Anhedonia but not passive floating is an indicator of depressive-like behavior in two chronic stress paradigms

Depression is the most common form of mental disability in the world. Depressive episodes may be precipitated by severe acute stressful events or by mild chronic stressors. Studies on the mechanisms of depression require both appropriate experimental models (most of them based on the exposure of animals to chronic stressors), and appropriate tests for assessment of depressive states. In this study male Wistar rats were exposed to two different chronic stress paradigms: an eight-week chronic unpredictable mild stress or a two-week combined chronic stress. The behavioral effects of stress were evaluated using sucrose preference, forced swim and open field tests. After the exposure to chronic unpredictable mild stress, anhedonia was developed, activity in the open field increased, while no changes in the duration of passive floating could be detected. After chronic combined stress, anhedonia was also evident, whereas behavior in the open field and forced swim test did not change. The levels of corticosterone in the blood and brain structures involved in stress-response did not differ from control in both experiments. The absence of significant changes in corticosterone levels and passive floating may be indicative of the adaptation of animals to chronic stress. Anhedonia appears to be a more sensitive indicator of depressive-like behavioral effects of chronic stress as compared to behavior in the forced swim or open field tests.

Biallelic variants in TMEM222 cause a new autosomal recessive neurodevelopmental disorder

PURPOSE

To elucidate the novel molecular cause in families with a new autosomal recessive neurodevelopmental disorder.

METHODS

A combination of exome sequencing and gene matching tools was used to identify pathogenic variants in 17 individuals. Quantitative reverse transcription polymerase chain reaction (RT-qPCR) and subcellular localization studies were used to characterize gene expression profile and localization.

RESULTS

Biallelic variants in the TMEM222 gene were identified in 17 individuals from nine unrelated families, presenting with intellectual disability and variable other features, such as aggressive behavior, shy character, body tremors, decreased muscle mass in the lower extremities, and mild hypotonia. We found relatively high TMEM222 expression levels in the human brain, especially in the parietal and occipital cortex. Additionally, subcellular localization analysis in human neurons derived from induced pluripotent stem cells (iPSCs) revealed that TMEM222 localizes to early endosomes in the synapses of mature iPSC-derived neurons.

CONCLUSION

Our findings support a role for TMEM222 in brain development and function and adds variants in the gene TMEM222 as a novel underlying cause of an autosomal recessive neurodevelopmental disorder.

[Massive parallel sequencing for molecular-genetic diagnosis of mental retardation]

Gene mutations occur with high frequency in children with mental retardation. Standard diagnostic methods, such as TMS, Sanger's sequencing of individual genes, MLPA analysis of deletions, and investigation of methylation status in Martin-Bell syndrome are not informative in the majority of cases that hampered further diagnostic efforts. Massive parallel sequencing (MPS) allowed physicians to continue diagnostic search in previously undiagnosed cases and to find molecular causes of disease. MPS permits to discover a large number of new genes and understand the pathogenesis of mental retardation and brain development more deeply. It became possible to perform prenatal and pre-implantation diagnostics. However, big data generate big problems with their interpretation the genetic counselor faces with. This review reflects the advantages and disadvantages of MPS. Different variants of MPS, including gene panels, whole exome and whole genome sequencing as well as sequencing of trios, are described. In addition, the authors discuss the difficulties of interpretation of the results and recommendations for obtaining the most accurate results.