Sugar in the Arctic:

The Arctic Variant of CPT1A and Congenital Sucrase Isomaltase Deficiency

Matthew Hirschfeld, MD/PhDMatthew Hirschfeld, MD/PhD

Maternal Child HealthMaternal Child HealthAlaska Native Medical CenterAlaska Native Medical Center

Anchorage, AKAnchorage, AK

Background•CPT1 = carnitine palmitoyltransferase

type 1

• Expressed in fibroblasts, liver, brain, skin, skeletal muscle, kidney

•CPT1A = liver isoform of CPT1

• All reported cases of human deficiency of CPT1 are due to defect in the CPT1A

isoform

• Does not affect muscle, heart, brain, etc.

CPT1AFunction

•Responsible for the 1st and rate-limiting step in mitochondrial fatty acid oxidation

•Located in the outer (cytosolic) membrane of the mitochondrion

A Closer Look

Symptoms of “Classic” CPT1A

Deficiency•Occur after prolonged fast, when

glucose and glycogen stores become depleted

•Presents with hypoketotic hypoglycemia, fatigue, vomiting, liver dysfunction, and seizures

History of “Classic” CPT1A Deficiency• Deficiency is severe

• Less than 5% of enzyme activity

• Deficiency is rare

• 2004 review reported 30 cases worldwide

• First cases in Alaska diagnosed in 2004—confirmed by skin biopsy (only method of confirming CPT1A deficiency at the time)

• Found when Alaska changed to MS/MS to perform their newborn metabolic screens (NBMS)

• Doubled the world’s cases in the first year of screening

Expanded NBMS

•Before 2004 in Alaska

• Hypothyroid

• PKU

• Galactosemia

• MSUD

• Biotinidase

• CAH

Expanded NBMS

•Utilizes tandem mass spectrometry (MS/MS) to screen for many more diseases than before

• Currently, Alaska screens for about 50 diseases

Expanded NBMS

•After 2004

• Added amino acid and urea cycle disorders

• Organic acid disorders

• CF

• Hemoglobinopathies

• Fatty Acid Oxidation Disorders

Fatty Acid Oxidation

Disorders—NBMS• VLCADD

• SCADD

• CPT1

• MCADD

• One of the major drivers for expanded screening (Medium Chain Acyl CoA Dehydrogenase Deficiency)

• Fatty acid metabolism disorder that has been linked to increased infant mortality—SIDS

The Arctic Variant

•A missense mutation (P479L) found in all affected Alaska Native people•Same mutation found in Canadian and

Greenland Inuit populations, Siberian arctic populations, and in British Columbia First Nations populations

•Skin biopsy results showed that this mutation gives 20% enzyme activity

The Arctic VariantRegulation

•P479L occurs in a region of CPT1 responsible for regulation of activity•CPT1A is inhibited by malonyl CoA

•Malonyl CoA increases when carbohydrates are ingested

•Mutation causes protein to always be “on” by not allowing malonyl CoA to bind

Newborn Screening

•NBMS has now detected about 900 cases in Alaska since 2004

•However, we know we’re detecting the minority of cases—about 15%

•There are actually 750 infants with the P479L variant born per year in Alaska

• Can’t set the C0/C16+C18 ratio to detect all cases without large number of false positives—more later

Distribution

60-70%

50-59%

30-39%

20-29%

Percent of Native AlaskanNewborns who are CPT1A c.1436C>T Homozygotes

Questions Surrounding the Arctic Variant of

CPT1A• All of the infants who had a skin biopsy had 20%

residual activity—is this enough activity to eliminate symptoms?

•Why does this variant have such high prevalence in Arctic populations?

• Could the Arctic variant be a contributing factor to the higher rate of SIDS in the rural villages in Northern/Southwest Alaska?

1st Project• 5 families with a child between the ages of 3-5

years with the Arctic Variant of CPT1A flown to Doernbecher Children’s Hospital for an 18 hour fasting study

• Labs at 6, 12, 18 hours drawn: Chem7, insulin, acylcarnitines, free fatty acids, lactate, pyruvate, ketones (acetoacetate and 3-hydroxybutyrate)

• Hourly serum glucose starting at 6 hours of fasting

• MRS done to determine if fatty deposits occur in liver

Fasting ProjectContinued

•2 of the 5 kids became symptomatic with plasma glucose below 51

•One went below 40

•Ketones were not produced at any stage of the fast in any kid

•Suggests that fatty acid oxidation is fairly severely affected by the Arctic Variant

Fasting Project Continued

•Their livers were imaged using magnetic resonance spectroscopy. The hypothesis was that these kids will have fatty livers compared to controls because of their inability to metabolize fats efficiently—like classic CPT1A deficiency

•Actually, completely normal livers

Conclusions

•Even healthy 5 year olds with the Arctic Variant of CPT1 can’t utilize fats effectively and can become symptomatic if fasting is prolonged

• In children who are sick, the symptoms would occur faster and would be more severe

Questions Surrounding the Arctic Variant of

CPT1A• All of the infants who had a skin biopsy had 10-

25% residual activity—is this enough activity to eliminate symptoms?

•Why does this variant have such high prevalence in Arctic populations?

• Could the Arctic variant be a contributing factor to the higher rate of SIDS in the rural villages in Northern/Southwest Alaska?

Traditional DietPermanent Ketosis

• Arctic populations traditionally eat a diet of 80% fat, 15% protein, and less than 5% carbohydrate (mostly from muscle glycogen)

• Essentially a ketogenic diet, and their bodies get used to functioning without much glucose

• Fatty-acid oxidation generates ketones to be used for energy

• Spares the small amount of glucose present for the brain

Ketogenic Diet When Ketogenesis Is Not Working

Well?

• The Arctic variant of CPT-1A might be advantageous to people observing a traditional diet because of its insensitivity to malonyl-CoA

• If a ketogenic diet has to be interrupted due to lack of fatty foods, the sudden disruption causes severe weakness, nausea, and headaches

• Overcome by eating more carbohydrates, which are not readily available in the Arctic

Ketogenic Diet When Ketogenesis Is Not Working

Well?• Non ketogenic diet most common at the end

of winter, when low-fat meat is consumed--more muscle glycogen

• If the Arctic variant of CPT1A is not inhibited by malonyl CoA with carbohydrate ingestion, then ketogenesis would tend to continue, and the malaise would occur less frequently and less severely

• Could allow for increased survival in a unforgiving environment

Also

•Marine mammals have high levels of n-3 polyenoic fatty acids, which increases the transcription of the CPT1A gene

•These fatty acids are passed into breast milk

•May off-set the 80% drop in activity

Possible New Study

•Compare people with the Arctic Variant who have a traditional diet vs. a more Western diet and compare symptoms, labs, and fasting ability.

Questions Surrounding the Arctic Variant of

CPT1A• All of the infants who had a skin biopsy had 10-

25% residual activity—is this enough activity to eliminate symptoms?

•Why does this variant have such high prevalence in Arctic populations?

• Could the Arctic variant be a contributing factor to the higher rate of SIDS in the rural villages in Northern/Southwest Alaska?

CPT1A and SIDS

Region # Deaths IMRNorthern 83 12.1*

Southwest 123 10.8*

Anchorage Bowl

425 6.3

Gulf Coast 84 6.2Interior 140 6.2

Southeast 79 6.2

Infant mortality rates (IMR) 1992-2004

Distribution

60-70%

50-59%

30-39%

20-29%

Percent of Native AlaskanNewborns who are CPT1A c.1436C>T Homozygotes

Phenotype of the Arctic Variant

• Looked at all Alaska Native infant deaths from 2006-2010

• 110 deaths

• 46 homozygous for the Arctic Variant

• Case control study comparing to 395 Alaska Native controls from the same time period

• 119 were homozygous for the Arctic Variant

Comparison of Arctic Variant to

Controls   CPT1A homozygous

among casesCPT1A homozygous among controls

Odds ratio (95% CI) Adjusted* odds ratio (95% CI)

All birth weights        

All study subjects 46 of 110 (42%) 119 of 395 (30%) 1.7 (1.1, 2.6) 1.8 (1.1, 2.9)

Limited to homozygous variant and heterozygous cases

46 of 79 (58%) 119 of 269 (44%) 1.8 (1.1, 2.9) 2.3 (1.3, 4.0)

Limited to residents of Western and Northern Alaska

38 of 58 (66%) 112 of 185 (51%) 1.8 (0.98, 3.3) 2.5 (1.3, 5.0)

Normal birth weights        

All study subjects 39 of 94 (41%) 112 of 377 (30%) 1.7 (1.1, 2.7) 1.8 (1.1, 2.9)

Limited to homozygous variant and heterozygous cases

39 of 69 (56%) 112 of 258 (43%) 1.7 (0.99, 2.9) 2.2 (1.2, 3.9)

Limited to residents of Western and Northern Alaska

33 of 48 (69%) 88 of 154 (51%) 2.2 (1.1, 4.2) 3.0 (1.4, 6.3)

*Adjusted for maternal education, a composite variable combining marital status and presence of the father ’s name on the birth certificate, and maternal prenatal alcohol and tobacco use.

Comparison of the Causes of Infant

Mortality

Cause of deathHomozygous variant (n=46)

Heterozygous or homozygous wildtype (n=66) OR (95%CI)

SIDS or asphyxia of unknown etiology 14 32 0.50 (0.22 to 1.1)

Infectious disease 12 7 2.9 (1.0, 8.0)

Congenital anomaly 8 12 0.91 (0.34, 2.4)

Injury 5 6 1.2 (0.38, 3.6)

Phenotype of the Arctic Variant

•Other findings in babies homozygous for the Arctic Variant

• More likely to have been diagnosed with an infectious disease before the clinical illness leading to their death

• Pneumonia was the strongest association

• More likely to have been hospitalized before their death

Conclusions•Looks like the presence of the Arctic

Variant of CPT1A could be the reason for the difference in infant mortality between Northern/SW Alaska the rest of the State

• The Arctic Variant doesn’t cause death, but contributes when the baby has an infectious issue

• Not associated with SIDS, as originally hypothesized

Next Steps

•Is education enough?

• No!

•Do we need to identify all of these kids, given the data relating the Arctic Variant to infant mortality?

• Yes!

Change the NBMS•If we lower the cutoff value for the

NBMS, we will pick up many more kids

• But also a lot of false positives

•Instead, we’re going to be using PCR on all NBMS cards to truly identify all kids with the Arctic Variant

• The Oregon Public Health Lab and State of Alaska are looking at the logistics

Recommendations for Parents

•Symptoms include:

• Poor feeding

• Lethargy

• Jitteriness

• Seizures

• Inconsolability

• Other symptoms of low blood sugar…..

Recommendations for Parents

•Until the NBMS is 100% sensitive, all babies from Western and Northern Alaska should be considered to be positive for the Arctic Variant

•Most babies never have any issues with the Arctic Variant of CPT1A

•Well babies almost NEVER have issues

Recommendations for Parents

•If your baby is sick, your baby shouldn’t go more than 6-8 hours without being able to drink breast milk, formula, or Pedialyte

•If your baby is going to have surgery, you should tell the doctor that your baby has the Arctic Variant of CPT1A

• People with Artic Variant shouldn’t be fasted for long periods of time

Other Effects

•In Greenland Inuit people, homozygotes for the Arctic variant have higher levels of HDL

•Unknown if this affects cardiovascular disease

Unknown

•Does the Arctic variant of CPT1A play a role in other adult disease?

•Diabetes

Resources• You Tube video—sent by the State to all families with a child

diagnosed by NBMS

• https://www.youtube.com/watch?v=g-JRZ7PO3yk&feature=youtu.be

• Handout—very detailed

• http://www.newbornscreening.info/Parents/fattyaciddisorders/CPT1AV.html

• Alaska Dispatch News article

• http://www.adn.com/article/20141129/clues-emerging-about-arctic-gene-diet-and-health

• American Indian Living with Dr. David DeRose

• http://stream.publicbroadcasting.net/production/mp3/nv1/local-nv1-1039242.mp3

But Wait…..Congenital Sucrase

Isomaltase Deficiency (CSID)•Sucrase Isomaltase enzyme

complex is missing from small intestine

•Can’t break down sucrose into fructose and lactose

•Can’t break starch down completely due to decreased isomaltase activity

CSID•Autosomal recessive

• Frameshift mutation that causes absence of enzyme

• Can now send a blood test to the University of Washington to test for the Alaska Native-specific mutation

•Results in osmotic diarrhea when weaned from breast milk/formula, or table foods are introduced

• Has a varied phenotype, ranging from severe diarrhea with FTT to more of an irritable bowel syndrome picture

More CSID•Prevalence

•0.2% of the general population

•5-10% of Greenland/Canadian Inuit people

•Unknown at this time in Alaska Native people—but we’re finding out it’s probably similar to the Greenland/Canadian Inuit people

CSID Treatment•Diet control—Avoid foods with

processed sugar and foods high in sucrose and starch

• Peas, beets, onions, pastas, breads, potatoes, honey

• Alaska Native Traditional Diet is actually perfect for CSID control

•In the absence of diet control, Sucraid can be used

• Very expensive, and needs to be taken with every meal and snack

Thanks—Arctic VariantCPT1AOregon Health & Sciences

UniversityDavid KoellerMelanie GillinghamBill LambertCary HardingSarah Lowe

State of Alaska DHSSThalia WoodStephanie BirchBrad Gessner

Alaska Native Medical CenterTerry Powell Doug EbySamantha MaloneyAll Pediatric Staff

University of ManitobaCheryl Greenberg

Fatty Acid Oxidation