Utility of genome sequencing in exome-negative pediatric patients with neurodevelopmental phenotypes.

Exome sequencing (ES) has emerged as an essential tool in the evaluation of neurodevelopmental disorders (NDD) of unknown etiology. Genome sequencing (GS) offers advantages over ES due to improved detection of structural, copy number, repeat number and non-coding variants. However, GS is less commonly utilized due to higher cost and more intense analysis. Here, we present nine cases of pediatric NDD that were molecularly diagnosed with GS between 2017 and 2022, following non-diagnostic ES. All individuals presented with global developmental delay or regression. Other features present in our cohort included epilepsy, white matter abnormalities, brain malformation and dysmorphic features. Two cases were diagnosed on GS due to newly described gene-disease relationship or variant reclassification (MAPK8IP3, CHD3). Additional features missed on ES that were later detected on GS were: intermediate-size deletions in three cases who underwent ES that were not validated for CNV detection, pathogenic variants within the non-protein coding genes SNORD118 and RNU7-1, pathogenic variant within the promoter region of GJB1, and a coding pathogenic variant within BCAP31 which was not sufficiently covered on ES. GS following non-diagnostic ES led to the identification of pathogenic variants in this cohort of nine cases, four of which would not have been identified by reanalysis alone.

Nucleotide metabolism, leukodystrophies, and CNS pathology.

The balance between a protective and a destructive immune response can be precarious, as exemplified by inborn errors in nucleotide metabolism. This class of inherited disorders, which mimics infection, can result in systemic injury and severe neurologic outcomes. The most common of these disorders is Aicardi Goutières syndrome (AGS). AGS results in a phenotype similar to "TORCH" infections (Toxoplasma gondii, Other [Zika virus (ZIKV), human immunodeficiency virus (HIV)], Rubella virus, human Cytomegalovirus [HCMV], and Herpesviruses), but with sustained inflammation and ongoing potential for complications. AGS was first described in the early 1980s as familial clusters of "TORCH" infections, with severe neurology impairment, microcephaly, and basal ganglia calcifications (Aicardi & Goutières, Ann Neurol, 1984;15:49-54) and was associated with chronic cerebrospinal fluid (CSF) lymphocytosis and elevated type I interferon levels (Goutières et al., Ann Neurol, 1998;44:900-907). Since its first description, the clinical spectrum of AGS has dramatically expanded from the initial cohorts of children with severe impairment to including individuals with average intelligence and mild spastic paraparesis. This broad spectrum of potential clinical manifestations can result in a delayed diagnosis, which families cite as a major stressor. Additionally, a timely diagnosis is increasingly critical with emerging therapies targeting the interferon signaling pathway. Despite the many gains in understanding about AGS, there are still many gaps in our understanding of the cell-type drivers of pathology and characterization of modifying variables that influence clinical outcomes and achievement of timely diagnosis.