Use of Dried Blood Spots to Study the Arctic Variant of CPT1A. David M. Koeller, MD Oregon Health & Science University

Transcription

1 Use of Dried Blood Spots to Study the Arctic Variant of CPT1A David M. Koeller, MD Oregon Health & Science University

2 Objectives: The CPT1A Arctic Variant in Alaska Discovery and Prevalence Metabolic Impact Clinical Consequences The Future Newborn screening Long Term Follow Up Genetic Epidemiology

3 Fall 2003: Alaska Begins Expanded Screening by MS/MS

4 Infants screen positive for CPT1A deficiency First seven confirmed by enzyme assay in cultured fibroblasts (Dr. Michael Bennett, University of Pennsylvania) Relatively high residual activity in cultured fibroblasts (19%) Confirmation by DNA analysis All homozygous for c.1436c T (p.p479l) c.1436c T = The Arctic Variant

5 Infants screened positive for CPT1A deficiency All affected infants were Alaska Natives All were homozygous for the arctic variant Incidence: 1/130 Alaska Native births

6 March 2006 September 2006 Department of Health and Social Services Division of Public Health Editors: Karleen Jackson, Commissioner Richard Mandsager, MD, Director 3601 C Street, Suite 540, PO Box Anchorage, AK Local (907) Hour Emergency (907) Jay C. Butler, MD Joe McLaughlin, MD, MPH Bulletin No. 19 September 13, 2006 Carnitine Palmitoyl Transferase-1A Deficiency Rates in Alaska BACKGROUND According to state statute Sec and regulations 7AAC , all newborn babies in Alaska are required to undergo screening for metabolic disorders. In October 2003, screening was expanded to include more than 30 conditions. Carnitine pal mitoyl transferase-1a (CPT-1A) deficiency, one of the newly added conditions, is a rare, autosomal recessive disease that results in defective fatty acid metabolism. Patients with untreated CPT-1A deficiency usually present for medical care after the newborn period with seizures or c oma associated with life-threatening episodes of fasting hypoketotic hypoglycemia. Treatment of this disorder requires frequent feedin g of affected infants. Other treatment modalities may include a diet low in fat, high in carbohydrates, and supplemented with medium chain triglyceride oils. If treatment is not implemented and repeated episodes of metabolic crisis occur, there is a chance for permanent learning disabilities or mental retardati on. After 5 years of age, metabolic crises tend to happen less frequently and are not as severe. With prompt and careful treatment, children with CPT-1A deficiency often live healthy lives with typical growth and development. October June CPT1A cases identified 1.3 per 1,000 live births CPT-1A deficiency screening tests for Alaska are performed at the Oregon Public Health Laboratory, using tandem mass spectrometry (TMS) analysis of a heel stick blood spot. Positive screening results are reported to the Alaska Division of Public Health (DPH) to facilitate confirmation of diagnosis. The purpose of this Bulletin is to inform health-care providers of the incidence of detected CPT-1A deficiency in Alaska and to provide appropriate follow-up recommendations. RECOMMENDATIONS 1. Refer CPT-1A-deficient patients to the State Metabolic Genetics Clinic for consultation regarding specific dietary guidelines and follow-up evaluation (call during working hours). 2. Consider CPT-1A deficiency in pediatric/adolescent patients-particularly Alaska Natives-who present with hypoketotic hypoglycemia (call the Newborn Metabolic Screening Program at for information). 3. Test biological siblings to newly identified CPT-1Adeficient patients, using the DNA diagn ostic test. 4. Instruct parents of children with CPT-1A deficiency to follow the age-specific feeding guidelines detailed in the Alaska Department of Health and Social Services CPT-1 Deficiency Brochure.4 5. Instruct parents to bring their CPT-1A-deficient infants in for medical evaluation if they have not eaten for >8 hours. 6. If a CPT-1A-deficient infant/child requi res surgery, administer glucose-containing intravenous fluids before surgery and continue until the child is able to eat. 7. For additional information, contact the Section of Women s, Children s & Family Health at All cases in Alaska Natives 63% Western Alaska 21% Northern Alaska METHODS We examined CPT-1A deficiency incidence rates among infants born in Alaska after expansion of the metabolic screening panel. 5.2 per 1,000 live births RESULTS From October 1, 2003 through June 30, 2006, 28,340 births occurred in Alaska and 38 infants with CPT-1A deficiency were reported to DPH (rate, 1.3 per 1,000 live births). All identified cases occurred am ong Alaska Natives (rate, 5.3 per 1,000 live births). Of the 38 infants with CPT-1A deficiency identified, 24 (63%) lived in Western Alaska, 8 (21%) lived in Northern Alaska, a nd 6 (16%) lived in other regions of Alaska. Twenty -five (66%) of the infants were male.

7 August 2007

8 Molecular Genetics and Metabolism 96 (2009) Tested 422 consecutive Inuit births and found an allele frequency of 0.81 for the arctic variant. Found a high frequency among First Nations of Vancouver Island Nunavut

9 Are We Missing Something?

10 Analysis of the sensitivity of MS/MS to detect infants homozygous for the arctic variant 2,500 consecutive newborn screening cards MS/MS and DNA testing Funding Alaska Native Medical Center Alaska Division of Public Health

11 DNA MS/MS Arctic variant = 1436T 2063 homozygous 1436C (83%) 248 heterozygous 1436C/T (10%) 173 homozygous 1436T (7%) 18 positive MS/MS screens none on the first screen 16 on second, 2 on third 173 DNA positive 10,500 births per year in Alaska 735 homozygous infants annually Ascertainment by MS/MS = 10%

12 Prevalence of the Arctic Variant in Alaska Natives All Alaska: 26% homozygous 35% heterozygous Northern and Western Alaska 51% homozygous 47% heterozygous Allele frequency: 0.7 Journal of Pediatrics 2011;158:124-9

13 Metabolism

14 Carnitine Palmitoyltransferase1A (CPT1A) Required for import of long chain fatty acids into the mitochondrion Essential for liver ketone and ATP production from fat Deficiency impairs fasting ketogenesis and gluconeogenesis

15 Does homozygosity for the arctic variant affect ketogenesis? Inpatient fasting study: Five homozygous 3-4 year Alaska Native children All had a severe impairment in ketogenesis Two became hypoglycemic in < 18 hours Molecular Genetics and Metabolism 104 (2011) Funding: Oregon Clinical and Translational Research Institute

16 Is the arctic variant clinically significant?

17 NEW WAINWRIGHT BARROW BEAUFORT SEA POINT LAY BREVIG MISSION POINT HOPE TELLER Legend Geographic Distribution of the Arctic Variant GAMBELL CHUKCHI SEA KOTZBUE SHISHMAREF NOORVIK SELAWIK BUCKLAND KOYUK SAVOONGA NOME NORTON SOUND KOTLIK MOUNTAIN VILLAGE HOOPER BAY PILOT STATION SHUNGAK FAIRBANKS FORT YUKON NORTH POLE Canada Proportion Homozygous Proportion Homozygous or Heterozygous CHEVAK RUSSIAN MISSION NEWTOK WASILLA HOUSTON PALMER NIKISKI ANCHORAGE KENAI Other Village (Untitled) Miles DILLINGHAM BRISTOL BAY STUYAHOK GULF OF ALASKA JUNEAU BERING SEA KODIAK AKIACHAK TULUKSAK SITKA Infant Mortality Rates by Region BETHEL AKIAK KWETHLUK NAPAKIAK NAPASKIAK METLAKATLA KETCHIKAN Region IMR Northern 12.1* Southwest 10.8* Anchorage/Mat- Su 6.3 (ref) Gulf Coast 6.2 The IMR rate in the Inuit is three times the overall rate in Canada Interior 6.2 Southeast 6.2

18 PEDIATRICS 126, Number 5, November 2010 Association of a Genetic Variant of Carnitine Palmitoyltransferase 1A with Infections in Alaska Native Children Bradford D. Gessner, Melanie B. Gillingham, Thalia Wood, David M. Koeller Submitted

19 Hypothesis: Homozygosity for the arctic variant is a risk factor for infant death

20 Impact of the CPT1A Arctic Variant on Infant Mortality in Alaska R03 HD A1 Unmatched case-control study Cases: 110 Alaska Native infant deaths (2006 through 2010) Controls: 395 Alaska Native births from the same time period 80% power to detect an odds ratio of ~ 2.0 with 95% confidence Genotyping done using DNA from newborn screening cards

21 Rates of homozygosity for the arctic variant in cases and controls Cases Controls All subjects 46 of 110 (42%) 119 of 395 (30%) Homozygous and heterozygous Residents of Western and Northern Alaska 46 of 79 (58%) 119 of 269 (44%) 38 of 58 (66%) 112 of 185 (51%)

22 Association between homozygosity and infant mortality All birth weights Odds ratio (95% CI) Adjusted* odds ratio (95% CI) All subjects 1.7 (1.1, 2.6) 1.8 (1.1, 2.9) Homozygous and heterozygous Residents of Western and Northern Alaska 1.8 (1.1, 2.9) 2.3 (1.3, 4.0) 1.8 (0.98, 3.3) 2.5 (1.3, 5.0) * Odds ratio adjusted for maternal education, maternal prenatal alcohol and tobacco use, and a composite variable combining marital status and presence of the father s name on the birth certificate. Normal birth weights Odds ratio (95% CI) Adjusted* odds ratio (95% CI) All subjects 1.7 (1.1, 2.7) 1.8 (1.1, 2.9) Homozygous and heterozygous Residents of Western and Northern Alaska 1.7 (0.99, 2.9) 2.2 (1.2, 3.9) 2.2 (1.1, 4.2) 3.0 (1.4, 6.3)

23 Summary: Homozygosity for the arctic variant of CPT1A is associated with an increased risk of infant mortality and infectious disease outcomes. The risk of infant mortality associated with the variant accounts for the majority of the increased risk observed in Southwestern and Northern Alaska Early identification of homozygous infants and education of parents and local health providers could significantly reduce infant mortality in Alaska Native infants Current MS/MS based newborn screening only ascertains ~ 10% of homozygous infants

24 Where Do We Go From Here?

25 Current Activities Regular meetings with stakeholders Alaska Division of Public Health Alaska Native Tribal Health Consortium Alaska Native Medical Center Presentations in regions of high prevalence ( Barrow, Bethel, Dillingham, Kotzebue, Nome ) Full ascertainment by newborn screening MS/MS combined with DNA testing

26 Results from the MS/MS Sensitivity Study C0 / (C16 + C18)

27 C0 / (C16 + C18) What if we lower the cutoff?

28 To develop a better screening algorithm we have been working with Piero Rinaldo and using the R4S tools

29 Scatter Plot First sample 172 homozygotes 244 heterozygotes Second sample 135 homozygotes 212 heterozygotes

30 Summary FIRST SCREEN SECOND SCREEN Sensitivity 91.12% Specificity 99.18% PPV 89.00% NPV 89.00% FPR 0.76% Sensitivity 84.96% Specificity 96.23% PPV 61.00% NPV 99.00% FPR 3.53%

31 Future Plans Implement a new screening algorithm (MS/MS +DNA) Expand educational efforts (DVD, Health Aide training, etc.) Work with stake holders in Alaska, The Western States Regional Genetics Collaborative, and the NBSTRN to develop a comprehensive long term follow up study Track health outcomes on all Alaska Native infants (2,500/yr) by genotype Assess possible dietary impact on health outcomes Impact of full ascertainment on infant mortality in Alaska Natives Look for unexpected / unbiased impacts of the arctic variant Role of the arctic variant in the high rates of Hib, RSV, and Strep pneumonia in Northern and Western Alaska

32 Acknowledgements OHSU Sue Richards Monique Johnson Melanie Gillingham Cary Harding Bill Lambert NWRNSP Dave Sesser Cheryl Hermerath Mike Skeels Leanne Rein Mayo Clinic Dieter Matern Piero Rinaldo Alaska DHSS Brad Gessner Thalia Wood Stephanie Birch Alaska Native Medical Center Michele Myers Matt Hirschfeld Alaska Native Tribal Health Consortium Jay Butler University of British Columbia Hilary Vallance Graham Sinclair

33 Funding Support Oregon Clinical and Translational Research Institute NICHD Alaska Division of Public Health Alaska Native Medical Center Special Thanks Research Ethics Review Board, Norton Sound Health Corporation The children and families that participated in these studies

34 Questions?