Analysis of the threshold liability model provides new understanding of causation in autoimmune diseases

Postzygotic Somatic Mutations in the Human Brain Expand the Threshold-Liability Model of Schizophrenia

The search for what causes schizophrenia has been onerous. This research has included extensive assessment of a variety of genetic and environmental factors using ever emerging high-resolution technologies and traditional understanding of the biology of the brain. These efforts have identified a large number of schizophrenia-associated genes, some of which are altered by mutational and epi-mutational mechanisms in a threshold liability model of schizophrenia development. The results, however, have limited predictability and the actual cause of the disease remains unknown. This current state asks for conceptualizing the problem differently in light of novel insights into the nature of mutations, the biology of the brain and the fine precision and resolution of emerging technologies. There is mounting evidence that mutations acquired during postzygotic development are more common than germline mutations. Also, the postzygotic somatic mutations including epimutations (PZMs), which often lead to somatic mosaicism, are relatively common in the mammalian brain in comparison to most other tissues and PZMs are more common in patients with neurodevelopmental mental disorders, including schizophrenia. Further, previously inaccessible, detection of PZMs is becoming feasible with the advent of novel technologies that include single-cell genomics and epigenomics and the use of exquisite experimental designs including use of monozygotic twins discordant for the disease. These developments allow us to propose a working hypothesis and expand the threshold liability model of schizophrenia that already encompasses familial genetic, epigenetic and environmental factors to include somatic de novo PZMs. Further, we offer a test for this expanded model using currently available genome sequences and methylome data on monozygotic twins discordant for schizophrenia (MZD) and their parents. The results of this analysis argue that PZMs play a significant role in the development of schizophrenia and explain extensive heterogeneity seen across patients. It also offers the potential to convincingly link PZMs to both nervous system health and disease, an area that has remained challenging to study and relatively under explored.

On the power of epigenome-wide association studies using a disease-discordant twin design

Motivation

Many studies have investigated the association between DNA methylation alterations and disease occurrences using two design paradigms, traditional case-control and disease-discordant twins. In the disease-discordant twin design, the affected twin serves as the case and the unaffected twin serves as the control. Theoretically the twin design takes advantage of controlling for the shared genetic make-up, but it is still highly debatable if and how much researchers may benefit from such a design over the traditional case-control design.

Results

In this study, we investigate and compare the power of both designs with simulations. A liability threshold model was used assuming that identical twins share the same genetic contribution with respect to the liability of complex human diseases. Varying ranges of parameters have been used to ensure that the simulation is close to real-world scenarios. Our results reveal that the disease-discordant twin design implies greater statistical power over the traditional case-control design. For diseases with moderate and high heritability (>0.3), the disease-discordant twin design allows for large sample size reductions compared to the ordinary case-control design. Our simulation results indicate that the discordant twin design is indeed a powerful tool for epigenetic association studies.

Availability and implementation

Computer scripts are available at https://github.com/zickyls/EWAS-Twin-Simulation.

Supplementary information

Supplementary data are available at Bioinformatics online.

Familial aggregation of myocardial infarction and coaggregation of myocardial infarction and autoimmune disease: a nationwide population-based cross-sectional study in Taiwan

OBJECTIVE

This study examined how a history of myocardial infarction (MI) in a person's first-degree relatives affects that person's risk of developing MI and autoimmune diseases.

DESIGN

Nationwide population-based cross-sectional study SETTING: All healthcare facilities in Taiwan.

PARTICIPANTS

A total of 24 361 345 individuals were enrolled.

METHODS

Using data from the National Health Insurance Research Database in Taiwan, we conducted a nationwide cross-sectional study of data collected from all beneficiaries in the Taiwan National Health Insurance system in 2015, of whom 259 360 subjects had at least one first-degree relative affected by MI in 2015. We estimated the absolute risks and relative risks (RRs) of MI and autoimmune disease in those subjects, and the relative contribution of genetic and environmental factors to their MI susceptibility.

RESULTS

The absolute risks of MI for subjects with at least one affected first-degree relative and the general population were 0.87% and 0.56%, respectively, in 2015. Patients with affected first-degree relatives were significantly associated with a higher RR of MI (1.76, 95% CI: 1.68 to 1.85) compared with the general population. There was no association with a higher RR of autoimmune disease. The sibling, offspring and parental MI history conferred RRs (95% CI) for MI of 2.35 (1.96 to 2.83), 2.21 (2.05 to 2.39) and 1.60 (1.52 to 1.68), respectively. The contributions of heritability, shared environmental factors and non-shared environmental factors to MI susceptibility were 19.6%, 3.4% and 77.0%, respectively.

CONCLUSIONS

Individuals who have first-degree relatives with a history of MI have a higher risk of developing MI than the general population. Non-shared environmental factors contributed more significantly to MI susceptibility than did heritability and shared environmental factors. A family history of MI was not associated with an increased risk of autoimmune disease.

Donor cell leukemia

Minimal residual disease refers to the tumour cells that are still present in a given patient after completion of a therapeutic scheme. The demonstration and quantification of residual neoplastic cells has a crucial impact in clinical decision making, for it might prompt continuation of treatment, while the absence of such cells might serve as evidence to withdraw therapy. Therefore, both sensitivity and specificity of the methods used to unravel residual neoplastic cells must be highly reliable and robust. Flow cytometry has been widely used for this purpose, and its clinical performance depends mainly on the criteria of interpretation, rather than in the technique by itself; molecular biology techniques have proved to be highly sensitive and specific but unfortunately they cannot be used in all patients or in all types of leukemia. Finally, the development of donor cell leukemia in transplanted patients, might mimic residual disease and add more confusion to an already controversial issue. These topics are discussed in this paper.

Donor cell leukemia: a critical review

Approximately 40 cases of DCL have been reported in the literature; cases have been reported after allografts from bone marrow, peripheral blood and cord blood. The study of these cases may provide new insights into the mechanisms of leukemogenesis. Some data suggest that the prevalence of this complication has been under-estimated. Most cases of DCL have occurred following transplantation for leukemia, but there have also been cases reported after transplantation for non-malignant conditions. Various mechanisms have been proposed to explain how DCL arise and are briefly discussed. Additional studies are needed to define with more detail both the true prevalence of this complication and its precise pathogenetic mechanism.