The genetics of multiple sclerosis

Lifestyle factors and multiple sclerosis: A population-based incident case-control study

OBJECTIVE

Although low sun exposure, low vitamin D, and smoking are established risk factor of multiple sclerosis (MS), there is less evidence on the role of the other lifestyle factors. We examined the association of sun exposure, physical activity, drug abuse, and alcohol intake with MS.

MATERIALS AND METHODS

This was population-based incident case-control study in Iran with 547 incident cases and 1057 general population controls (7/8/2013-17/2/2015). Logistic regression was used to analyse the data.

RESULTS

Higher sun exposure during adolescence was associated with a reduced risk of MS, both in summer (test for trend p < 0.001) and winter (P < 0.001), while physical activity was not associated with MS (test for trend p = 0.712). Lifetime drug abuse (OR for ever use 2.93 (1.83-4.70)), with a dose-response association (test for trend p < 0.001), and alcohol intake (OR for ever use 1.49 (1.05-2.12)) was significantly associated with an increased risk of MS.

CONCLUSION

In a middle-eastern setting, we found that sun exposure during adolescence, drug abuse, and alcohol use were all associated with MS. Increasing sun exposure and reducing drug abuse and the use of alcohol through educational programs is likely to reduce the rate of MS.

Cerebrospinal fluid biomarkers in multiple sclerosis

In patients with multiple sclerosis (MS) intensive efforts are directed at identifying biomarkers in bodily fluids related to underlying disease mechanisms, disease activity and progression, and therapeutic response. Besides MR imaging parameters cerebrospinal fluid (CSF) biomarkers provide important and specific information since changes in the CSF composition may reflect disease mechanisms inherent to MS. The different cellular and protein-analytical methods of the CSF and the recommended standard of the diagnostic CSF profile in MS are described. A brief update on possible CSF biomarkers that might reflect key pathological processes of MS such as inflammation, demyelination, neuroaxonal loss, gliosis and regeneration is provided.

Presence of Epstein-Barr virus and human herpesvirus 6B DNA in multiple sclerosis patients: associations with disease activity

OBJECTIVE

To assess the presence of Epstein-Barr virus (EBV) and human herpesvirus 6B (HHV-6B) DNA in saliva and plasma from multiple sclerosis (MS) patients enrolled in a randomized, double-blind, placebo-controlled valacyclovir treatment study.

METHODS

DNA was prepared following ultracentrifugation of saliva and plasma. EBV and HHV-6B DNAs were determined by real-time polymerase chain reaction.

RESULTS

EBV and HHV-6B DNAs were detected in 41% and 65% of saliva samples, respectively. In patients treated with valacyclovir, the percentage of saliva samples with EBV was significantly reduced (9%; P = 0.000017), whereas the frequency of HHV-6B positive samples was unchanged (57%; P = 0.38). Longitudinal studies demonstrated a time-dependent reduction in the frequency of saliva samples containing EBV following valacyclovir treatment. In contrast, plasma contained EBV and HHV-6B DNAs in 17% and 25% of the samples, respectively, and these numbers were not significantly reduced following valacylovir treatment (13% and 16%, respectively), nor were they different from those of healthy controls (6% and 39%, respectively). Patients with high disease activity had a significantly higher frequency of EBV (P = 0.018) and HHV-6B (P = 0.023) positive samples than did patients with low disease activity. The presence of EBV and HHV-6B was strongly correlated in plasma (P < 0.00000001), but not in saliva (P = 0.41).

CONCLUSION

MS patients express EBV and HHV-6B in both saliva and plasma, but only the expression of EBV in saliva is significantly reduced following valacyclovir treatment. Although EBV and HHV-6B DNAs can be detected in plasma from healthy individuals, the co-expression of both these viruses in MS patients is highly significant and further associated with clinical activity. The observations of viral DNA in plasma are consistent with an underlying immunologic defect in MS.

Genetic linkage and association studies in bipolar affective disorder: a time for optimism

Genetic research on complex diseases is beginning to bear fruit, with the successful identification of candidate susceptibility genes in diabetes, asthma, and other illnesses. Similar success is on the horizon for bipolar affective disorder (BPAD), but significant challenges remain. In this review, we outline the basic concepts of linkage and association mapping for complex phenotypes. We point out important caveats inherent in both approaches, and review guidelines on the interpretation of linkage statistics and significance thresholds. We then apply these concepts to an evaluation of the present status of genetic linkage and association studies in BPAD. The challenges posed by locus heterogeneity, phenotype definition, and sample size requirements are given a detailed treatment. Despite these challenges, we argue that the way ahead remains firmly rooted in linkage studies, complemented by association studies in linked regions. This is the only truly genome-wide approach currently available; it has succeeded in other complex phenotypes, and it is the surest strategy for mapping susceptibility genes in BPAD. Once these genes are identified, genetic mapping methods will yield to the other methods of 21st-century molecular biology as we begin to elucidate the pathophysiology of BPAD.

Detection of infectious agents in brain of patients with acute hemorrhagic leukoencephalitis

Acute hemorrhagic leukoencephalitis (AHL) is a rare and usually fatal disorder characterized clinically by an acute onset of neurologic abnormalities. It may occur in association with a viral illness or vaccination. Radiology and brain biopsy are essential for the diagnosis. The etiology of AHL is unclear. We postulated that viral/bacterial infection might be responsible, directly or through an immune-mediated mechanism, for this acute inflammatory myelinopathy. Fifteen cases of AHL were studied. Infectious agents, including varicella zoster virus (VZV), herpes simplex virus (HSV), human herpes virus-6 (HHV-6), cytomegalovirus, Epstein-Barr virus, and Mycoplasma, were investigated in brain specimens using the polymerase chain reaction (PCR), reverse transcriptase (RT)-PCR, and immunohistochemistry. Using PCR, HSV DNA was found in four cases, VZV DNA in two, and HHV-6 DNA in one. Among the control cases, two were HSV DNA positive. Further investigation to detect HSV RNA and antigens in HSV DNA-positive cases revealed that two cases with AHL were both HSV RNA and antigen positive. AHL is a hyperacute disease, which is considered the most acute form of acute disseminated encephalomyelitis (ADEM). Our findings suggests that a viral infection may be implicated in its pathogenesis, most likely through an indirect mechanism; however, as only a few cases of this rare disease were examined, statistical significance was not achieved. As a number of patients with disorders of the ADEM group may progress to develop multiple sclerosis (MS), we argue that an organism that has produced the former may remain in the brain tissue and be subsequently involved in the production of a self-sustained disorder such as MS.

Identification of susceptibility genes for experimental autoimmune encephalomyelitis that overcome the effect of protective alleles at the eae2 locus

We have previously identified a locus on mouse chromosome 15 (eae2) that regulates susceptibility to experimental autoimmune encephalomyelitis in a cross between the susceptible strain B10.RIII and the resistant strain RIIIS/J. In an effort to verify the protective effect from having two RIIIS/J alleles at eae2, the resistant locus was bred into the susceptible strain in homozygous form. However, the expected effect was not as clear as in the original study. This might be due to an epistatic effect conferred by several unidentified genes in the genome of the resistant strain or due to the environment by genotype interactions, possibly overcoming the effect of protective alleles at eae2. To further the genetic understanding in this disease, a genome-wide linkage screening approach was employed on an F(2) intercross that carried the protective allele at eae2in homozygous form while the rest of the genome segregated between the B10.RIII and RIIIS/J strains as in the original investigation. In the present study we find one region on chromosome 7, not previously identified in this strain combination, that affects the disease at significant logarithm of the odds score and six regions showing suggestive evidence for linkage to disease phenotypes.