AAV prevalence high among Indigenous peoples of Alaska: Study
Native Alaskans, American Indians among most affected groups worldwide
The frequency of ANCA-associated vasculitis (AAV) among the Indigenous peoples of Alaska is high compared with other populations worldwide, especially the granulomatosis with polyangiitis (GPA) form of the disease, a study reports.
Native Alaskans and American Indians in Alaska with AAV also may have more severe clinical features at younger ages, the research, considered to be the first of its kind, suggests.
These findings indicate that “studies of vasculitis in other Indigenous populations are warranted,” the researchers wrote in the study “Prevalence and clinical characteristics of vasculitis in the Alaska Native and American Indian peoples of Alaska,” which was published in Arthritis Care & Research.
A prevalence of vasculitis in any form of 752 per 1 million adults
Vasculitis is a group of diseases marked by blood vessel inflammation. While certain infections or medications cause some forms of vasculitis, most — including AAV — are associated with autoimmune conditions.
Most commonly, AAV is caused by self-reactive antibodies, called ANCAs, that bind to enzymes in a type of immune cell called neutrophils. This ultimately triggers an immune reaction against the cells lining small blood vessels, frequently those in the kidneys and lungs, affecting their function.
Studies investigating the prevalence — the number of established cases — and manifestations of vasculitis in different populations and geographical regions have found significant differences. Still, most reports in the U.S. have focused on areas with predominantly white populations.
Scientists at the Alaska Native Tribal Health Consortium examined the prevalence and clinical manifestations of the many types of vasculitis among Native Alaskans and American Indians there.
“To our knowledge, this study is the first to report the prevalence of many subtypes of vasculitis in a population of Indigenous North American peoples,” the scientists wrote.
They collected electronic health records of participating organizations within the Alaska Tribal Health System to identify adults with a potential vasculitis diagnosis from January 2012 through December 2019.
In total, 74 adults with a validated diagnosis of vasculitis were selected and included in the analysis of clinical characteristics, while the 63 adults still being followed at the end of 2019 were included in the prevalence analysis.
The age-adjusted prevalence per 1 million adults was 752 for all forms of vasculitis, 518 for primary systemic (bodywide) vasculitis, 189 for leukocytoclastic vasculitis limited to the skin, and 44 for drug-associated vasculitis. Leukocytoclastic vasculitis is another type of neutrophil-associated vasculitis that affects small blood vessels.
Among the different forms of primary systemic vasculitis, AAV was the most common, with an age-adjusted prevalence of 340 per 1 million adults.
“Our data suggest that the prevalence of AAV in the AN/AI [Alaska Native and American Indian] peoples of Alaska is higher than most populations and similar to Olmsted County, which previously reported the highest prevalence in the world,” the researchers wrote. That Michigan county reported an AAV prevalence of 421 per 1 million adults in January 2015, a time when the disease’s global pooled prevalence was estimated to be 198 per 1 million persons, they added.
Regarding AAV types, the prevalence among Indigenous adults in Alaska was 244 per 1 million adults for GPA, 86 for microscopic polyangiitis (MPA), and 11 for eosinophilic granulomatosis with polyangiitis (EGPA).
“We report the highest estimated prevalence of GPA in the world in AN/AI adults,” the scientists wrote.
Blood levels of inflammatory markers high at AAV diagnosis
More than half (57%) of those with AAV (excluding EGPA) were women, with no significant difference between GPA and MPA. Mean age at diagnosis was 52.2 for GPA patients (3.9 years younger than the mean age of GPA patients in Olmsted County) and 59.7 years for MPA patients (mean of eight years earlier than Olmsted County).
The most common AAV treatment was systemic corticosteroids, administered to all AAV patients at some point in the disease course. This was followed by rituximab (72% of GPA patients and 40% of MPA patients) and cyclophosphamide (52% of GPA patients and 70% of MPA patients).
In both GPA and MPA, blood tests at diagnosis revealed high levels of inflammatory markers, including the erythrocyte sedimentation rate and the C-reactive protein.
Kidney involvement also was frequent, as indicated by abnormal results on urine tests in more than 78% of patients. Blood creatinine levels suggestive of impaired kidney function were detected in 52% of GPA patients and 90% of MPA patients.
Most GPA patients (72%) tested positive for ANCAs against the proteinase-3 enzyme, while nearly all MPA patients (90%) tested positive for ANCAs against the myeloperoxidase enzyme. These enzymes are the most common targets of ANCAs.
The most commonly affected organs and systems in 25 evaluable GPA patients were the ear, nose, and throat (80%), kidney (80%), and respiratory system (72%). In 10 MPA patients with available data, the kidneys were most frequently affected (90%), followed by the respiratory system (50%).
Nervous system manifestations were less common, occurring in 32% of GPA patients and 40% of MPA patients.
“While this study will help clinicians within the [Alaska Native Tribal Health Consortium] to practice more informed care of AN/AI peoples with vasculitis, more research is needed to identify and address reasons for health disparities, risk and protective factors for developing vasculitis, and clinically relevant differences in clinical manifestations,” the scientists concluded.
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