approach to Inborn Errors of Metabolism in neonates

DR.GOKULDAS P K Junior resident in PediatricsGovt.medical college, Kozhikkode

Approach to Inborn errors of metabolism in Neonates

Introduction to IEM

Differential diagnosis of any sick neonate

IEM are individually rare

Overall incidence upto 1 in 2000

High index of suspicion for diagnosis

Clinical pointers

Deterioration after a period of apparent normalcy

Parental consanguinity

Family history of neonatal deaths

Rapidly progressive encephalopathy and seizures

of unexplained cause

Severe metabolic acidosis

Clinical pointers

Persistent vomiting

Peculiar odor

Acute fatty liver or HELLP (long-chain-3-

hydroxyacyl-coenzyme dehydrogenase

deficiency (LCHADD).

Clinical presentati ons

Neurologic deteriorationWith metabolic acidosis

• MSUD• organic acidurias• fatty acid oxidation defects• Primary lactic acidemias (defects of

gluconeogenesis, glucogenolysis, pyruvate metabolism, Krebs cycle, and respiratory chain)

Neurologic deterioration

With hypoglycemia

• organic acidurias

• fatty acid oxidation defects

• defect of gluconeogenesis

Neurologic deterioration

With hyperammonemia

• Urea cycle defects

• Propionic acidemia

• Methyl malonyl acidemia

Seizures

Seizures

Non-ketotic hyperglycinemia in uteroPyridoxine –responsive seizures, 1st dayPyridoxal phosphate responsive seizures 1t

dayFolinic-acid responsive seizures 1st daySulfite oxidase/molybdenum co-factor defect Peroxisomal disordersDisorders of creatine biosynthesis & transport

Hypotonia

Mitochondrial respiratory chain defects

Peroxisomal disordersNon-ketotic

hyperglycinemiaSulfite

oxidase/molybdenum co-factor defect

Liver dysfunction

Hepatomegaly with hyoglycemiaGluconeogenesis defects(GSD)

Liver failureGalactosemiaHereditary fructose intolerancetyrosinemia type IFAO defectsMitochondrial respiratory chain defects

Cholestatic jaundice with failure to thrive:

alpha-1-antitrypsin deficiency

Niemann-Pick disease type C

Inborn error of bile

acid metabolism

Peroxisomal disorders

Citrin deficiency

Cardiac dysfunction

Fatty acid oxidation defects

Carnitine uptake deficiency

Carnitine-acyl Carnitine translocase deficiency

Carnitine palmitoyl transferase ll deficiency

LCHAD deficiency

Trifunctional protein deficiency

VLCAD deficiency

Cardiac dysfunction

Glycogen storage diseasesPompe diseasePhoshorylase b kinase deficiency

Mitochondrial electron transport chain defectsTCA cycle defects

Alpha keto glutarate dehydrogenase deficiencyLysosomal storage disorder

I -cell disease

Apnea

Long Chain Fatty acid oxidation defects

Non ketotic hyperglycinemia

Abnormal urine odor

Glutaric acidemia (type II):Sweaty feetIsovaleric acidemia: Sweaty feet

Multiple carboxylase deficiency: Tomcat urine

Maple syrup urine disease: Maple syrup odour of urine

Hypermethioninemia: Boiled cabbage urine odor

Miscellaneous

Lens dislocation : Sulfite oxidase deficiency

Skin changes : Biotinidase deficiency HCS deficiency

Dysmorphic Features

Peroxisomal disorders : Zellweger syndromeLarge fontanelle prominent forehead flat nasal bridge epicanthal folds hypoplastic supraorbital

ridges

Dysmorphic Features

Pyruvate dehydrogenase deficiencyEpicanthal folds flat nasal bridge small nose with

anteverted flared alae nasi

long philtrum

Dysmorphic Features

Glutaric aciduria type IIMacrocephaly high forehead flat nasal bridge short anteverted nose ear anomalies hypospadias rocker-bottom feet

Dysmorphic Features

Cholesterol biosynthetic defects Smith-Lemli-Opitz

syndrome: Epicanthal folds, flat nasal

bridge, toe 2/3 syndactyly, genital abnormalities, cataracts

Dysmorphic Features

Congenital disorders of glycosylation: Inverted nipples, lipodystrophy

Lysosomal storage disorders: I-cell disease Hurler-like phenotype

Hydrops fetalis

Lysosomal disordersMPS type I, IV A, & VIIGM 1 gangliosidosisGaucher diseaseNiemann Pick disease type CSialidosis Galactosialidosis Farber disease

Hematologic disordersGlucose-6-phosphate dehydrogenase deficiencyPyruvate kinase deficiencyGlucosphosphate isomerase deficiency

OthersCongenital disorders of glycosylationNeonatal hemochromatosisRespiratory chain disordersGlycogen storage disease type IV

Investi gati ons

Initial evaluation

Complete blood count Arterial blood gases and electrolytes Blood glucose Plasma ammonia Arterial blood lactate Liver function tests

Initial evaluation

Urine ketones if acidosis or hypoglycemia present

Urine reducing substances. Serum uric acid (low in molybdenum cofactor

deficiency).Plasma amino acids, quantitative

Laboratory studies if seizures present

Cerebrospinal fluid (CSF) amino acids

CSF neurotransmitters

Sulfocysteine in Urine

VLCFA

Lactate : pyruvate ratio: Respiratory chain defects

Complete blood cell count :

Neutropenia and

thrombocytopenia : Isovaleric

acidemia, methylmalonic

acidemia , and propionic

acidemia .

Neutropenia :Glycogen storage

disease type 1b Barth syndrome

and Pearson syndrome.

Serum electrolytes

& Blood gases

Acidosis/ alkalosis &

types

Anion gap ( organic

acidemias &

primary lactic

acidosis

High lactate

Euglycemia Hypoglycemia Euglycemia Hypoglycemia

Normal lactate

No ketosis

Ketosis +

Metabolic acidosis

MSUD Organic aciduria

PC deficiency,

HCS deficiency

GSD1, Gluconeogenesis defects, Respiratory

chain defects

NEXT

SLIDE

HypoglycemiaEuglycemia

High lactate Normal lactate

No ketosis

FAO defectPDH deficiency Renal tubular acidosis

Hyperammonemia

Metabolic acidosis Respiratory alkalosis

Plasma citrulline

Organicaciduria,

FAO defects, Primary lactic

acidosis

Urea cycle defects

Plasma citrulline

Low Normal High

Urine orotic acid

Elevated

Plasma ASAPlasma arginine

Normal Normal Normal Elevated Elevated

OTC deficiency

CPS deficiency

NAGS deficiency

Arginase deficiency

HHH ASL deficiency

ASS deficiency

Liver function tests

Galactosemia

Tyrosinemia

Alpha-1-antitrypsin deficiency

Neonatal hemochromatosis

mitochondrial respiratory chain disorders

Niemann-Pick disease type C.

Urine-reducing substances, ketones & pH

Clinitest reaction :galactose and glucose, but not fructose

Clinistix reaction (glucose oxidase) specific for glucose

pH <5 indicate IEM

Ketonuria is abnormal in neonates

Dinitrophenylhydrazine :α-ketoacids in MSUD.

Plasma carnitine and acylcarnitine profile

Elevation of carnitine esters Fatty acid oxidation defectsOrganic acidemiasKetosis

low carnitine levelsDisorders of carnitine biosynthesisPreterm infants and neonates receiving total

parenteral nutrition without adequate carnitine supplementation.

Secondary carnitine deficiency.

Second line investigations• To be performed in a targeted manner

Gas chromatography mass spectrometry of urineOrganic acidemias.

Plasma amino acids and acyl carnitine profile: by tandem mass spectrometryOrganic acidemias Urea cycle defectsAminoacidopathies Fatty acid oxidation defects.

High performance liquid chromatography :Quantitative analysis of amino acids in blood

and urineOrganic acidemias and aminoacidopathies

Lactate/pyruvate ratio- in cases with elevated lactate.

Urinary orotic acid- in cases with hyperammonemia for classification of urea cycle defect.

Enzyme assay: This is required for definitive diagnosis, but not available for most IEMbiotinidase assay- biotinidase deficiency

(intractable seizures, seborrheic rash, alopecia)GALT (galactose 1-phosphate uridyl transferase )

assay- galactosemia (hypoglycemia, cataracts, reducing sugars in urine).

Neuroimaging: MRI

IEM may be associated with structural malformations e.g. Zellweger syndrome has diffuse cortical migration and sulcation abnormalities.

Neuroimaging: MRI

Agenesis of corpus callosum : Menke’s diseasePyruvate decarboxylase deficiency Nonketotic hyperglycinemia

Neuroimaging: MRI

Glutaric aciduria type II: frontotemporal atrophy, subdural hematomas

Neuroimaging: MRI

MSUD: brainstem and cerebellar edema

Propionic & methylmalonic acidemia: basal ganglia signal change

Magnetic resonance spectroscopy : lactate peak elevated in mitochondrial disorders

leucine peak elevated in MSUD.

Electroencephalography (EEG):

Comb-like rhythm suggests MSUD

Burst suppression in NKH and holocarboxylase synthetase deficiency

Other investigations

Plasma very long chain fatty acid (VLCFA) levels: elevated in peroxisomaldisorders.

Mutation analysis when available.

CSF aminoacid analysis: CSF Glycine levels elevated in NKH.

Collecting samplesShould be collected before specific treatment

is started or feeds are stopped

Samples for blood ammonia and lactate should be transported in ice and immediately tested.

Lactate sample should be arterial or central line and should be collected after 2 hrs fasting in a preheparinized syringe.

Collecting samples

Ammonia sample is to be collected approximately after 2 hours of fasting in EDTA vacutainer. Avoid air mixing.

Sample should be free flowing.

Detailed history including drug details should be provided to the lab. (sodium valproate therapy may increase ammonia levels).

Metabolic autopsy

Samples to be obtained in infant with suspected IEM when diagnosis is uncertain and death seems inevitable

Blood: 5-10 ml; frozen at -200C; both heparinized (for chromosomal studies) and EDTA (for DNA studies)

Urine: frozen at –20oC

CSF: store at –20oC

Skin biopsy: including dermis in culture medium or saline with glucose. Store at 4-80C. Do not freeze.

Liver, muscle, kidney and heart biopsy: as indicated.

Clinical photograph (in cases with dysmorphism)

Infantogram (in cases with skeletal abnormalities)

MANAGEMENT OF INFANT AT RISK FOR A METABOLIC DISORDER

When a sibling has had symptoms consistent with a metabolic disorder, or has died of a metabolic disorder:

Before or during subsequent pregnancy

Prenatal discussion of possible diagnoses, and the parents and relatives should be screened for possible clues.

Old hospital charts and postmortem material should be reviewed.

When a diagnosis is known, intrauterine diagnosis to be tried.

The new baby should be delivered in a facility equipped to handle potential metabolic or other complications.

Initial evaluation includes a careful physical examination for the signs of IEM

All nonmetabolic causes of symptoms should be excluded.

The newborn screening program should be contacted for the results of the screening and for a list of the disorders screened.

Blood and urine tests before starting treatment for metabolic disease.

The specimens can be frozen (plasma, urine) and analysis performed later.

Enzyme assay of red blood cells, or enzyme and DNA analysis of white blood cells, fibroblasts, or liver tissue may be done for confirmation of diagnosis.

DNA analysis can sometimes be performed on a dried blood specimen (Guthrie blood spot).

In most cases, treatment needs to be instituted empirically without a specific diagnosis.

The metabolic screen helps to broadly categorize the patient’s IEM (e.g. urea cycle defect, organic academia, congenital lactic acidosis etc).

TREATMENT

Aims of treatment

Decreasing substrate availability (by stopping feeds and preventing endogenous catabolism)

To provide adequate calories

To enhance the excretion of toxic metabolites.

To institute co-factor therapy for specific disease and also empirically if diagnosis not established.

Supportive care- treatment of seizures (avoid

sodium valproate – may increase ammonia

levels)

maintain euglycemia and normothermia

fluid, electrolyte & acid-base balance

treatment of infection

mechanical ventilation if required.

Management of hyperammonemia

Discontinue all feeds. Provide adequate calories by intravenous

glucose and lipids. Maintain glucose infusion rate 6- 8mg/kg/min.

Start intravenous lipid 0.5g/kg/day (up to 3g/kg/day).

After stabilization gradually add protein 0.25 g/kg till 1.5 g/kg/day.

Dialysis is the only means for rapid removal of ammonia, and hemodialysis is more effective and faster than peritoneal dialysis. Exchange transfusion is not useful.

Sodium benzoate (IV or oral)- loading dose 250 mg/kg then 250-400 mg/kg/day in 4 divided doses. (not available in India).

L-carnitine (oral or IV)- 200 mg/kg/day

Sodium phenylbutyrate (not available in India)-loading dose 250 mg/kg followed by 250-500 mg/kg/day.

L-arginine (oral or IV)- 300 mg/kg/day (Intravenous preparation not available in India)

Suspected organic acidemia• Acute management The patient is kept nil per orally and

intravenous glucose is provided. Supportive care: hydration, treatment of

sepsis, seizures, ventilation. Carnitine: 100 mg/kg/day IV or oral. Treat acidosis: Sodium bicarbonate 0.35-

0.5mEq/kg/hr (max 1-2mEq/kg/hr)

Biotin 10 mg/day orally.

Vitamin B12 1-2 mg/day I/M (useful in B12 responsive forms of methylmalonic acidemias)

Thiamine 300 mg/day (useful in Thiamine-responsive variants of MSUD).

If hyperammonemia is present, treat as above.

Congenital lactic acidosis Supportive care: hydration, treatment of sepsis,

seizures, ventilation. Avoid sodium valproate.

Treat acidosis: sodium bicarbonate 0.35-0.5mEq/kg/hr

(max 1-2mEq/kg/hr)

Thiamine: up to 300 mg/day in 4 divided doses.

Riboflavin: 100 mg/day in 4 divided doses.

co-enzyme Q: 5-15 mg/kg/day

L-carnitine: 50-100 mg/kg orally.

Refractory seizures with suspectedmetabolic etiology

Seizures despite 2 or 3 antiepileptic drugsPyridoxine 100 mg intravenously. oral 15

mg/kg/day.Despite pyridoxine.. give trial of biotin 10

mg/day and folinic acid 15 mg/day (folinic acid responsive seizures).

Rule out glucose transporter defect: measure CSF and blood glucose

Asymptomatic newborn with a History of sibling death with suspected IEM:

After baseline metabolic screen, start oral dextrose feeds (10% dextrose).

After 24 hours, repeat screen. If normal, start breast feeds. Monitor sugar, blood gases and urine ketones, blood ammonia 6 hourly.

Medium chain triglycerides (MCT oil) before starting breast feeds

After 48 hours, repeat metabolic screen. Obtain samples for TMS and urine organic acid tests.

Follow-up for the first few months

Long term treatment of IEM

Dietary treatment: phenylketonuria, maple syrup urine disease, homocystinuria, galactosemia, and glycogen storage disease Type I & III.

Special diets for PKU and MSUD are commercially available in the west can be imported.

Based on the amino acid content of some common food products available in India, a low phenylalanine diet for PKU and diet low in branched chain amino acids for MSUDcanbe made.

urea cycle disorders and organic acidurias require dietary modification (protein restriction)

Enzyme replacement therapy

ERT is now commercially available for some

lysosomal storage disorders.

Pompe’s disease (Glycogen storage disorder

Type II).

Cofactor replacement therapy

Thiamine: mitochondrial disorders thiamine responsive variants of MSUD PDH deficiency & complex I deficiency

Riboflavin: Glutaric aciduria Type I, Type II mild variants of ETF ETFDH complex I deficiency

Pyridoxine: 50% of cases of homocystinuria due to

cystathionine β-synthetase deficiency pyridoxine dependency with seizures xanthurenic aciduria primary hyperoxaluria type I Hyperornithemia with gyrate atrophy

Biotin: Biotinidase deficiency Holocarboxylase synthetase deficiency

Cobalamin: Methylmalonic academia Homocystinuria

Folinic acid: Hereditary orotic aciduria Methionine synthase deficiencyCerebral folate transporter deficiency hereditary folate malabsorptionKearns-Sayre syndrome

Prevention

• Genetic counselling and prenatal diagnosis: • Most of the IEM are single gene defects,

inherited in an autosomal recessive manner, with a 25% recurrence risk.

• The samples required are chorionic villus tissue or amniotic fluid.

Substrate or metabolite detection:Phenylketonuria Peroxisomal defects.

Enzyme assay: lysosomal storage disorders like Niemann-Pick

disease , Gaucher disease.DNA based (molecular) diagnosis:

Detection of mutation in proband/carrier parents

Neonatal screening Tandem mass spectrometry is used in some

countries for neonatal screening for IEM

Aminoacidopathies ( phenylketonuria, MSUD,

Homocystinuria, Citrullinemia, Argininosuccinic

aciduria, hepatorenal tyrosinemia) fatty acid

oxidation defects,

Organic acidemias (glutaric aciduria, propionic

acidemia, methylmalonic acidemia, isovaleric

acidemia).

The cost of this procedure is high

Test is highly sensitive, the specificity is relatively low; and there are difficulties in interpretation of abnormal test results in apparently healthy infants.

Commercially available formulations used in IEM

Pyridoxine Tab Benadon (40mg) (Nicholas Piramal), Inj Vitneurin (1 ampoule contains 50 mg pyridoxine), Tab B-long 100mg

Hydroxycobalamin (Vitamin B12) Inj Trineurosol (1000mcg/ml) (Tridoss Laboratories)

Thiamine :Tab Benalgis (75 mg) (Franco India)

Riboflavin :Tab Riboflavin (5 mg) (Shreya)

Biotin Tab Essvit (5mg, 10mg) (Ecopharma)

Carnitine Syrup L-Carnitor (5ml=500 mg), Tab L-

Carnitor (500 mg), Inj carnitor (1g/5ml) (Elder)

Folinic acid Tab Leukorin (15 mg) (Samrath)

Sodium Benzoate Satchet 20g (Hesh Co.)

Arginine ARG-9 Satchet (3g) (Noveau Medicament)

Coenzyme Q Tab CoQ 30 mg, 50 mg. (Universal

Medicare)

Thank you