to be identified. These types of psychosocial effects of WES test results for parents are important to take into account for the development of successful genetic counselling strategies.

Evaluating a counselling strategy for diagnostic WES in paediatric neurology: an exploration of parents' information and communication needs

As whole exome sequencing (WES) is just starting to be used as a diagnostic tool in paediatric neurology for children with a neurological disorder, and patient experiences and preferences with regard to counselling are relatively underexplored. This article explores experiences and preferences of parents with pre‐test and post‐test counselling in a trial that uses WES for diagnostics. Second, it maps information and communication needs which exceed the counselling protocol, in order to acquire insight into how it can be improved. Data were gathered through in‐depth interviews with parents of 15 children who were included in the trial. Information and communication needs of parents differed from the protocol with respect to (i) the type and amount of information provided about WES research, (ii) incidental findings, (iii) communication about progress of the study, and (iv) the communication of the results. Furthermore, parents preferred to have more of a communicative exchange with health care providers about their daily struggles and concerns related to their life with a diseased child and wanted to know how a diagnosis could offer help. There are different ways to meet parental needs, but we suggest that assigning a case manager might be a helpful option that deserves further exploration.

Effect of vaccinations on seizure risk and disease course in Dravet syndrome

Objective: To study the effect of vaccination-associated seizure onset on disease course and estimate the risk of subsequent seizures after infant pertussis combination and measles, mumps, and rubella (MMR) vaccinations in Dravet syndrome (DS). Methods: We retrospectively analyzed data from hospital medical files, child health clinics, and the vaccination register for children with DS and pathogenic SCN1A mutations. Seizures within 24 hours after infant whole-cell, acellular, or nonpertussis combination vaccination or within 5 to 12 days after MMR vaccination were defined as “vaccination-associated.” Risks of vaccination-associated seizures for the different vaccines were analyzed in univariable and in multivariable logistic regression for pertussis combination vaccines and by a self-controlled case series analysis using parental seizure registries for MMR vaccines. Disease courses of children with and without vaccination-associated seizure onset were compared. Results: Children who had DS (n = 77) with and without vaccination-associated seizure onset (21% and 79%, respectively) differed in age at first seizure (median 3.7 vs 6.1 months, p < 0.001) but not in age at first nonvaccination-associated seizure, age at first report of developmental delay, or cognitive outcome. The risk of subsequent vaccination-associated seizures was significantly lower for acellular pertussis (9%; odds ratio 0.18, 95% confidence interval [CI] 0.05–0.71) and nonpertussis (8%; odds ratio 0.11, 95% CI 0.02–0.59) than whole-cell pertussis (37%; reference) vaccines. Self-controlled case series analysis showed an increased incidence rate ratio of seizures of 2.3 (95% CI 1.5–3.4) within the risk period of 5 to 12 days following MMR vaccination. Conclusions: Our results suggest that vaccination-associated earlier seizure onset does not alter disease course in DS, while the risk of subsequent vaccination-associated seizures is probably vaccine-specific.

The Genetic Homogeneity of CAPOS Syndrome: Four New Patients With the c.2452G>A (p.Glu818Lys) Mutation in the ATP1A3 Gene

BACKGROUND The clinical syndrome of cerebellar ataxia, areflexia, pes cavus, optic atrophy, and sensorineural hearing loss (CAPOS) was first described 20 years ago, but it was only recently that whole exome sequencing unveiled the causative mutation in the ATP1A3 gene. We present four patients from the seventh and eighth family identified worldwide, provide a critical review of all patients published thus far, and speculate about the pathophysiologic processes underlying the acute neurological manifestations. CLINICAL OBSERVATIONS The individuals presented here experienced one to three paroxysmal, short-lasting episodes in childhood with cerebellar symptoms and signs, hypotonia, ophthalmoparesis, motor weakness, areflexia, and/or lethargy that were consistently associated with febrile illness. An underlying c.2452G>A mutation in the ATP1A3 gene was found in all four individuals. Besides the persisting CAPOS features, other possibly related sequelae included dystonia, myoclonus, and emotional and behavioral changes. After initiation of acetazolamide in two patients, no further episodes occurred. CONCLUSION Targeted sequencing of the ATP1A3 gene is recommended in children exhibiting paroxysmal, fever-induced ataxia and in adults with a more or less stationary or slowly progressive cerebellar syndrome since childhood accompanied by mixed combinations of areflexia, pes cavus, profound visual impairment, and/or sensorineural hearing loss. Similar to some other types of episodic ataxia, acetazolamide may be considered in patients with CAPOS syndrome to prevent or attenuate bouts of ataxia, but this requires further study.

Haploinsufficiency of MeCP2-interacting transcriptional co-repressor SIN3A causes mild intellectual disability by affecting the development of cortical integrity

Numerous genes are associated with neurodevelopmental disorders such as intellectual disability and autism spectrum disorder (ASD), but their dysfunction is often poorly characterized. Here we identified dominant mutations in the gene encoding the transcriptional repressor and MeCP2 interactor switch-insensitive 3 family member A (SIN3A; chromosome 15q24.2) in individuals who, in addition to mild intellectual disability and ASD, share striking features, including facial dysmorphisms, microcephaly and short stature. This phenotype is highly related to that of individuals with atypical 15q24 microdeletions, linking SIN3A to this microdeletion syndrome. Brain magnetic resonance imaging showed subtle abnormalities, including corpus callosum hypoplasia and ventriculomegaly. Intriguingly, in vivo functional knockdown of Sin3a led to reduced cortical neurogenesis, altered neuronal identity and aberrant corticocortical projections in the developing mouse brain. Together, our data establish that haploinsufficiency of SIN3A is associated with mild syndromic intellectual disability and that SIN3A can be considered to be a key transcriptional regulator of cortical brain development.