Arctic Variant Research Articles

The CPT1A Arctic variant: perspectives of community members and providers in two Alaska tribal health settings.

Newborn screening in Alaska includes screening for carnitine palmitoyltransferase 1A (CPT1A) deficiency. The CPT1A Arctic variant is a variant highly prevalent among Indigenous peoples in the Arctic. In this study, we sought to elicit Alaska Native (AN) community member and AN-serving healthcare providers' knowledge and perspectives on the CPT1A Arctic variant. Focus groups with community members and healthcare providers were held in two regions of Alaska between October 2018 and January 2019. Thematic analysis was used to identify recurring constructs. Knowledge and understanding about the CPT1A Arctic variant and its health impact varied, and participants were interested in learning more about it. Additional education for healthcare professionals was recommended to improve providers' ability to communicate with family caregivers about the Arctic variant. Engagement with AN community members identified opportunities to improve educational outreach via multiple modalities for providers and caregivers on the Arctic variant, which could help to increase culturally relevant guidance and avoid stigmatization, undue worry, and unnecessary intervention. Education and guidance on the care of infants and children homozygous for the CPT1A Arctic variant could improve care and reduce negative psychosocial effects.

Genotype-phenotype correlations in CPT1A deficiency detected by newborn screening in Pacific populations.

Carnitine palmitoyltransferase 1A (CPT1A) deficiency is a long chain fatty acid oxidation disorder, typically presenting with hypoketotic hypoglycaemia and liver dysfunction during fasting and intercurrent illness. Classical CPT1A deficiency is a rare disease, although a milder ‘Arctic variant' (p.P479L) is common in the Inuit population. Since the introduction of expanded metabolic screening (EMS), the newborn screening programmes of Hawai'i and New Zealand (NZ) have detected a significant increase in the incidence of CPT1A deficiency. We report 22 individuals of Micronesian descent (12 in NZ and 10 in Hawai'i), homozygous for a CPT1A c.100T>C (p.S34P) variant detected by EMS or ascertained following diagnosis of a family member. No individuals with the Micronesian variant presented clinically with metabolic decompensation prior to diagnosis or during follow‐up. Three asymptomatic homozygous adults were detected following the diagnosis of their children by EMS. CPT1A activity in cultured skin fibroblasts showed residual enzyme activity of 26% of normal controls. Secondly, we report three individuals from two unrelated Niuean families who presented clinically with symptoms of classic CPT1A deficiency, prior to the introduction of EMS. All were found to be homozygous for a CPT1A c.2122A>C (p.S708R) variant. CPT1A activity in fibroblasts of all three individuals was severely reduced at 4% of normal controls. Migration pressure, in part due to climate change may lead to increased frequency of presentation of Pacific peoples to regional metabolic services around the world. Knowledge of genotype–phenotype correlations in these populations will therefore inform counselling and treatment of those detected by newborn screening.

Carnitine Palmitoyl Transferase, Type 1A (CPT1A)

Carnitine Palmitoyl Transferase 1A (CPT1A) is a crucial enzyme needed for mitochondrial fatty acid oxidation and is fundamental for appropriate metabolic responses to prolonged fasting. Under normal conditions, the human body guarantees a constant energy supply, by metabolizing glucose in the short term and by oxidizing fatty acids into ketones during long term fasting or starvation. Fasting induces breakdown of the hepatic glycogen supply into glucose. Continued fasting eventually leads to glycogen depletion followed by a decrease in serum glucose and insulin levels, this decrease then activates hormone-sensitive lipases located in adipose tissues and causes the release of free fatty acids into the blood. Normally these free fatty acids would undergo beta-oxidation to produce energy, but CPT1A deficiency results in an 80% decrease in the activity of the CPT1A enzyme, leading to significant hepatic glycogen depletion and the inability to utilize ketones during periods of fasting. Preoperative fasting in these patients may result in vomiting, lethargy, hypoketotic hypoglycemia, seizures, liver failure, increased risk for infectious illnesses and higher rates of respiratory illnesses, placing this population at greater perioperative risk for anesthesia and surgery. Interventions include, but are not limited to, parent education and prevention techniques, recognition of symptoms, prompt treatment with glucose and even surgery cancellation. CPT1A deficiency is found in circum-arctic populations such as Alaskan Inupiat and Yupik, Canadian and Greenland Inuit, and Siberian Yupik and is thus known as the “Arctic Variant” of CPT1A. Once thought of as a rare disorder, the introduction of tandem mass spectrometry (MS/MS) to Alaska newborn screenings in 2003 revealed that the polymorphism c.1436C>T variant in the CPT1A gene has an incidence as high as 80% in specific regions of Alaska. As of 2011, an estimated 700 Alaska Native Infants born each year are homozygous for the c.1436C>T Arctic Variant. It is therefore important for anesthesia professionals in Alaska and other arctic regions to understand what CPT1A Arctic Variant is, and its implications for these patients in the perioperative period.

Evidence for an association between infant mortality and homozygosity for the arctic variant of carnitine palmitoyltransferase 1A.

PURPOSEInfant mortality in Alaska is highest among Alaska Native people from Western/Northern Alaska, a population with a high prevalence of a genetic variant (c.1436C>T; The Arctic Variant) of carnitine palmitoyltransferase 1A (CPT1A).METHODSWe performed an unmatched case-control study to determine the relationship between the arctic variant and infant mortality. Cases were 110 Alaska Native infant deaths from 2006 to 2010 and controls were 395 Alaska Native births from the same time period. In addition to the overall analysis we conducted two sub-analyses, one limited to subjects from Western/Northern Alaska, and one limited to infants heterozygous or homozygous for the arctic variant.RESULTSAmong Western/Northern Alaska residents, 66% of cases and 61% of controls were homozygous (adjusted odds ratio [aOR] 2.5; 95% confidence interval, 1.3, 5.0). Among homozygous or heterozygous infants, 58% of cases and 44% of controls were homozygous (aOR, 2.3; 95% CI, 1.3, 4.0). Deaths associated with infection were more likely to be homozygous (OR, 2.9; 95% CI, 1.0 to 8.0). Homozygosity was strongly associated with a pre-morbid history of pneumonia, sepsis, or meningitis.CONCLUSIONHomozygosity for the arctic variant is associated with increased risk of infant mortality, which may be mediated in part by an increase in infectious disease risk. Further studies will be needed to determine if the association we report represents a causal association between the CPT1A arctic variant and overall, and infectious disease specific mortality.

Distribution of the arctic variant of the CPT1A gene in indigenous populations of Siberia

Population screening of the Arctic variant, which has arisen due to the G > A mutation at locus rs80356779 in the CPT1A gene, has been performed for the first time among indigenous peoples of Siberia (Chukchi, Koryaks, Evens, Evenks, Yakuts, Buryats and Altaians) and East Asia (Koreans). It is assumed that CPT1A Arctic variant originated from Eskimo ancestors, probably as a result of adaptation to a high-fat diet and/or to the extremely cold environment. It is also known that the homozygous Arctic variant is associated with hypoketotic hypoglycemia attributable to CPT1A deficiency and high infant mortality and occurs at high frequency in American Eskimo. On the other hand, the association of CPT1A Arctic variant with increased levels of HDL-cholesterol and apolipoprotein A1 in blood plasma suggests that this mutation might have a cardioprotective role. In the present study, a high frequency of CPT1A Arctic variant has been found in coastal populations of Northeast Asia – in Koryaks (66 %), Chukchi (56 %) and Evens (30 %), and singularly (at a frequency of 1 %) in Evenks of Central Siberia. Five polymorphic loci relevant to the haplotypic structure of CPT1A gene (rs2278908, rs2278907, rs2924699, rs7112615 and rs2229738) were revealed by high-throughput DNA sequencing in addition to locus rs80356779 studied here. It was found that the Arctic variant haplotype has arisen only once on the basis of the haplotype, which is widespread in modern populations of Eurasia. We assume that the expansion of Eskimo culture of the sea mammal hunting as well as Eskimo assimilation by Chukchi and Koryaks have contributed to the spread of the CPT1A Arctic variant across the populations of indigenous peoples of Northeast Asia.

The Arctic mutation accelerates Aβ aggregation in SDS through reducing the helical propensity of residues 15–25

Mutations within the β-amyloid peptide (Aβ) sequence that cause early onset familial Alzheimer’s disease (FAD) have been shown to promote Aβ aggregation. How these FAD-related mutants increase the aggregative ability of Aβ is not fully understood. Here, we characterized the effect of the Arctic variant (E22G) on the conformational stability of Aβ using various forms of spectroscopy and kinetic analyses, including nuclear magnetic resonance (NMR), circular dichroism (CD) spectroscopy, Fourier-transform infrared (FT-IR) spectroscopy and transmission electron microscopy (TEM). The E22G mutation in the Arctic variant reduced the α-helical propensity and conformational stability of Aβ on residues 15–25. This mutation also caused an increase in both α-helix-to-β-strand conversion and fibril nucleation rates. Our results suggest that the α-helical propensity of residues 15–25 may play a determinant role in the aggregative ability of Aβ. This may provide a structural basis for understanding the molecular mechanism of Aβ aggregation.

Oligomer-targeting with a conformational antibody fragment promotes toxicity in Aβ-expressing flies.

IntroductionThe self-assembly of Aβ peptides into a range of conformationally heterogeneous amyloid states represents a fundamental event in Alzheimer’s disease. Within these structures oligomeric intermediates are considered to be particularly pathogenic. To test this hypothesis we have used a conformational targeting approach where particular conformational states, such as oligomers or fibrils, are recognized in vivo by state-specific antibody fragments.ResultsWe show that oligomer targeting with the KW1 antibody fragment, but not fibril targeting with the B10 antibody fragment, affects toxicity in Aβ-expressing Drosophila melanogaster. The effect of KW1 is observed to occur selectively with flies expressing Aβ(1–40) and not with those expressing Aβ(1–42) or the arctic variant of Aβ(1–42) This finding is consistent with the binding preference of KW1 for Aβ(1–40) oligomers that has been established in vitro. Strikingly, and in contrast to the previously demonstrated in vitro ability of this antibody fragment to block oligomeric toxicity in long-term potentiation measurements, KW1 promotes toxicity in the flies rather than preventing it. This result shows the crucial importance of the environment in determining the influence of antibody binding on the nature and consequences of the protein misfolding and aggregation.ConclusionsWhile our data support to the pathological relevance of oligomers, they highlight the issues to be addressed when developing inhibitory strategies that aim to neutralize these states by means of antagonistic binding agents.

Association of a Genetic Variant of Carnitine Palmitoyltransferase 1A with Infections in Alaska Native Children

To evaluate whether the arctic variant (c.1436C→T) of carnitine palmitoyltransferase type 1A (CPT1A) is associated with a higher incidence of adverse health outcomes in Alaska Native infants and children. We evaluated health measures from birth certificates (n = 605) and Alaska Medicaid billing claims (n = 427) collected from birth to 2.5 years of age for a cohort of Alaska Native infants with known CPT1A genotype. To account for geographic variations in gene distribution and other variables, data also were evaluated in cohorts. When analysis was restricted to residents of nonhub communities in Western and Northern Alaska, children homozygous for the arctic variant experienced more episodes of lower respiratory tract infection than did heterozygous or noncarrier children (5.5 vs 3.7, P = .067) and were more likely to have had otitis media (86% vs 69%, 95% CI 1.4-8.9). Associations were weaker for more homogeneous cohorts. The association of the arctic variant of CPT1A with infectious disease outcomes in children between birth and 2.5 years of age suggests that this variant may play a role in the historically high incidence of these health outcomes among indigenous Arctic populations; further studies will need to assess if this association was confounded by other risk factors.

High-Density Baiting with ONRAB® Rabies Vaccine Baits to Control Arctic-Variant Rabies in Striped Skunks in Ontario, Canada

The Arctic variant of rabies virus has been maintained in striped skunks in small foci in southwestern Ontario, Canada, despite the control of the disease in red foxes. To control the disease in skunks, high-density baiting with ONRAB(®) oral rabies vaccine baits was conducted by air and by hand distribution of baits in the vicinity of skunk cases. During 2009, antibody prevalences in skunks were higher in areas baited at a density of 300 baits/km(2) and flight-line spacing of 0.25 km than at 0.5-km spacing. Once an area containing Arctic-variant cases was treated with high densities of ONRAB baits, the disease did not reoccur in skunks in those areas. During 2009, only eight skunks were diagnosed with the Arctic variant of rabies virus in Ontario.

Influence of Residue 22 on the Folding, Aggregation Profile, and Toxicity of the Alzheimer's Amyloid β Peptide

Several biophysical techniques have been used to determine differences in the aggregation profile (i.e., the secondary structure, aggregation propensity, dynamics, and morphology of amyloid structures) and the effects on cell viability of three variants of the amyloid β peptide involved in Alzheimer's disease. We focused our study on the Glu22 residue, comparing the effects of freshly prepared samples and samples aged for at least 20 days. In the aged samples, a high propensity for aggregation and β-sheet secondary structure appears when residue 22 is capable of establishing polar (Glu22 in wild-type) or hydrophobic (Val22 in E22V) interactions. The Arctic variant (E22G) presents a mixture of mostly disordered and α-helix structures (with low β-sheet contribution). Analysis of transmission electron micrographs and atomic force microscopy images of the peptide variants after aging showed significant quantitative and qualitative differences in the morphology of the formed aggregates. The effect on human neuroblastoma cells of these Aβ12–28 variants does not correlate with the amount of β-sheet of the aggregates. In samples allowed to age, the native sequence was found to have an insignificant effect on cell viability, whereas the Arctic variant (E22G), the E22V variant, and the slightly-aggregating control (F19G-F20G) had more prominent effects.

Recombinant amyloid beta-peptide production by coexpression with an affibody ligand

BackgroundOligomeric and fibrillar aggregates of the amyloid β-peptide (Aβ) have been implicated in the pathogenesis of Alzheimer's disease (AD). The characterization of Aβ assemblies is essential for the elucidation of the mechanisms of Aβ neurotoxicity, but requires large quantities of pure peptide. Here we describe a novel approach to the recombinant production of Aβ. The method is based on the coexpression of the affibody protein ZAβ3, a selected affinity ligand derived from the Z domain three-helix bundle scaffold. ZAβ3 binds to the amyloidogenic central and C-terminal part of Aβ with nanomolar affinity and consequently inhibits aggregation.ResultsCoexpression of ZAβ3 affords the overexpression of both major Aβ isoforms, Aβ(1–40) and Aβ(1–42), yielding 4 or 3 mg, respectively, of pure 15N-labeled peptide per liter of culture. The method does not rely on a protein-fusion or -tag and thus does not require a cleavage reaction. The purified peptides were characterized by NMR, circular dichroism, SDS-PAGE and size exclusion chromatography, and their aggregation propensities were assessed by thioflavin T fluorescence and electron microscopy. The data coincide with those reported previously for monomeric, largely unstructured Aβ. ZAβ3 coexpression moreover permits the recombinant production of Aβ(1–42) carrying the Arctic (E22G) mutation, which causes early onset familial AD. Aβ(1–42)E22G is obtained in predominantly monomeric form and suitable, e.g., for NMR studies.ConclusionThe coexpression of an engineered aggregation-inhibiting binding protein offers a novel route to the recombinant production of amyloidogenic Aβ peptides that can be advantageously employed to study the molecular basis of AD. The presented expression system is the first for which expression and purification of the aggregation-prone Arctic variant (E22G) of Aβ(1–42) is reported.

A preliminary archaeological survey of a Tupolev TB-3 (ANT-6) aircraft on Ostrov Rudol'fa, Zemlya Frantsa-Iosifa, Russia

The partially snow-covered wreck of specially-modified Arctic variant of the Tupolev TB-3 four-engine bomber was located at Buhkta Teplits [Teplits Bay], Ostrov Rudol'fa [Rudolf Island] in Zemlya Frantsa-Iosifa [Franz Josef Land]. From data gathered, the wreck was subsequently identified as TB-3 (ANT-6) No. 210. This aircraft was piloted by Boris Chukhnovsky during a failed search for another TB-3 (ANT-6), No. 209, which had been lost in August 1937 during an attempt to fly from Moscow over the north pole to the United States. The Teplits TB-3 (ANT-6) wreck represents both the primary aeronautical archaeology of the triumphs and disasters of the Soviet Union's air expeditions to the pole in 1937–1938 and, at 81°47.5'N, is the northernmost aircraft wreck yet identified.

Elimination of Arctic Variant Rabies in Red Foxes, Metropolitan Toronto

To control the arctic variant of rabies virus in red foxes, 332,257 bait doses containing live, attenuated Evelyn-Rokitnicki-Abelseth rabies vaccine were distributed in greater metropolitan Toronto during 1989–1999. Human and pet contact with bait was minimal, and no adverse reactions to the vaccine were noted. Significantly fewer rabid foxes were found during the 17 years after fox baiting (5 cases during 1990–2006) than in the 17 years before (96 cases during 1973–1989). The last report of a rabid fox in metropolitan Toronto was in 1996 (reporting period through September 2006), which confirms that distributing oral rabies vaccine bait is a feasible tactic for the control of rabies in foxes in urban environments.

Abeta protofibrils possess a stable core structure resistant to hydrogen exchange.

Protofibrils are transient structures observed during in vitro formation of mature amyloid fibrils and have been implicated as the toxic species responsible for cell dysfunction and neuronal loss in Alzheimer's disease (AD) and other protein aggregation diseases. To better understand the roles of protofibrils in amyloid assembly and Alzheimer's disease, we characterized secondary structural features of these heterogeneous and metastable assembly intermediates. We chromatographically isolated different size populations of protofibrils from amyloid assembly reactions of Abeta(1-40), both wild type and the Arctic variant associated with early onset familial AD, and exposed them to hydrogen-deuterium exchange analysis monitored by mass spectrometry (HX-MS). We show that HX-MS can distinguish among unstructured monomer, protofibrils, and fibrils by their different protection patterns. We find that about 40% of the backbone amide hydrogens of Abeta protofibrils are highly resistant to exchange with deuterium even after 2 days of incubation in aqueous deuterated buffer, implying a very stable, presumably H-bonded, core structure. This is in contrast to mature amyloid fibrils, whose equally stable structure protects about 60% of the backbone amide hydrogens over the same time frame. We also find a surprising degree of specificity in amyloid assembly, in that wild type Abeta is preferentially excluded from both protofibrils and fibrils grown from an equimolar mixture of wild type and Arctic mutant peptides. These and other data are interpreted and discussed in terms of the role of protofibrils in fibril assembly and in disease.

Mixtures of Wild-type and a Pathogenic (E22G) Form of Aβ40 in Vitro Accumulate Protofibrils, Including Amyloid Pores

Although APP mutations associated with inherited forms of Alzheimer's disease (AD) are relatively rare, detailed studies of these mutations may prove critical for gaining important insights into the mechanism(s) and etiology of AD. Here, we present a detailed biophysical characterization of the structural properties of protofibrils formed by the Arctic variant (E22G) of amyloid-β protein (Aβ40 ARC) as well as the effect of Aβ40 WT on the distribution of the protofibrillar species formed by Aβ40 ARC by characterizing biologically relevant mixtures of both proteins that may mimic the situation in the heterozygous patients. These studies revealed that the Arctic mutation accelerates both Aβ oligomerization and fibrillogenesis in vitro. In addition, Aβ40 ARC was observed to affect both the morphology and the size distribution of Aβ protofibrils. Electron microscopy examination of the protofibrils formed by Aβ40 ARC revealed several morphologies, including: (1) relatively compact spherical particles roughly 4–5 nm in diameter; (2) annular pore-like protofibrils; (3) large spherical particles 18–25 nm in diameter; and (4) short filaments with chain-like morphology. Conversion of Aβ40 ARC protofibrils to fibrils occurred more rapidly than protofibrils formed in mixed solutions of Aβ40 WT/Aβ40 ARC, suggesting that co-incubation of Aβ40 ARC with Aβ40 WT leads to kinetic stabilization of Aβ40 ARC protofibrils. An increase in the ratio of Aβ WT/Aβ MUT(Arctic), therefore, may result in the accumulation of potential neurotoxic protofibrils and acceleration of disease progression in familial Alzheimer's disease mutation carriers.