Bret Bostwick

Metabolic Disruption in Drosophila Bang-Sensitive Seizure Mutants

We examined a number of Drosophila mutants with increased susceptibility to seizures following mechanical or electrical stimulation to better understand the underlying factors that predispose neurons to aberrant activity. Several mutations in this class have been molecularly identified and suggest metabolic disruption as a possible source for increased seizure susceptibility. We mapped the bang-sensitive seizure mutation knockdown (kdn) to cytological position 5F3 and identified citrate synthase as the affected gene. These results further support a role for mitochondrial metabolism in controlling neuronal activity and seizure susceptibility. Biochemical analysis in bang-sensitive mutants revealed reductions in ATP levels consistent with disruption of mitochondrial energy production in these mutants. Electrophysiological analysis of mutants affecting mitochondrial proteins revealed an increased likelihood for a specific pattern of seizure activity. Our data implicate cellular metabolism in regulating seizure susceptibility and suggest that differential sensitivity of neuronal subtypes to metabolic changes underlies distinct types of seizure activity.

Use of Exome Sequencing for Infants in Intensive Care Units: Ascertainment of Severe Single-Gene Disorders and Effect on Medical Management

Importance While congenital malformations and genetic diseases are a leading cause of early infant death, to our knowledge, the contribution of single-gene disorders in this group is undetermined. Objective To determine the diagnostic yield and use of clinical exome sequencing in critically ill infants. Design, Setting, and Participants Clinical exome sequencing was performed for 278 unrelated infants within the first 100 days of life who were admitted to Texas Children’s Hospital in Houston, Texas, during a 5-year period between December 2011 and January 2017. Exome sequencing types included proband exome, trio exome, and critical trio exome, a rapid genomic assay for seriously ill infants. Main Outcomes and Measures Indications for testing, diagnostic yield of clinical exome sequencing, turnaround time, molecular findings, patient age at diagnosis, and effect on medical management among a group of critically ill infants who were suspected to have genetic disorders. Results The mean (SEM) age for infants participating in the study was 28.5 (1.7) days; of these, the mean (SEM) age was 29.0 (2.2) days for infants undergoing proband exome sequencing, 31.5 (3.9) days for trio exome, and 22.7 (3.9) days for critical trio exome. Clinical indications for exome sequencing included a range of medical concerns. Overall, a molecular diagnosis was achieved in 102 infants (36.7%) by clinical exome sequencing, with relatively low yield for cardiovascular abnormalities. The diagnosis affected medical management for 53 infants (52.0%) and had a substantial effect on informed redirection of care, initiation of new subspecialist care, medication/dietary modifications, and furthering life-saving procedures in select patients. Critical trio exome sequencing revealed a molecular diagnosis in 32 of 63 infants (50.8%) at a mean (SEM) of 33.1 (5.6) days of life with a mean (SEM) turnaround time of 13.0 (0.4) days. Clinical care was altered by the diagnosis in 23 of 32 patients (71.9%). The diagnostic yield, patient age at diagnosis, and medical effect in the group that underwent critical trio exome sequencing were significantly different compared with the group who underwent regular exome testing. For deceased infants (n = 81), genetic disorders were molecularly diagnosed in 39 (48.1%) by exome sequencing, with implications for recurrence risk counseling. Conclusions and Relevance Exome sequencing is a powerful tool for the diagnostic evaluation of critically ill infants with suspected monogenic disorders in the neonatal and pediatric intensive care units and its use has a notable effect on clinical decision making.

Chronic Oral l-Carnitine Supplementation Drives Marked Plasma TMAO Elevations in Patients with Organic Acidemias Despite Dietary Meat Restrictions

Recent studies have implicated trimethylamine N-oxide (TMAO) in atherosclerosis, raising concern about L-carnitine, a common supplement for patients with inborn errors of metabolism (IEMs) and a TMAO precursor metabolized, in part, by intestinal microbes. Dietary meat restriction attenuates carnitine-to-TMAO conversion, suggesting that TMAO production may not occur in meat-restricted individuals taking supplemental L-carnitine, but this has not been tested. Here, we mine a metabolomic dataset to assess TMAO levels in patients with diverse IEMs, including organic acidemias. These data were correlated with clinical information and confirmed using a quantitative TMAO assay. Marked plasma TMAO elevations were detected in patients treated with supplemental L-carnitine, including those on a meat-free diet. On average, patients with an organic acidemia had ~45-fold elevated [TMAO], as compared to the reference population. This effect was mitigated by metronidazole therapy lasting 7 days each month. Collectively, our data show that TMAO production occurs at high levels in patients with IEMs receiving oral L-carnitine. Further studies are needed to determine the long-term safety and efficacy of chronic oral L-carnitine supplementation and whether suppression or circumvention of intestinal bacteria may improve L-carnitine therapy.

Phenotypic and molecular characterization of focal dermal hypoplasia in 18 individuals

Focal dermal hypoplasia, or Goltz syndrome, is a highly variable X‐linked dominant disorder with abnormalities in ectoderm and mesoderm derived tissues. Classic clinical features include patchy hypoplastic skin, split hand/foot deformities, and ocular malformations. We aimed to refine the understanding of the phenotypic spectrum and natural history of this disorder and now present multi‐disciplinary clinical description and medical history review for 18 patients with focal dermal hypoplasia. All disease characteristics were analyzed and compiled in aggregate to aid in development of clinical diagnostic criteria. Medical history data unexpectedly revealed that the majority of patients (87%) had undergone tonsillectomy for obstructive sleep apnea, which exposed an important co‐morbidity that is not well described in the literature, but managing physicians should be made aware of. Fifteen of the 18 patients underwent molecular sequencing of PORCN to detect heterozygous or mosaic mutations. Where no mutation was detected, we performed exon‐targeted chromosomal microarray to evaluate for large deletions of the PORCN gene region. We detected a pathogenic genotype in 14 of 15 patients, including one novel chromosomal deletion and four novel PORCN sequence variants. Here, we provide phenotypic summary analysis of 18 patients with focal dermal hypoplasia and propose clinical diagnostic criteria.

Focal Dermal Hypoplasia

Focal dermal hypoplasia in five sisters and their mother is presented. The lesions present in this family and in eight additional Mexican cases are reviewed. Fourteen out of 15 cases were females and two were males. All cases had cutaneous lesions, clinically typical of focal dermal hypoplasia; these were confirmed histologically. Osseous changes and syndactyly were the more frequently associated lesions. The resemblance of this syndrome to incontinentia pigmenti and to aplasia cutis congenita is stressed. The study of this family, together with five families reported in the literature, suggests X-linked dominant inheritance with lethality in males. The known male cases could represent occasional survival or genetic heterogeneity.

A Drosophila behavioral mutant, down and out (dao), is defective in an essential regulator of Erg potassium channels

To signal properly, excitable cells must establish and maintain the correct balance of various types of ion channels that increase or decrease membrane excitability. The mechanisms by which this balance is regulated remain largely unknown. Here, we describe a regulatory mechanism uncovered by a Drosophila behavioral mutant, down and out (dao). At elevated temperatures, dao loss-of-function mutants exhibit seizures associated with spontaneous bursts of neural activity. This phenotype closely resembles that of seizure mutations, which impair activity of ether-a-go-go-related gene (Erg)-type potassium channels. Conversely, neural over-expression of wild-type Dao confers dominant temperature-sensitive paralysis with kinetics reminiscent of paralytic sodium-channel mutants. The over-expression phenotype of dao is suppressed in a seizure mutant background, suggesting that Dao acts by an effect on Erg channels. In support of this hypothesis, functional expression of Erg channels in a heterologous system is dependent on the presence of Dao. These results indicate that Dao has an important role in establishing the proper level of neuronal membrane excitability by regulating functional expression of Erg channels.

Phenotypic and molecular characterisation of CDK13-related congenital heart defects, dysmorphic facial features and intellectual developmental disorders

BackgroundDe novo missense variants in CDK13 have been described as the cause of syndromic congenital heart defects in seven individuals ascertained from a large congenital cardiovascular malformations cohort. We aimed to further define the phenotypic and molecular spectrum of this newly described disorder.MethodsTo minimise ascertainment bias, we recruited nine additional individuals with CDK13 pathogenic variants from clinical and research exome laboratory sequencing cohorts. Each individual underwent dysmorphology exam and comprehensive medical history review.ResultsWe demonstrate greater than expected phenotypic heterogeneity, including 33% (3/9) of individuals without structural heart disease on echocardiogram. There was a high penetrance for a unique constellation of facial dysmorphism and global developmental delay, as well as less frequently seen renal and sacral anomalies. Two individuals had novel CDK13 variants (p.Asn842Asp, p.Lys734Glu), while the remaining seven unrelated individuals had a recurrent, previously published p.Asn842Ser variant. Summary of all variants published to date demonstrates apparent restriction of pathogenic variants to the protein kinase domain with clustering in the ATP and magnesium binding sites.ConclusionsHere we provide detailed phenotypic and molecular characterisation of individuals with pathogenic variants in CDK13 and propose management guidelines based upon the estimated prevalence of anomalies identified.

Schaaf‐Yang syndrome overview: Report of 78 individuals

Schaaf‐Yang Syndrome (SYS) is a genetic disorder caused by truncating pathogenic variants in the paternal allele of the maternally imprinted, paternally expressed gene MAGEL2, located in the Prader‐Willi critical region 15q11‐15q13. SYS is a neurodevelopmental disorder that has clinical overlap with Prader‐Willi Syndrome in the initial stages of life but becomes increasingly distinct throughout childhood and adolescence. Here, we describe the phenotype of an international cohort of 78 patients with nonsense or frameshift mutations in MAGEL2. This cohort includes 43 individuals that have been reported previously, as well as 35 newly identified individuals with confirmed pathogenic genetic variants. We emphasize that intellectual disability/developmental delay, autism spectrum disorder, neonatal hypotonia, infantile feeding problems, and distal joint contractures are the most consistently shared features of patients with SYS. Our results also indicate that there is a marked prevalence of infantile respiratory distress, gastroesophageal reflux, chronic constipation, skeletal abnormalities, sleep apnea, and temperature instability. While there are many shared features, patients with SYS are characterized by a wide phenotypic spectrum, including a variable degree of intellectual disability, language development, and motor milestones. Our results indicate that the variation in phenotypic severity may depend on the specific location of the truncating mutation, suggestive of a genotype–phenotype association. This evidence may be useful in both prenatal and pediatric genetic counseling.

The first reported case of an inherited pathogenic CHD2 variant in a clinically affected mother and daughter

Pathogenic variants in CHD2 (chromodomain helicase DNA‐binding protein 2) have been reported in neurodevelopmental disorders with a broad spectrum of phenotypic variability, ranging from mild intellectual disability to atonic‐myoclonic epilepsy. However, given the paucity of reported cases the extent of this phenotypic spectrum is currently unknown. Furthermore, all confirmed pathogenic CHD2 variants reported to date have been de novo, preventing the study of intrafamilial phenotypic heterogeneity and creating ambiguity regarding recurrence risk, penetrance, and expressivity. Here, we report the first known case of an inherited pathogenic CHD2 variant in affected mother and daughter. This case demonstrates intrafamilial phenotypic heterogeneity and confirms potential heritability of CHD2‐related neurodevelopmental disorders.