Smith-Magenis Syndrome: Molecular Basis of a Genetic-Driven Melatonin Circadian Secretion Disorder

Exploring an objective measure of overactivity in children with rare genetic syndromes

BACKGROUND

Overactivity is prevalent in several rare genetic neurodevelopmental syndromes, including Smith-Magenis syndrome, Angelman syndrome, and tuberous sclerosis complex, although has been predominantly assessed using questionnaire techniques. Threats to the precision and validity of questionnaire data may undermine existing insights into this behaviour. Previous research indicates objective measures, namely actigraphy, can effectively differentiate non-overactive children from those with attention-deficit hyperactivity disorder. This study is the first to examine the sensitivity of actigraphy to overactivity across rare genetic syndromes associated with intellectual disability, through comparisons with typically-developing peers and questionnaire overactivity estimates.

METHODS

A secondary analysis of actigraphy data and overactivity estimates from The Activity Questionnaire (TAQ) was conducted for children aged 4-15 years with Smith-Magenis syndrome (N=20), Angelman syndrome (N=26), tuberous sclerosis complex (N=16), and typically-developing children (N=61). Actigraphy data were summarized using the M10 non-parametric circadian rhythm variable, and 24-hour activity profiles were modelled via functional linear modelling. Associations between actigraphy data and TAQ overactivity estimates were explored. Differences in actigraphy-defined activity were also examined between syndrome and typically-developing groups, and between children with high and low TAQ overactivity scores within syndromes.

RESULTS

M10 and TAQ overactivity scores were strongly positively correlated for children with Angelman syndrome and Smith-Magenis syndrome. M10 did not substantially differ between the syndrome and typically-developing groups. Higher early morning activity and lower evening activity was observed across all syndrome groups relative to typically-developing peers. High and low TAQ group comparisons revealed syndrome-specific profiles of overactivity, persisting throughout the day in Angelman syndrome, occurring during the early morning and early afternoon in Smith-Magenis syndrome, and manifesting briefly in the evening in tuberous sclerosis complex.

DISCUSSION

These findings provide some support for the sensitivity of actigraphy to overactivity in children with rare genetic syndromes, and offer syndrome-specific temporal descriptions of overactivity. The findings advance existing descriptions of overactivity, provided by questionnaire techniques, in children with rare genetic syndromes and have implications for the measurement of overactivity. Future studies should examine the impact of syndrome-related characteristics on actigraphy-defined activity and overactivity estimates from actigraphy and questionnaire techniques.

Rab11a Controls Cell Shape via C9orf72 Protein: Possible Relationships to Frontotemporal Dementia/Amyotrophic Lateral Sclerosis (FTDALS) Type 1

Abnormal nucleotide insertions of C9orf72, which forms a complex with Smith-Magenis syndrome chromosomal region candidate gene 8 (SMCR8) protein and WD repeat-containing protein 41 (WDR41) protein, are associated with an autosomal-dominant neurodegenerative frontotemporal dementia and/or amyotrophic lateral sclerosis type 1 (FTDALS1). The differentially expressed in normal and neoplastic cells (DENN) domain-containing C9orf72 and its complex with SMCR8 and WDR41 function as a guanine-nucleotide exchange factor for Rab GTP/GDP-binding proteins (Rab GEF, also called Rab activator). Among Rab proteins serving as major effectors, there exists Rab11a. However, it remains to be established which Rab protein is related to promoting or sustaining neuronal morphogenesis or homeostasis. In this study, we describe that the knockdown of Rab11a decreases the expression levels of neuronal differentiation marker proteins, as well as the elongation of neurite-like processes, using N1E-115 cells, a well-utilized neuronal differentiation model. Similar results were obtained in primary cortical neurons. In contrast, the knockdown of Rab11b, a Rab11a homolog, did not significantly affect their cell morphological changes. It is of note that treatment with hesperetin, a citrus flavonoid (also known as Vitamin P), recovered the neuronal morphological phenotypes induced by Rab11a knockdown. Also, the knockdown of Rab11a or Rab11b led to a decrease in glial marker expression levels and in morphological changes in FBD-102b cells, which serve as the oligodendroglial differentiation model. Rab11a is specifically involved in the regulation of neuronal morphological differentiation. The knockdown effect mimicking the loss of function of C9orf72 is reversed by treatment with hesperetin. These findings may reveal a clue for identifying one of the potential molecular and cellular phenotypes underlying FTDALS1.

Objective and subjective measures of sleep initiation are differentially associated with DNA methylation in adolescents

INTRODUCTION

The onset of puberty is associated with a shift in the circadian timing of sleep, leading to delayed sleep initiation [i.e., later sleep onset time (SOT)] due to later bedtimes and/or longer sleep onset latency (SOL). Several genome-wide association studies (GWAS) have identified genes that may be involved in the etiology of sleep phenotypes. However, circadian rhythms are also epigenetically regulated; therefore, epigenetic biomarkers may provide insight into the physiology of the pubertal sleep onset shift and the pathophysiology of prolonged or delayed sleep initiation.

RESULTS

The gene-wide analysis indicated differential methylation within or around 1818 unique genes across the sleep initiation measurements using self-report, actigraphy (ACT), and polysomnography (PSG), while GWAS-informed analysis yielded 67 genes. Gene hits were identified for bedtime (PSG), SOL (subjective, ACT and PSG) and SOT (subjective and PSG). DNA methylation within 12 genes was associated with both subjective and PSG-measured SOL, 31 with both ACT- and PSG-measured SOL, 19 with both subjective and ACT-measured SOL, and one gene (SMG1P2) had methylation sites associated with subjective, ACT- and PSG-measured SOL.

CONCLUSIONS

Objective and subjective sleep initiation in adolescents is associated with altered DNA methylation in genes previously identified in adult GWAS of sleep and circadian phenotypes. Additionally, our data provide evidence for a potential epigenetic link between habitual (subjective and ACT) SOL and in-lab SOT and DNA methylation in and around genes involved in circadian regulation (i.e., RASD1, RAI1), cardiometabolic disorders (i.e., FADS1, WNK1, SLC5A6), and neuropsychiatric disorders (i.e., PRR7, SDK1, FAM172A). If validated, these sites may provide valuable targets for early detection and prevention of disorders involving prolonged or delayed SOT, such as insomnia, delayed sleep phase, and their comorbidity.

Parkinsonism in Genetic Neurodevelopmental Disorders: A Systematic Review

Background

With advances in clinical genetic testing, associations between genetic neurodevelopmental disorders and parkinsonism are increasingly recognized. In this review, we aimed to provide a comprehensive overview of reports on parkinsonism in genetic neurodevelopmental disorders and summarize findings related to genetic diagnosis, clinical features and proposed disease mechanisms.

Methods

A systematic literature review was conducted in PubMed and Embase on June 15, 2021. Search terms for parkinsonism and genetic neurodevelopmental disorders, using generic terms and the Human Phenotype Ontology, were combined. Study characteristics and descriptive data were extracted from the articles using a modified version of the Cochrane Consumers and Communication Review Group's data extraction template. The protocol was registered in PROSPERO (CRD42020191035).

Results

The literature search yielded 208 reports for data-extraction, describing 69 genetic disorders in 422 patients. The five most reported from most to least frequent were: 22q11.2 deletion syndrome, beta-propeller protein-associated neurodegeneration, Down syndrome, cerebrotendinous xanthomatosis, and Rett syndrome. Notable findings were an almost equal male to female ratio, an early median age of motor onset (26 years old) and rigidity being more common than rest tremor. Results of dopaminergic imaging and response to antiparkinsonian medication often supported the neurodegenerative nature of parkinsonism. Moreover, neuropathology results showed neuronal loss in the majority of cases. Proposed disease mechanisms included aberrant mitochondrial function and disruptions in neurotransmitter metabolism, endosomal trafficking, and the autophagic-lysosomal and ubiquitin-proteasome system.

Conclusion

Parkinsonism has been reported in many GNDs. Findings from this study may provide clues for further research and improve management of patients with GNDs and/or parkinsonism.

Copy number variant analysis for syndromic congenital heart disease in the Chinese population

Background

Syndromic congenital heart disease (CHD) is among the most severe conditions in the pediatric population. Copy number variant (CNV) is an important cause of syndromic CHD, but few studies focused on CNVs related to these patients in China. The present study aimed to identify pathogenic CNVs associated with syndromic CHD in the Chinese population.

Methods

A total of 109 sporadic patients with syndromic CHD were applied chromosomal microarray analysis (CMA). Phenotype spectrum of pathogenic or likely pathogenic CNVs was analyzed. CHD-related genes were prioritized from genes within pathogenic or likely pathogenic CNVs by VarElect, OVA, AMELIE, and ToppGene.

Results

Using CMA, we identified 43 candidate CNVs in 37/109 patients. After filtering CNVs present in the general population, 29 pathogenic/likely pathogenic CNVs in 24 patients were identified. The diagnostic yield of CMA for pathogenic/likely pathogenic CNVs was 23.1% (24/104), excluding 5 cases with aneuploidies or gross chromosomal aberrations. The overlapping analysis of CHD-related gene lists from different prioritization tools highlighted 16 CHD candidate genes.

Conclusion

As the first study focused on CNVs in syndromic CHD from the Chinese population, this study reveals the importance of CMA in exploring the genetic etiology of syndromic CHD and expands our understanding of these complex diseases. The bioinformatic analysis of candidate genes suggests several CHD-related genes for further functional research.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40246-022-00426-8.

Management of Sleep Disturbances Associated with Smith-Magenis Syndrome

Smith-Magenis syndrome is a genetic disorder caused by a microdeletion involving the retinoic acid-induced 1 (RAI1) gene that maps on the short arm of chromosome 17p11.2 or a pathogenic mutation of RAI1. Smith-Magenis syndrome affects patients through numerous congenital anomalies, intellectual disabilities, behavioral challenges, and sleep disturbances. The sleep abnormalities associated with Smith-Magenis syndrome can include frequent nocturnal arousals, early morning awakenings, and sleep attacks during the day. The sleep problems associated with Smith-Magenis syndrome are attributed to haploinsufficiency of the RAI1 gene. One consequence of reduced function of RAI1, and characteristic of Smith-Magenis syndrome, is an inversion of melatonin secretion resulting in a diurnal rather than nocturnal pattern. Treatment of sleep problems in people with Smith-Magenis syndrome generally involves a combination of sleep hygiene techniques, supplemental melatonin, and/or other medications, such as melatonin receptor agonists, β₁-adrenergic antagonists, and stimulant medications, to improve sleep outcomes. Improvement in sleep has been shown to improve behavioral outcomes, which in turn improves the quality of life for both patients and their caregivers.