Untangling neurodevelopmental disorders in the adulthood: a movement disorder is the clue

Paired copy number variation analysis in siblings discordant for familial Parkinson's disease

ObjectivesNumerous studies on the genetic pathogenesis of familial Parkinson's Disease (PD) have explained the etiology of only a limited percentage of cases. In this study, we aimed to identify copy number variations (CNVs) in patients with familial PD compared to their healthy siblings.MethodsGenomic microarray analysis was performed using the CytoScan HD array platform, and paired copy number variation analysis was performed using Partek Genomics Suite.ResultsA total of 211 CNVs were detected in patients (genomic markers per CNV >10, markers per base pair >0.0005). Genes localized in CNV regions were enriched in the "Metabolism of xenobiotics by cytochrome P450" pathway. Subsequently, CNVs located in regions with segmental duplication, large genomic gap or "dosage sensitivity unlikely," with a frequency higher than 0.01%, and found to be "both amplified and deleted" in patients were excluded. Genes potentially affected by exonic copy number losses were HPGDS, TUBB8, ZMYND11, FLI-1, THADA, FAM47E, FAM47E-STBD1, AGMO, CYRIB, and MIR5194, while the detected copy number gains included the exons of the PCSK6, MIR4522, WSB1, C8orf44-SGK3, SGK3, and MCMDC2. No copy number variations were detected on chromosomes 13 and 18.ConclusionsHere, we report the results of the first paired CNV analysis in siblings discordant for Familial Parkinson's Disease. Validation and frequency determination of rare and novel CNVs identified in larger familial PD cohorts may reveal novel PD risk genes. The metabolism of xenobiotics by cytochrome P450 pathway deserves further functional and translational studies in familial Parkinson's disease.

Epigenetic Regulation and Neurodevelopmental Disorders: From MeCP2 to the TCF20/PHF14 Complex

BACKGROUND

Neurodevelopmental disorders (NDDs) affect approximately 15% of children and adolescents worldwide. This group of disorders is often polygenic with varying risk factors, with many associated genes converging on shared molecular pathways, including chromatin regulation and transcriptional control. Understanding how NDD-associated chromatin regulators and protein complexes orchestrate these regulatory pathways is crucial for elucidating NDD pathogenesis and developing targeted therapeutic strategies. Recently, the TCF20/PHF14 chromatin complex was identified in the mammalian brain, expanding the list of chromatin regulatory remodelers implicated in NDDs. This complex-which includes MeCP2, RAI1, TCF20, PHF14, and HMG20A-plays a vital role in epigenetic and transcriptional regulation.

METHODS

We review and summarize current research and clinical reports pertaining to the different components of the MeCP2-interacting TCF20/PHF14 complex. We examine the NDDs associated with the TCF20/PHF14 complex, explore the molecular and neuronal functions of its components, and discuss emerging therapeutic strategies targeting this complex to mitigate symptoms, with broader applicability to other NDDs.

RESULTS

Mutations in the genes encoding the components of the MeCP2-interacting TCF20/PHF14 complex have been linked to various NDDs, underscoring its critical contribution to brain development and NDD pathogenesis.

CONCLUSIONS

The MeCP2-interacting TCF20/PHF14 complex and its associated NDDs could serve as a model system to provide insight into the interplay between epigenetic regulation and NDD pathogenesis.

Expanding the mutational spectrum of ZTTK syndrome: A de novo variant with global developmental delay and malnutrition in a Chinese patient

BACKGROUND

Zhu-Tokita-Takenouchi-Kim (ZTTK, OMIM 617140) syndrome is a severe multisystem developmental disorder characterized by intellectual disability, developmental delay, cortical malformations, epilepsy, visual problems, musculoskeletal abnormalities, and congenital malformations. ZTTK syndrome is caused by a heterozygous pathogenic variant of the SON gene (NM_138927) at chromosome 21q22.1. The purpose of this study was to investigate the pathogenesis of a 6-month-old Chinese child who exhibited global developmental delay, muscle weakness, malnutrition, weight loss, and strabismus, brain abnormality, immunological system abnormalities.

METHODS

The little girl was tested for medical exome sequencing (MES) and mtDNA sequencing in trio. And, the mutation was validated by Sanger sequencing.

RESULTS

A novel de novo frameshift variant, c.1845_1870del26 (p.G616Sfs*61), in the SON gene was found in the proband.

CONCLUSION

We described a 6-month-old Chinese child with global developmental delay caused by pathogenic de novo mutation c.1845_1870del26 (p.G616Sfs*61) in the SON. Apart from a founder mutation, we reviewed the phenotypic abnormalities and genotypes in 79 individuals. The data showed that global developmental delay is accompanied by other system disorders. Our findings expanded the mutational spectrum of ZTTK syndrome and provide genetic counseling of baby with global developmental delay.

SON-Related Zhu-Tokita-Takenouchi-Kim Syndrome With Recurrent Hemiplegic Migraine: Putative Role of PRRT2

Background and Objectives

Zhu-Tokita-Takenouchi-Kim (ZTTK) syndrome (OMIM 617140) is a recently identified neurodevelopmental disorder caused by heterozygous loss-of-function (LoF) variants in SON. Because the SON protein functions as an RNA-splicing regulator, it has been shown that some clinical features of ZTTK syndrome can be attributed to abnormal RNA splicing. Several neurologic features have been observed in patients with ZTTK syndrome, including seizure/epilepsy and other EEG abnormalities. However, a relationship between SON LoF in ZTTK syndrome and hemiplegic migraine remains unknown.

Methods

We identified a patient with a pathogenic variant in SON who shows typical clinical features of ZTTK syndrome and experienced recurrent episodes of hemiplegic migraine. To define clinical features, brain MRI and EEG during and after episodes of hemiplegic migraine were characterized. To identify molecular mechanisms for this clinical presentation, we investigated the impact of small interfering RNA (siRNA)-mediated SON knockdown on mRNA expression of the CACNA1A, ATP1A2, SCN1A, and PRRT2 genes, known to be associated with hemiplegic migraine, by quantitative RT-PCR. Pre-mRNA splicing of PRRT2 on SON knockdown was further examined by RT-PCR using primers targeting specific exons.

Results

Recurrent episodes of hemiplegic migraine in our patient typically followed modest closed head injuries, and recurrent seizures occurred during the most severe of these episodes. Transient hemispheric cortical interstitial edema and asymmetric EEG slowing were identified during episodes. Our siRNA experiments revealed that SON knockdown significantly reduces PRRT2 mRNA levels in U87MG and SH-SY5Y cell lines, although a reduction in CACNA1A, ATP1A2, and SCN1A mRNA expression was not observed. We further identified that SON knockdown leads to failure in intron 2 removal from PRRT2 pre-mRNA, resulting in a premature termination codon that blocks the generation of functionally intact full-length PRRT2.

Discussion

This report identifies recurrent hemiplegic migraine as a novel clinical manifestation of ZTTK syndrome, further characterizes this clinical feature, and provides evidence for downregulation of PRRT2 caused by SON LoF as a mechanism causing hemiplegic migraine. Examination of the SON gene may be indicated in individuals with recurrent hemiplegic migraine.

Transgenic mice overexpressing mutant TDP-43 show aberrant splicing of neurological disorders-associated gene Zmynd11 prior to onset of motor symptoms

Mutations in TDP-43 are known to cause Amyotrophic Lateral Sclerosis (ALS) and Frontotemporal Dementia (FTD). TDP-43 binds to and regulates splicing of several RNA including Zmynd11 . Zmynd11 is a transcriptional repressor and a potential E3 ubiquitin ligase family member, known for its role in neuron and muscle differentiation. Mutations in Zmynd11 have been associated with autism with significant developmental motor delays, intellectual disability, and ataxia. Here, we show that Zmynd11 is aberrantly spliced in the brain and spinal cord of transgenic mice overexpressing a mutant human TDP-43 (A315T), and that these changes occur before the onset of motor symptoms.