TBC1D24-related familial infantile multifocal myoclonus: Description of a new Chinese pedigree with a 20 year follow up

Incomplete Trisomy Rescue Reveals the Mechanism Underlying Discordance Between Noninvasive Prenatal Screening and Prenatal Diagnosis

BACKGROUND

Uniparental disomy (UPD) is a specific type of chromosomal variation in which both chromosomes of a homologous pair are inherited from the same parent. It is responsible for a wide range of disorders. Monosomy rescue and trisomy rescue are the two main hypotheses of UPD generation.

METHODS

An older parturient woman with a positive noninvasive prenatal screening (NIPS) test but a negative prenatal diagnosis was referred to the hospital. Trio whole exome sequencing (trio-WES) and ddPCR were further performed.

RESULTS

Utilizing Trio-WES analysis, our research identified a maternal segmental UPD on chromosome 16, characterized by isodisomic genomic segments at the ends of the chromosome arms and heterodisomic genomic segments near the centromere. Moreover, several nuanced signs pointing to the paternal chromosome 16 were discovered, suggesting a low level of trisomy 16 mosaicism. A homozygous missense mutation (c.1499C>T; p.Ala500Val) was also detected in the fetal TBC1D24 gene, passed down from the heterozygous carrier mother. Furthermore, ddPCR analysis verified a 3% mosaic level of trisomy 16.

CONCLUSION

We have quantitatively verified for the first time a combination of trisomy 16 mosaicism and maternal segmental UPD 16 due to incomplete trisomy rescue, illuminating the cause of the mismatch between positive NIPS and negative prenatal diagnoses.

The Muddle of Myoclonus: Many Guises, 2 Disciplines, Consensus Needed

Myoclonus is often approached in different ways by epileptologists and movement disorder specialists, leading to confusion in the literature. Multiplicity and inconsistency over the past 2 centuries resulted in a lack of precision and ambiguity of the terminology. We show that this is a current problem in which one phenomenon has been described with many terms and vice versa. Of more importance, we discuss the conceptualization of myoclonus from perspectives of both fields and focus on the borderland that exists, especially in the spectrum of cortical and epileptic myoclonus. By giving 2 examples, we illustrate the conundrum: the spectrum of progressive myoclonus epilepsies and progressive myoclonic ataxias and "cortical tremor" observed in familial cortical myoclonic tremor with epilepsy or familial adult myoclonic epilepsy. We attempt to facilitate to bridge these subspecialties and form the base for a uniform understanding to take this issue forward toward future classifications, discussions, and scientific research.

Genetic Links to Episodic Movement Disorders: Current Insights

Episodic or paroxysmal movement disorders (PxMD) are conditions, which occur episodically, are transient, usually have normal interictal periods, and are characterized by hyperkinetic disorders, including ataxia, chorea, dystonia, and ballism. Broadly, these comprise paroxysmal dyskinesias (paroxysmal kinesigenic and non-kinesigenic dyskinesia [PKD/PNKD], paroxysmal exercise-induced dyskinesias [PED]) and episodic ataxias (EA) types 1-9. Classification of paroxysmal dyskinesias has traditionally been clinical. However, with advancement in genetics and the discovery of the molecular basis of several of these disorders, it is becoming clear that phenotypic pleiotropy exists, that is, the same variant may give rise to a variety of phenotypes, and the classical understanding of these disorders requires a new paradigm. Based on molecular pathogenesis, paroxysmal disorders are now categorized as synaptopathies, transportopathies, channelopathies, second-messenger related disorders, mitochondrial or others. A genetic paradigm also has an advantage of identifying potentially treatable disorders, such as glucose transporter 1 deficiency syndromes, which necessitates a ketogenic diet, and ADCY5-related disorders, which may respond to caffeine. Clues for a primary etiology include age at onset below 18 years, presence of family history and fixed triggers and attack duration. Paroxysmal movement disorder is a network disorder, with both the basal ganglia and the cerebellum implicated in pathogenesis. Abnormalities in the striatal cAMP turnover pathway may also be contributory. Although next-generation sequencing has restructured the approach to paroxysmal movement disorders, the genetic underpinnings of several entities remain undiscovered. As more genes and variants continue to be reported, these will lead to enhanced understanding of pathophysiological mechanisms and precise treatment.

An analysis of the significance of the Tre2/Bub2/CDC 16 (TBC) domain protein family 8 in colorectal cancer

The TBC (Tre-2/Bub2/Cdc16, TBC) structural domain is now considered as one of the factors potentially regulating tumor progression. However, to date, studies on the relationship between TBC structural domains and tumors are limited. In this study, we identified the role of TBC1 domain family member 8 (TBC1D8) as an oncogene in colorectal cancer (CRC) by least absolute shrinkage and selection operator (LASSO) and Cox regression analysis, showing that TBC1D8 may independently predict CRC outcome. Functional enrichment and single-cell analysis showed that TBC1D8 levels were associated with hypoxia. TBC1D8 levels were also positively correlated with M2 macrophage infiltration, which may have a complex association with hypoxia. Taken together, these results show that the TBC1D8 gene is involved in colorectal carcinogenesis, and the underlying molecular mechanisms may include hypoxia and immune cell infiltration.