How PKC Gene Variants Shape the Vitamin D–Relapse Relationship in Multiple Sclerosis
Multiple sclerosis is a chronic inflammatory and neurodegenerative disorder of the central nervous system whose development and progression are shaped by interactions between genetic susceptibility and environmental exposure. Among the environmental factors associated with multiple sclerosis, reduced ultraviolet radiation exposure and low circulating vitamin D concentrations have received particular attention. Serum 25-hydroxyvitamin D, abbreviated 25(OH)D, is the principal biomarker used to assess vitamin D status because it reflects both dietary intake and cutaneous synthesis. Previous longitudinal studies have reported an inverse association between 25(OH)D concentrations and relapse risk, suggesting that higher vitamin D status may have a protective role in relapsing–remitting multiple sclerosis. However, this relationship is unlikely to be uniform across all patients. The study by Lin and colleagues investigated whether genetic variation within the vitamin D metabolic and signalling pathways modifies the association between serum 25(OH)D and subsequent relapse. The work is therefore important because it moves beyond examining genes and environmental exposures independently and instead evaluates how inherited variation may alter an individual’s biological response to vitamin D.
Prospective Investigation of a Well-Characterized Patient Cohort
The researchers analysed data from the Southern Tasmanian Multiple Sclerosis Longitudinal Study, a prospective cohort established to examine the effects of ultraviolet radiation and vitamin D on the clinical course of multiple sclerosis. The analysis included 141 participants with relapsing–remitting disease who had both longitudinal clinical information and genotype data. Participants were followed for an average of 2.3 years, during which 122 physician-validated relapses occurred among 70 individuals. Approximately three-quarters of the cohort were women, the mean age was 45.9 years, and more than 82% used immunomodulatory therapy during the study period. Blood samples were collected during summer and winter reviews, and serum 25(OH)D was measured using a radioimmunoassay after follow-up had concluded. This retrospective laboratory analysis ensured that neither participants nor clinical investigators knew the vitamin D results during the observation period, reducing the possibility that knowledge of vitamin D status influenced behaviour, treatment decisions, or relapse reporting. Relapses were assessed using established diagnostic criteria and validated by both the study physician and neurologist.
Pathway-Based Genetic and Statistical Analysis
Rather than conducting an unrestricted genome-wide search, the investigators used a biologically informed pathway approach. They constructed a pathway incorporating vitamin D metabolism and the formation of the vitamin D receptor–retinoid X receptor transcriptional complex. As illustrated in the pathway diagram on page 3 of the article, this network connects enzymes involved in vitamin D activation and degradation with nuclear receptor signalling and members of the protein kinase C family. Twenty-one genes were selected, and 276 single-nucleotide polymorphisms located within or immediately adjacent to these genes were tested. Multilevel mixed-effects regression was used to identify genetic predictors of serum 25(OH)D while accounting for season, age, body mass index, skin melanin density, sun exposure, vitamin D supplementation, fish intake, and smoking. Recurrent relapses were analysed with Cox proportional hazards models using a gap-time formulation. Because vitamin D was measured only during seasonal reviews, the researchers modelled monthly 25(OH)D values using a sinusoidal function representing the expected annual cycle. Interaction terms were then introduced to determine whether the association between modelled vitamin D concentrations and relapse differed according to genotype. Statistical significance was corrected for the 21 genes examined, reducing the likelihood of false-positive findings from multiple testing.
PRKCZ and PRKCH Variants Modified the Vitamin D–Relapse Relationship
The principal finding was that variants in two protein kinase C genes significantly modified the relationship between serum 25(OH)D and relapse. The relevant polymorphisms were rs908742 in PRKCZ and rs3783785 in PRKCH. Both variants are intronic, meaning that they are located within non-coding regions of their respective genes, although intronic variants may still influence transcription, RNA processing, or regulatory activity. Among participants with the major homozygous genotype of rs3783785, higher 25(OH)D was strongly associated with a lower relapse hazard, with a hazard ratio of 0.76 for the vitamin D increment used in the model. In contrast, no significant protective association was detected among carriers of the minor allele. A similar pattern was observed for rs908742. Participants with the major homozygous genotype showed a protective association between vitamin D and relapse, whereas individuals homozygous for the minor allele showed an increased relapse hazard as 25(OH)D rose. Importantly, neither variant was independently associated with vitamin D concentrations or relapse risk. Their relevance emerged specifically through interaction with serum vitamin D, indicating that they may alter the biological consequences of a given 25(OH)D concentration rather than directly determining vitamin D status or relapse susceptibility.
Genetic Determinants of Circulating Vitamin D Concentrations
The study also identified two polymorphisms associated with lower serum 25(OH)D: rs1993116 in CYP2R1 and rs7404928 in PRKCB. CYP2R1 encodes a hepatic vitamin D 25-hydroxylase that contributes to the conversion of vitamin D into 25(OH)D. The association is therefore biologically plausible and consistent with previous genome-wide studies of vitamin D insufficiency. For rs1993116, the researchers observed an allele-dosage relationship. Compared with minor-allele homozygotes, heterozygotes had 25(OH)D concentrations approximately 7.1 nmol/L lower, while major-allele homozygotes had concentrations approximately 12.4 nmol/L lower. The PRKCB variant was associated with a reduction of approximately 7.2 nmol/L in the relevant genotype group. When the two vitamin D–lowering genotypes were combined into a genetic risk score, individuals carrying both had mean 25(OH)D concentrations 13.58 nmol/L lower than those carrying no more than one. Together, these variants accounted for approximately 3.5% of the observed variation in serum vitamin D concentrations, with the CYP2R1 polymorphism explaining most of this proportion. Neither variant significantly modified the relationship between vitamin D and relapse, suggesting that genetic determinants of vitamin D concentration may be distinct from genetic determinants of vitamin D responsiveness.
Protein Kinase C Signalling as a Potential Immunological Mechanism
The concentration of findings within the protein kinase C family provides a plausible mechanistic connection between vitamin D signalling and multiple sclerosis activity. Protein kinase C enzymes regulate intracellular signalling processes involved in T-cell activation, proliferation, migration, and cytokine responses. Because multiple sclerosis relapses are believed to involve aberrant activation and trafficking of autoreactive immune cells into the central nervous system, altered protein kinase C activity could influence the intensity or duration of inflammatory episodes. Vitamin D may intersect with this pathway at several levels. The active metabolite 1,25-dihydroxyvitamin D binds the vitamin D receptor, which forms a transcriptionally active complex with the retinoid X receptor. Protein kinase C can participate in downstream vitamin D signalling and may also phosphorylate the vitamin D receptor, potentially changing its transcriptional activity. Variants in PRKCZ and PRKCH could therefore alter how immune cells respond to vitamin D-mediated signals, while PRKCB variation could influence both vitamin D-related signalling and T-cell migration. The study additionally observed suggestive, although not multiple-testing-corrected, associations between relapse and variants in PRKCE, GC, and RXRA. A cumulative score based on four such variants showed a marked dose–response pattern, with participants carrying four risk genotypes experiencing a relapse hazard more than four times that of the reference group. These results support a network model in which multiple modest genetic effects converge on related immunological pathways.
Clinical Significance, Limitations, and Future Research
The study provides evidence that the clinical relationship between vitamin D and multiple sclerosis relapse may depend partly on genotype. This finding has potential implications for precision medicine because it suggests that identical serum 25(OH)D concentrations may not confer identical biological effects in all patients. Nevertheless, the results should not be interpreted as evidence that vitamin D supplementation should be determined by these variants in current clinical practice. The cohort was relatively small for a genetic interaction study, some genotype groups contained few participants, and several associations with relapse did not remain significant after correction for multiple comparisons. The modelling of monthly vitamin D concentrations also depended on assumptions about seasonal variation between measured time points. Conversely, the prospective design, physician-validated relapses, repeated vitamin D measurements, detailed assessment of environmental confounders, and biologically grounded pathway analysis strengthen the study. The findings are best regarded as hypothesis-generating evidence that protein kinase C signalling may mediate interindividual differences in vitamin D responsiveness. Larger longitudinal cohorts, replication in ethnically diverse populations, functional analyses of the implicated variants, and experimental studies of vitamin D receptor phosphorylation and T-cell signalling will be necessary to establish causality. Ultimately, integrating genetic variation, environmental exposure, and immune-cell function may provide a more accurate account of relapse biology than examining any of these factors in isolation.
Disclaimer: This blog post is based on the provided research article and is intended for informational purposes only. It is not intended to provide medical advice. Please consult with a healthcare professional for any health concerns.
References:
Lin, R., Taylor, B. V., Simpson Jr, S., Charlesworth, J., Ponsonby, A. L., Pittas, F., ... & van der Mei, I. A. (2014). Novel modulating effects of PKC family genes on the relationship between serum vitamin D and relapse in multiple sclerosis. Journal of Neurology, Neurosurgery & Psychiatry, 85(4), 399-404.
