Cockayne Syndrome due to a maternally-inherited whole gene deletion of ERCC8 and a paternally-inherited ERCC8 exon 4 deletion

Biallelic structural variants in three patients with ERCC8-related Cockayne syndrome and a potential pitfall of copy number variation analysis

Cockayne syndrome (CS) is a rare autosomal recessive disorder caused by mutations in ERCC8 or ERCC6. Most pathogenic variants in ERCC8 are single nucleotide substitutions. Structural variants (SVs) have been reported in patients with ERCC8-related CS. However, comprehensive molecular detection, including SVs of ERCC8, in CS patients remains problematic. Herein, we present three Japanese patients with ERCC8-related CS in whom causative SVs were identified using whole-exome-based copy number variation (CNV) detection tools. One patient showed compound heterozygosity for a 259-kb deletion and a deletion of exon 4 which has previously been reported as an Asia-specific variant. The other two patients were homozygous for the same exon 4 deletion. The exon 4 deletion was detected only by the ExomeDepth software. Intrigued by the discrepancy in the detection capability of various tools for the SVs, we evaluated the analytic performance of four whole-exome-based CNV detection tools using an exome data set from 337 healthy individuals. A total of 1,278,141 exons were predicted as being affected by the 4 CNV tools. Interestingly 95.1% of these affected exons were detected by one tool alone. Thus, we expect that the use of multiple tools may improve the detection rate of SVs from aligned exome data.

The oxidative aging model integrated various risk factors in type 2 diabetes mellitus at system level

Background

Type 2 diabetes mellitus (T2DM) is a chronic endocrine metabolic disease caused by insulin dysregulation. Studies have shown that aging-related oxidative stress (as "oxidative aging") play a critical role in the onset and progression of T2DM, by leading to an energy metabolism imbalance. However, the precise mechanisms through which oxidative aging lead to T2DM are yet to be fully comprehended. Thus, it is urgent to integrate the underlying mechanisms between oxidative aging and T2DM, where meaningful prediction models based on relative profiles are needed.

Methods

First, machine learning was used to build the aging model and disease model. Next, an integrated oxidative aging model was employed to identify crucial oxidative aging risk factors. Finally, a series of bioinformatic analyses (including network, enrichment, sensitivity, and pan-cancer analyses) were used to explore potential mechanisms underlying oxidative aging and T2DM.

Results

The study revealed a close relationship between oxidative aging and T2DM. Our results indicate that nutritional metabolism, inflammation response, mitochondrial function, and protein homeostasis are key factors involved in the interplay between oxidative aging and T2DM, even indicating key indices across different cancer types. Therefore, various risk factors in T2DM were integrated, and the theories of oxi-inflamm-aging and cellular senescence were also confirmed.

Conclusion

In sum, our study successfully integrated the underlying mechanisms linking oxidative aging and T2DM through a series of computational methodologies.

Increased insulin sensitivity and diminished pancreatic beta-cell function in DNA repair deficient Ercc1d/- mice

BACKGROUND

Type 2 diabetes (T2DM) is an age-associated disease characterized by hyperglycemia due to insulin resistance and decreased beta-cell function. DNA damage accumulation has been associated with T2DM, but whether DNA damage plays a role in the pathogenesis of the disease is unclear. Here, we used mice deficient for the DNA excision-repair gene Ercc1 to study the impact of persistent endogenous DNA damage accumulation on energy metabolism, glucose homeostasis and beta-cell function.

METHODS

ERCC1-XPF is an endonuclease required for multiple DNA repair pathways and reduced expression of ERCC1-XPF causes accelerated accumulation of unrepaired endogenous DNA damage and accelerated aging in humans and mice. In this study, energy metabolism, glucose metabolism, beta-cell function and insulin sensitivity were studied in Ercc1^d/- mice, which model a human progeroid syndrome.

RESULTS

Ercc1^d/- mice displayed suppression of the somatotropic axis and altered energy metabolism. Insulin sensitivity was increased, whereas, plasma insulin levels were decreased in Ercc1^d/- mice. Fasting induced hypoglycemia in Ercc1^d/- mice, which was the result of increased glucose disposal. Ercc1^d/- mice exhibit a significantly reduced beta-cell area, even compared to control mice of similar weight. Glucose-stimulated insulin secretion in vivo was decreased in Ercc1^d/- mice. Islets isolated from Ercc1^d/- mice showed increased DNA damage markers, decreased glucose-stimulated insulin secretion and increased susceptibility to apoptosis.

CONCLUSION

Spontaneous DNA damage accumulation triggers an adaptive response resulting in improved insulin sensitivity. Loss of DNA repair, however, does negatively impacts beta-cell survival and function in Ercc1^d/- mice.

Molecular spectrum of excision repair cross-complementation group 8 gene defects in Chinese patients with Cockayne syndrome type A

There are two genetics complementary groups Cockayne syndrome type A and B (CS-A and CS-B OMIM 216400, 133540), which is a rare autosomal recessive segmental progeroid syndrome. Homozygous or compound heterozygous mutations in the excision repair cross-complementation group 8 gene (ERCC8) result in CS-A, and mutations in ERCC6 result in CS-B. Homozygous ERCC6/ERCC8 mutations also result in UV-sensitive syndrome. In this study, twenty-one Han Chinese patients with CS were investigated to identify mutations in ERCC8/ERCC6, of which thirteen cases with CS-A were identified with the mutations of ERCC8. There are five types mutations of ERCC8 in our study, such as exon 4 rearrangement, c.394_398delTTACA, c.299insA, c.843 + 2 T > C, and c.2 T > A. An estimated frequency of exon 4 rearrangement accounts for 69.23% and c.394_398delTTACA accounts for 11.53% in our cohort. Haplotype analysis revealed that the exon 4 rearrangement and c.394_398delTTACA mutations originated from a common founder in the Chinese population respectively. With the identification of three novel ERCC8 mutations, this study expanded the molecular spectrum of known ERCC8 defects, and furthermore, suggests that the exon 4 rearrangement and c.394_398delTTACA mutations may be a common underlying cause of CS-A in the Chinese population, which is different from that in other populations.

A complex intragenic rearrangement of ERCC8 in Chinese siblings with Cockayne syndrome

Cockayne syndrome is an autosomal recessive disorder principally characterized by postnatal growth failure and progressive neurological dysfunction, due primarily to mutations in ERCC6 and ERCC8. Here, we report our diagnostic experience for two patients in a Chinese family suspected on clinical grounds to have Cockayne syndrome. Using multiple molecular techniques, including whole exome sequencing, array comparative genomic hybridization and quantitative polymerase chain reaction, we identified compound heterozygosity for a maternal splicing variant (chr5:60195556, NM_000082:c.618-2A > G) and a paternal complex deletion/inversion/deletion rearrangement removing exon 4 of ERCC8, confirming the suspected pathogenesis in these two subjects. Microhomology (TAA and AGCT) at the breakpoints indicated that microhomology-mediated FoSTeS events were involved in this complex ERCC8 rearrangement. This diagnostic experience illustrates the value of high-throughput genomic technologies combined with detailed phenotypic assessment in clinical genetic diagnosis.