Exome and Genome Sequencing to Diagnose the Genetic Basis of Neonatal Hypotonia: An International Consortium Study.

Background And Objectives: Hypotonia is a relatively common finding among infants in the neonatal intensive care unit (NICU). Consideration of genetic testing is recommended early in the care of infants with unexplained hypotonia. We aimed to assess the diagnostic yield and overall impact of exome and genome sequencing (ES and GS).

Recognition of Hyperinsulinaemic Hypoglycaemia in Infants with Congenital Central Hypoventilation Syndrome.

Introduction: Congenital central hypoventilation syndrome (CCHS) is a rare autosomal dominant condition due to mutations in the transcription factor PHOX2B. It is characterized by alveolar hypoventilation with symptoms of autonomic nervous system dysfunction. Hyperinsulinaemic hypoglycaemia (HH) due to glucose dysregulation caused by anomalous insulin secretion has been reported as a feature of CCHS.

POLR3B is associated with a developmental and epileptic encephalopathy with myoclonic-atonic seizures and ataxia.

Objective: POLR3B encodes the second largest subunit of RNA polymerase III, which is essential for transcription of small non-coding RNAs. Biallelic pathogenic variants in POLR3B are associated with an inherited hypomyelinating leukodystrophy. Recently, de novo heterozygous variants in POLR3B were reported in six individuals with ataxia, spasticity, and demyelinating peripheral neuropathy.

Variants in ZFX are associated with an X-linked neurodevelopmental disorder with recurrent facial gestalt.

Pathogenic variants in multiple genes on the X chromosome have been implicated in syndromic and non-syndromic intellectual disability disorders. ZFX on Xp22.11 encodes a transcription factor that has been linked to diverse processes including oncogenesis and development, but germline variants have not been characterized in association with disease.

Further description of two individuals with de novo p.(Glu127Lys) missense variant in the ASCL1 gene.

Achaete-Scute Family basic-helix-loop-helix (bHLH) Transcription Factor 1 (ASCL1) is a proneural transcription factor involved in neuron development in the central and peripheral nervous system. While initially suspected to contribute to congenital central hypoventilation syndrome-1 (CCHS) with or without Hirschsprung disease (HSCR) in three individuals, its implication was ruled out by the presence, in one of the individuals, of a Paired-like homeobox 2B (PHOX2B) heterozygous polyalanine expansion variant, known to cause CCHS. We report two additional unrelated individuals sharing the same sporadic ASCL1 p.

Gain-of-function and loss-of-function variants in GRIA3 lead to distinct neurodevelopmental phenotypes.

AMPA (α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid) receptors (AMPARs) mediate fast excitatory neurotransmission in the brain. AMPARs form by homo- or heteromeric assembly of subunits encoded by the GRIA1-GRIA4 genes, of which only GRIA3 is X-chromosomal. Increasing numbers of GRIA3 missense variants are reported in patients with neurodevelopmental disorders (NDD), but only a few have been examined functionally.

Clinical and molecular characterization of novel FARS2 variants causing neonatal mitochondrial disease.

FARS2 encodes the mitochondrial phenylalanyl-tRNA synthetase (mtPheRS), which is essential for charging mitochondrial (mt-) tRNA with phenylalanine for use in intramitochondrial translation. Many biallelic, pathogenic FARS2 variants have been described previously, which are mostly associated with two distinct clinical phenotypes; an early onset epileptic mitochondrial encephalomyopathy or a later onset spastic paraplegia. In this study, we report on a patient who presented at 3 weeks of age with tachypnoea and poor feeding, which progressed to severe metabolic decompensation with lactic acidosis and seizure activity followed by death at 9 weeks of age.

De novo PHF5A variants are associated with craniofacial abnormalities, developmental delay, and hypospadias.

Purpose: The SF3B splicing complex is composed of SF3B1-6 and PHF5A. We report a developmental disorder caused by de novo variants in PHF5A.

Methods: Clinical, genomic, and functional studies using subject-derived fibroblasts and a heterologous cellular system were performed.

Combined novel homozygous variants in both and STAT presenting with severe combined immune deficiency: case report and literature review.

Background: Sphingosine phosphate lyase insufficiency syndrome (SPLIS) is associated with biallelic variants in , comprising a multisystemic disease characterized by steroid resistant nephrotic syndrome, primary adrenal insufficiency, neurological problems, skin abnormalities and immunodeficiency in described cases. Signal transducer and activator of transcription 1 (STAT1) plays an important role in orchestrating an appropriate immune response through JAK-STAT pathway. Biallelic loss of function (LOF) variants lead to STAT1 deficiency with a severe phenotype of immunodeficiency with increased frequency of infections and poor outcome if untreated.

A novel ELP1 mutation impairs the function of the Elongator complex and causes a severe neurodevelopmental phenotype.

Background: Neurodevelopmental disorders (NDDs) are heterogeneous, debilitating conditions that include motor and cognitive disability and social deficits. The genetic factors underlying the complex phenotype of NDDs remain to be elucidated. Accumulating evidence suggest that the Elongator complex plays a role in NDDs, given that patient-derived mutations in its ELP2, ELP3, ELP4 and ELP6 subunits have been associated with these disorders.

Craniosynostosis, inner ear, and renal anomalies in a child with complete loss of (sprouty homolog 1) function.

Introduction: encodes protein sprouty homolog 1 (Spry-1), a negative regulator of receptor tyrosine kinase signalling. Null mutant mice display kidney/urinary tract abnormalities and altered size of the skull; complete loss-of-function of Spry-1 in humans has not been reported.

Methods: Analysis of whole-genome sequencing data from individuals with craniosynostosis enrolled in the 100,000 Genomes Project identified a likely pathogenic variant within .

Expanding the phenotype of children presenting with hypoventilation with biallelic TBCK pathogenic variants and literature review.

Individuals with biallelic TBCK pathogenic variants present in infancy with distinctive facial features, profound hypotonia, severe intellectual impairment and epilepsy. Although rare, it may mimic other neurogenetic disorders leading to extensive investigations. Improved understanding of the clinical phenotype can support early monitoring of complications due to respiratory insufficiency.

Emerging phenotypes linked to variants in and MIRAGE syndrome.

Background: Heterozygous variants in cause MIRAGE syndrome, a complex multisystem disorder involving Myelodysplasia, Infection, Restriction of growth, Adrenal hypoplasia, Genital phenotypes, and Enteropathy. The range of additional clinical associations is expanding and includes disrupted placental development, poor post-natal growth and endocrine features. Increasingly, milder phenotypic features such as hypospadias in small for gestational age (SGA) boys and normal adrenal function are reported.

SOX11 variants cause a neurodevelopmental disorder with infrequent ocular malformations and hypogonadotropic hypogonadism and with distinct DNA methylation profile.

Purpose: This study aimed to undertake a multidisciplinary characterization of the phenotype associated with SOX11 variants.

Methods: Individuals with protein altering variants in SOX11 were identified through exome and genome sequencing and international data sharing. Deep clinical phenotyping was undertaken by referring clinicians.

Height and body mass index in molecularly confirmed Silver-Russell syndrome and the long-term effects of growth hormone treatment.

Objective: Silver-Russell syndrome (SRS) causes short stature. Growth hormone (GH) treatment aims to increase adult height. However, data are limited on the long-term outcomes of GH in patients with molecularly confirmed SRS.

Multicenter Consensus Approach to Evaluation of Neonatal Hypotonia in the Genomic Era: A Review.

Importance: Infants with hypotonia can present with a variety of potentially severe clinical signs and symptoms and often require invasive testing and multiple procedures. The wide range of clinical presentations and potential etiologies leaves diagnosis and prognosis uncertain, underscoring the need for rapid elucidation of the underlying genetic cause of disease.

Observations: The clinical application of exome sequencing or genome sequencing has dramatically improved the timely yield of diagnostic testing for neonatal hypotonia, with diagnostic rates of greater than 50% in academic neonatal intensive care units (NICUs) across Australia, Canada, the UK, and the US, which compose the International Precision Child Health Partnership (IPCHiP).