1. Inborn Errors of Metabolism
Michael Marble, MD
Professor of Clinical Pediatrics
Division of Clinical Genetics
Department of Pediatrics, LSUHSC
and Children’s Hospital

2. A 3 day old male is brought to the emergency room with a history of lethargy progressing to unresponsiveness. You take an initial history which reveals that the baby had been feeding normally for 24 hours but thereafter became irritable and lost interest in feeding. On exam, you notice that he is breathing fast and deep and is unresponsive. Along with other possible diagnoses, you suspect metabolic disease.
(1) Which laboratory studies would you order to obtain quick evidence for or against metabolic disease?
(2) You obtain a complete metabolic profile which shows a normal result. Urinalysis shows elevated specific gravity but is otherwise normal. Capillary blood gas shows respiratory alkalosis: 7.53/ pCO2 20/HCO3 nl, BE nl
(3) Based on these results, what type of metabolic disease is most likely? Which test would you order next?
Urea cycle disease; plasma ammonia
(4) Plasma ammonia result is 1400 micromole/L (0-80). What is the most likely diagnosis? Which tests would you send to confirm a specific metabolic disorder?
Ornithine transcarbamylase deficiency. Plasma amino acids, urine orotic acid
You confirm that the patient has ornithine transcarbamylase deficiency. What is the recurrence risk in the next pregnancy? Who else in the family should be tested?
X-linked inheritance therefore 50% recurrence risk if mother is a carrier.
(6) What is the treatment?
Hemodialysis, low protein diet, arginine, phenylbutyrate

3. OTC deficiency is the most common and is X-linked
Urea Cycle Disorders
DIET +
Carbamoyl Phosphate
Protein
NH4+
HCO3
Hyperammonemia without metabolic acidosis (usually have respiratory alkalosis)
OTC
Ornithine
Citrulline
UREA
CYCLE
Urea cycle disorders:
Ornithine transcarbamylase deficiency (X-linked)
Carbamoyl phosphate synthase deficiency (AR)
Citrullinemia (AR)
Argininosuccinic acidemia (AR)
Argininemia (AR)
Asp (N)
Arginine
urea(2N)
Argininosuccinic Acid
OTC deficiency is the most common and is X-linked

4. Headaches, recurrent vomiting, avoids meat
X-linked inheritance, partially affected female 4

5. 136 101 26 96 Ammonia 646 (0-36) UA 3+ ketones 4.8 10 0.7
A 3 day old male is brought to the emergency room with a history of lethargy progressing to unresponsiveness. You take an initial history which reveals that the baby had been feeding normally for 24 hours but thereafter became irritable and progressively less interested in feeding. On exam, you notice immediately that he is breathing fast and deep and is unresponsive. Along with other possible diagnoses, you suspect metabolic disease.
(1) Which laboratory studies would you order to obtain quick evidence for or against metabolic disease?
(2) You obtain a blood gas, basic metabolic profile, urinalysis and plasma ammonia which show the following:
136
101 26 96
Capillary blood gas:
7.11/CO2 19, HCO3 9, BE - 11
Ammonia 646 (0-36)
UA 3+ ketones
4.8 10
0.7
(3) Based on these results, what type of metabolic disease is most likely?
Organic acidemias (this patient has propionic acidemia)
(4) How would you confirm a specific metabolic disorder in this case?
Urine organic acids, plasma acylcarnitine profile

6. methylmalonic acidemia
Organic Acids
Anabolic
Catabolic
ATP
Isoleucine
Valine
Methionine
Cholesterol
Odd chain fatty acids
propionic acidemia
methylmalonic acidemia
biotin
B12
Propionyl CoA
Methylmalonyl CoA
Succinyl CoA
Bicarb is used to buffer the propionic acid, leading to increased anion gap
Krebs Cycle
isovaleric acidemia
leucine
Isovaleryl CoA
3MCC
HMG CoA
Acetyl CoA
ETS
Even chain fatty acids
Lysine
Tryptophan
glutaric acidemia
ATP
Acetyl CoA
Glutaryl CoA
Crotonyl CoA
Organic acids are the intermediates in the catabolism of amino acids, lipids and other compounds; specific enzyme deficiencies lead to characteristic urine organic acid profiles

7. Organic acids are metabolized in the mitochondria; blocks in their metabolism lead to elevation of specific acylcarnitines which are identified by plasma acylcarnitine profile
Long chain fatty acid
Fatty acid
Detected by acylcarnitine profile
Fatty acyl-CoA
Free carnitine
Fatty acyl-carnitine
Propionyl CoA
propionylcarnitine
Fatty acyl-carnitine
Free carnitine
acetyl CoA
Krebs
CoA
Fatty acyl-CoA
Fatty acid oxidation
ketones
Mitochondrion
Plasma
Cytoplasm

8. Selected Organic Acidemias Wide anion gap ketoacidosis
Disease
Cofactor
Other features
Propionic
Methylmalonic
Isovaleric
Glutaric
Maple syrup urine
biotin
B12
riboflavin
thiamine
Usually severe
Some respond to B12
Sweaty foot odor to urine
Macrocephaly, dystonia,
Maple syrup odor, elevated branched chain amino acids + + + +
Abnormal MRI +

9. Glutaric Acidemia Type 1
Severe movement disorder

10. Glutaric acidemia type 1
(patient with viral illness)
Intercurrent illnesses (usually viral) greatly increase the risk of metabolic encephalopathy and long term disability; therefore preventive measures against catabolism are critical
The parents of organic acidemia patients should be given emergency protocols for management during intercurrent illnesses
D10 + ¼ NS at 1.5 maintenance volume; IV carnitine

11. Urea cycle disease versus organic acidemias
UCD OA
lethargy/coma
vomiting
hyperammonemia
metabolic ketoacidosis
primary respiratory alkalosis + + + + + +
+/- - + + -

12. (1) What is the most likely diagnosis? Nonketotic hyperglycinemia
You are called to the newborn nursery regarding an 8 hour old female who is listless and not interested in feeding. The baby is severely hypotonic and lethargic but no other obvious abnormalities are noted. Accucheck shows normal glucose. Blood gas, complete metabolic profile, CBC, plasma ammonia, lactate and urinalysis all show normal results. Chest X-ray comes back normal. Along with other possibilities, you suspect a neuromuscular disorder and consult neurology. Maintenance IVFs are started. Pregnancy history is significant for decreased fetal movements. While awaiting neurology consult, the baby has apnea spells and develops myoclonic jerks. and is intubated. An EEG shows a “burst suppression” pattern.
(1) What is the most likely diagnosis?
Nonketotic hyperglycinemia
(2) How would you confirm the diagnosis?
CSF/plasma glycine ratio
(3) What is the prognosis?
Very poor, despite treatment

13. Nonketotic hyperglycinemia
*Defect in glycine catabolism
Glycine
NH3 + CO2
autosomal recessive
symptoms in first 24 hours
hypotonia/encephalopathy, seizures, burst suppression EEG
increased CSF/plasma glycine
Tx: benzoate, dextramethorphan
poor prognosis, diet ineffective
*Diagnosis based on elevated CSF/Plasma glycine ratio 13

14. CBC: WBC mildly elevated
A 15 month old female, previously healthy, was brought to the emergency room after the mother had difficulty arousing her in the morning. Over the past 2 days, the child had had a low grade fever, cough, mild diarrhea and 3 episodes of vomiting. Due to poor appetite, the patient did not eat very much for dinner and missed her ususal bedtime snack the night before presentation. In the ER, she was noted to have a depressed mental status but was partially responsive. Exam was otherwise normal. Initial lab testing showed the following:
CBC: WBC mildly elevated
CMP shows sodium 139, Cl 104, CO2 13 BUN 28 Cre 0.6, glucose 37, mild elevation of ALT and AST
Urinalysis negative for reducing substances and ketones, specific gravity is elevated
The ER physician starts an IV and gives a bolus of glucose to correct hypoglycemia. The physician also gives normal saline boluses for rehydration. Then IVFs with D5 ¼ normal saline is started at 1.5 maintenance fluids. Followup labs show normal serum glucose but no change in acid-base status. The patient’s mental status worsens and she becomes comatose. She is transferred to the PICU. Plasma ammonia level is found to be mildly elevated at 101 micromoles/L .
Patient who presented with hypoglycemia and altered mental status
Based on the above presentation and lab results, the patient most likely has a disorder within which category of inborn error of metabolism?
Fatty acid oxidation defects (specifically MCAD in this patient)
How would you confirm a specific diagnosis?
Plasma acylcarnitine profile

15. Diagnosis of fatty acid oxidation disorders by acylcarnitine analysis
Long chain fatty acid
Fatty acid
Detected by acylcarnitine analysis
MCAD deficiency
Fatty acyl-CoA
Fatty acyl-carnitine
(C6-C12)
(C6-C12)
Free carnitine +
fatty acyl CoAs
Fatty acyl-carnitine
Fatty acyl-carnitine
acetyl CoA
Fatty acyl-CoA
SCAD 18 16 14 12 8 6 4
MCAD
ketones
Mitochondrion
Plasma
Cytoplasm

16. *key pathway for adaptation to fasting
Fatty acid oxidation
Brain
CPT1/CPT2
ketones
Fatty acids
VLCAD LCHAD MCAD SCAD +
fasting
acetyl CoA
*key pathway for adaptation to fasting
Krebs cycle
Distinguishing feature of FAOD is hypoketotic hypoglycemia
Medium chain acyl CoA dehydrogenase deficiency(MCAD) is most common and has a 25% risk of death with first episode
LCHAD, VLCAD and carnitine uptake disorder are variably associated with, hepatomegaly, liver disease, hypertrophic cardiomyopathy and potential arrythmias
All are autosomal recessive 16

17. Hypoketotic hyoglycemia, hypotonia, failure to thrive
LCHAD deficiency
Hypoketotic hyoglycemia, hypotonia, failure to thrive
At diagnosis
On dietary treatment 17

18. Variable Clinical presentations of fatty acid oxidation
Hyoketotic hypoglycemia in neonatal period
Later onset hypoketotic hypoglycemia
Sudden infant death syndrome
Hypertrophic cardiomyopathy, arrythmias
Liver disease
Adolescent or adult onset myopathy
Acute rhabdomyolysis
Asymptomatic

19. Fatty acid oxidation disorders
Typical presentation
Disease
Comments
SCAD
Probably benign
N/A
Hypoketotic hypoglycemia
Most common FAOD, may be associated with “SIDS”
MCAD
VLCAD
Variable: hypoketotic hypoglycemia, hypertrophic cardiomyopathy, myopathy, liver dz
Extemely variable ranging from neonatal to adult onset
LCHAD
Variable: hypoketotic hypoglycemia, hypertrophic cardiomyopathy, myopathy, liver dz
Extremely variable, need low fat diet
Diagnosis is based on the specific pattern of acylcarnitine elevations

20. Disorders of carnitine metabolism MCAD, organic acidemias etc
Carnitine transports long chain fatty acids into the mitochondria
Carnitine deficiency can be primary or secondary
Primary carnitine deficiency is caused by abnormal transport of carnitine itself into the cells (carnitine uptake disorder, AKA “systemic carnitine deficiency”)
Secondary carnitine deficiency is caused by other metabolic disorders through the formation of carnitine esters (acylcarnitines) by abnormal organic/fatty acids
Primary (CUD)
MCAD, organic acidemias etc
Plasma:
Decreased/normal total carnitine
Decreased free carnitine
Increased acyl/free ratio
Plasma:
Decreased total carnitine
Decreased free carnitine
Normal acyl/free ratio
Urine:
Decreased/normal total carnitine
Decreased free carnitine
Increased acyl/free ratio
Urine:
Normal total carnitine
Normal or increased free carnitine
Normal acyl/free ratio

21. Which metabolic disorder do you suspect? galactosemia
A 6 day old female who is breast fed is brought to the emergency room due to poor feeding, vomiting and jaundice? Initial laboratory studies show the following:
Total Bilirubin 19
Direct bilirubin 5.2
136
115 26
AST 987
ALT 767 73
4.8 10
0.7
Which metabolic disorder do you suspect?
galactosemia
Which other routine tests should you order?
PT, PTT, urine reducing substances
How would you confirm the diagnosis?
Enzyme assay, DNA
How would you treat this patient?
Galactose free diet
What are the acute and long term complications of this disorder?
Liver disease, E coli sepsis, cataracts, MR, speech delay, ovarian failure

22. galactose-1-P uridyltransferase
Galactose Metabolism
glucose
(cataracts)
Breast milk, cow’s milk
galactokinase
Galactose
Lactose
Gal-1-P
(galactose-glucose)
UDP glucose
galactose-1-P uridyltransferase
epimerase
(benign)
UDP galactose
(classical)
Glucose-1-P
Treatment: galactose free diet, ophthalmology and developmental followup
Glucose-6-P
glycolysis
pyruvate 22

23. What is the most likely metabolic diagnosis?
A 9 year old male is brought to the emergency room due to acute vomiting and lethargy shortly after a birthday party. Past medical history is significant for failure to thrive in late infancy which resolved without determination of a diagnosis. He had had several bouts of vomiting in the past, usually after consuming candy or soft drinks at parties. He has had no dental cavities. Laboratory results in the ER are as follows:
Total Bilirubin 6.4
Direct bilirubin 5.2
136
115 26
AST 767
ALT 987 73
4.8 10
0.7
What is the most likely metabolic diagnosis?
Hereditary fructose intolerance

24. What is the most likely diagnosis? Glycogen storage disease
A 3 month old female is found to have hepatomegaly on routine exam. She is asymptomatic. Lab testing shows hypoglycemia, lactic acidemia, hyperuricemia, hyperlipidemia and elevated AST and ALT.
What is the most likely diagnosis?
Glycogen storage disease
How would you confirm the diagnosis?
DNA, liver biopsy
What is the treatment?
dietary 24

25. Glycogen Storage Disease 1a
“Von Gierke disease”

26. Glycogen Storage Disease 1b
facial features
hepatomegaly
Hypoglycemia, lactic acidosis, hyperuricemia, hyperlipidemia, neutropenia
weakness 26

27. Sibling with same disorder
Autosomal recessive 27

28. Glycogen Glucose – 1- P Glucose – 6- P Glucose glucose
Krebs cycle
Glycogen is a storage form of glucose:
Liver glycogen releases glucose into the circulation
Muscle glycogen is used locally
Lactic acidosis
Acetyl CoA
pyruvate
Glucose – 1- P
Malonyl CoA
gluconeogenesis
glycolysis
Stimulates fatty acid synthesis and inhibits fatty acid breakdown
(Hyperlipidemia)
Pentose phosphate shunt
(hyperuricemia)
Glucose – 6- P ER
Glucose-6-phosphatase
GSD types 1a and 1b
Glucose
cytoplasm
Glut 2
plasma
glucose 28

29. Selected glycogen storage diseases
Typical presentation
Disease
Other features
Treatment
Von Gierke (GSDIa)
Hepatomegaly, lactic acidosis, hyperuricemia, hyperlipidemia
Puffy cheeks
Nocturnal NG feedings, avoid fasting
GSDIb
Hepatomegaly, lactic acidosis, hyperuricemia, hyperlipidemia
Nocturnal NG feedings, avoid fasting, neutropenia precautions
Puffy cheeks, neutropenia
Pompei (GSD II)
Weakness, hypotonia, cardiomyopathy
EKG: short PR intervals, wide QRS
Enzyme replacement
Debrancher deficiency (GSD III)
Similar to Von Gierke but milder, normal lactate
Muscle, including cardiac may be involved
Similar to GSD1a
Brancher deficiency (GSD IV)
Fatal liver disease (amylopectinosis)
Other organ involvement
? transplant
McCardle disease (GSD VI)
Only muscle involvement
Avoid excess excercise
Risk of rhabdomyolysis

30. Patient with developmental regression
Apparently normal development for the first 6 months but begins to slow down. She was able to sit unassisted by 1 year. She was very socially interactive and could grasp objects. Gradually lost her ability to sit and grasp objects. Became less and less interactive, and lost interest in eating and became emaciated. She had splenomegaly. Ophthalmology exam revealed a cherry red spot macula:
What type of disorder do you suspect?
Lysosomal storage disease
How would you confirm a diagnosis?
Enzyme assay
What is the differential diagnosis of cherry red macula? 30

31. Lysosomal storage disease: ocular features
Lysosomal lipid storage disorders associated with cherry red macula:
Niemann-Pick A
Tay-Sachs disease
GM1 gangliosidosis
Sandhoff disease
Farber lipogranulomatosis
Sialidosis 31

32. Lysosome “The cells wrecking crew”
Cell membranes, organelles
Bone, connective tissue, skin, cornea,joints etc
Sphingolipids, glycolipids etc
Mucoploysaccharides (glycosaminoglycans)
Glycoproteins
Glycogen
Food particles
Bacteria, viruses
Acid hydrolases
Lysosome
Abnormal lysosomal storage leads to developmental regression
“The cells wrecking crew” 32

33. Metachromatic Leukodystrophy
Rapid developmental regression starting in late infancy
Lysosomal accumulation of sulfatides

34. GM1 Gangliosidosis
Neonatal presentation: hypotonia, ascites

35. A 14 month old female presented with developmental delay to your clinic. She was reportedly normal at birth but at 8 months was noted to have mild kyphosis when sitting. She had chronic rhinorrhea. Late in infancy, the parents noticed gradual changes in craniofacial features including thickening of the eyebrows, large tongue, prominence of forehead. The patient hand been pulling to stand but lost this ability and seemed to be regressing in overall development. On exam, you notice a scaphocephalic head shape, frontal bossing, relatively thick eyebrows, cloudy cornea and stiff elbows.
The patient most likely has a disorder within which category of inborn error of metabolism?
Lysosomal storage disease (mucopolysaccharidosis)
How would you confirm a specific diagnosis?
Enzyme assay, urine mucopolysaccharies (glycosaminoglycans), skeletal survey

36. Mucopolysaccharidosis
Hurler Syndrome: comparison with sibs

37. Hurler syndrome

38. Mucopolysaccharidosis
Hurler syndrome – alpha L-iduronidase def.
organomegaly

39. Sanfilipo Syndrome (MPS 3)
facial features
Sanfilipo (MPS III)
Less severe somatic features
Developmental delay
Behavioral problems
Neurological regression

40. Maroteaux-Lamy (MPS VI)

41. Maroteaux-Lamy syndrome (MPS6)

42. Morquio (MPS IV)

45. Lysosomal storage disease: laboratory diagnosis
Urine mucopolysaccharides
Urine oligosaccharide
Enzyme assay
DNA (for genetic counseling and to rule out pseudoalleles)

46. Typical presentation Disease Inheritance Treatment Hurler (MPS1)
Developmental regression, dysosotosis multiplex, cloudy cornea, organomegaly, cardiac valve disease
Autosomal recessive
BMT/ERT
Hunter (MPS2)
Similar to Hurler but no cloudy cornea
X-linked
BMT/ERT
San Filippo (MPS3)
Later onset, mild somatic features
Autosomal recessive
Morquio (MPS4)
Mainly skeletal involvement
Autosomal recessive
?ERT
Maroteaux-Lamy (MPS6)
Similar to Hurler but “CNS sparing”
Autosomal recessive
BMT/ERT

47. One year old female with failure to thrive, developmental delay and hypotonia, MRI showed basal ganglia abnormalities. Labs show mild elevation of lactate.

48. Mitochondrial genome sequencing: mutation m
Mitochondrial genome sequencing: mutation m.8993T>G in a subunit of ATP synthase

49. Mitochondrial genome disorders
Maternal inheritance
Heteroplasmy
Replicative segregation

50. Mitochondrial genome disorders
Myoclonic epilepsy, lactic acidosis, stroke-like episodes (MELAS)
Myoclonic epilepsy ragged red fibers (MERRF)
Neuropathy, ataxia, retinintis pigmentosa (NARP)
Nonsyndromic deafness/diabetes
Kearn Sayres: sporadic giant deletions
Pearson syndrome: sporadic giant deletions
Leigh syndrome
other

51. PKU Adult with Mental Retardation: born before newborn screening era
PAH
Dietary protein
Phe
Tyr
Neurotransmitters, melanin etc
Phenylalanine hydroxylase defect
Autosomal recessive
Normal infant at birth
Severe mental retardation, microcephaly, behavioural problems

52. PKU: Clinical Problems if Untreated
mental retardation
seizures
hypopigmentation
rash
Tx: low phenylalanine diet
*Due to newborn screening, the above problems
rarely occur.

53. If obtained too early, false negative
“Guthrie cards”
Heel stick:
Obtain at about 48 hours
If obtained too early, false negative
Filter paper with blood spots and demographic information

54. Normal growth and development
Phenylketonuria
Patients with PKU: low Phe diet, frequent monitoring of Phe, dietary counseling
Studies have shown that NBS has virtually eliminated mental retardation due to PKU
Normal growth and development

55. Selected Presentations/Diagnostic Considerations
Lysosomal storage (MPS)
GLYCOGEN
STORAGE
DISEASE (MUSCLE)
Or FAOD
Lysosomal storage (glycolpids))
WEAKNESS
RHABDOMYOLYSIS
DEVELOPMENTAL
REGRESSION
SKELETAL DYSPLASIA
ORGANOMEGALY
VARIABLE CLOUDY CORNEA
GLYCOGEN
STORAGE
DISEASE (LIVER)
DEVELOPMENTAL
REGRESSION
ORGANOMEGALY
CHERRY RED MACULA
HYPOGLYCEMIA
HEPATOMEGALY
HYPERCHLOREMIC
METABOLIC ACIDOSIS
LIVER DISEASE
CATARACTS
HYPERBILIRUBINEMIA
REDUCING SUBSTANCES
INFANT/CHILD WITH SUSPECTED METABOLIC DISEASE
RESPIRATORY ALKALOSIS
HYPERAMMONEMIA
UREA CYCLE DISEASE
GALACTOSEMIA
METABOLIC ACIDOSIS
HYPOGLYCEMIA
INAPPROPRIATELY LOW KETONES
KETONES NEGATIVE ENCEPHALOPATY < 24 HRS OLD, BURST SUPPRESSION EEG
WIDE ANION GAP METABOLIC ACIDOSIS, KETONURIA, HYPERAMMONEMIA
FATTY ACID OXIDATION DEFECT
ORGANIC ACIDEMIA
NON KETOTIC HYPERGLYCINEMIA