Case Scenario:

• 15 year old girl presented in ED with

aggressive behaviour and hallucinations.

• No associated fever, vomiting, seizures

or developmental concerns

• Previously well

Inborn Errors of Metabolism

Clinical Approach to Diagnosis

and Treatment

Joy Lee, M.D., FRACP

Acknowledgement

Asso. Prof. Avihu Boneh for the slides he

shared

Misconceptions on Inborn Errors of Metabolism

• IEMs are very RARE.

• These disorders are difficult to DIAGNOSE and to

TREAT.

STRESS TEST ...

Outline

Part I

Overview of IEM

When to suspect IEM?

What investigations to request?

What is expanded newborn screening?

Part II

What are the treatment principles?

Overview of IEM

Incidence - Prevalence

Individually very rare

Collectively ~1; 5000

Patterns of Inheritance

MENDELIAN

~60% autosomal

recessive

~20% autosomal

dominant

~15% X-linked

(Scriver, et al. 2001)

COMPLEX NON-

MENDELIAN

~5% mitochondrial

Classification

According to intracellular site

ex. mitochondrial disorders, peroxisomal disorders

lysosomal storage disorders

According to biochemical pathology

ex. disorders in intermediary metabolism

disorders of neurotransmitter metabolism

disorders of purines/pyrimidines

Disorders of Intermediary Metabolism

Defects in Carbohydrate Metabolism

ex. Galactosaemia, GSD, HFI

Defects in Protein Metabolism

ex. Amino Acidopathies (MSUD)

Organic Acidurias (MMA, PA, IVA, GAI)

Urea Cycle defects

Defects in Fatty Acid and Ketone

Metabolism

ex. Fatty Acid Oxidation Defects

Defects in Energy Metabolism

ex. PDH deficiency

mitochondrial respiratory chain disorders

A B C

General Metabolic Concept

Enzyme + Co-factor

D

3 Sources of Diagnostic Confusion

Confusion with common acquired

conditions ex. sepsis

Confusion caused by association with

intercurrent illness

Confusion arising from genetic

heterogeneity ex. MPS

Clarke, A Clinical Guide to Inherited Metabolic diseases

3rd edition

MPS I - Spectrum

Disease progression: severe MPS I

10 months 12 months

22 months 34 months

39 months

Muenzer J. The mucopolysaccharidoses: A heterogeneous group of disorders with variable pediatric presentations. J Peds. 2004. S27 – S34.

Photos courtesy of US MPS Society

When to suspect IEM?

1) Good history taking

2) Physical examination including review

of systems

History

Pregnancy and Birth: HELLP syndrome, maternal diet, foetal

movements , prolonged jaundice

Family: Ethnic origin, consanguinity, unexplained

deaths/miscarriages (? sex), SIDS, unexplained MR in sibling/close

relative, other affected sibs

Present and Past: Recurrent unexplained symptoms ex. vomiting,

respiratory and ear infections, progressive CNS degeneration, MR in

absence of major congenital anomalies, recurrent surgeries ,

surgical procedures (recovery from Anaesthesia)

History

Dietary:

aversion to certain food such as protein

vegetarian diet

craving for certain food

Clinical Presentation of IEM

Variable age of onset and clinical symptoms

Neurologic

a) acute encephalopathy

b) chronic encephalopathy

psychomotor retardation, regression,

seizures, movement disorders, stroke,

ataxia, psychiatric, myopathy

Hoffman et al Inherited Metabolic Diseases A Clinical Approach

Clinical Presentation of IEM

Variable age of onset and clinical symptoms

Neurologic

a) acute encephalopathy

b) chronic encephalopathy

psychomotor retardation, regression,

seizures, movement disorders, stroke,

ataxia, psychiatric, myopathy

Clinical Symptoms of IEM

Acute encephalopathy

Vomiting (recurrent)

Feeding refusal

breathing problems

Lethargy / irritability

Floppiness /dystonia/weakness/ataxia

Seizures

…in relation to age, precipitating factors

Clarke, A Clinical Guide to Inherited Metabolic diseases

3rd edition

Disorders of Intermediary Metabolism

Defects in Carbohydrate Metabolism

ex. Galactosaemia, GSD, HFI

Defects in Protein Metabolism

ex. Amino Acidopathies (MSUD)

Organic Acidurias (MMA, PA, IVA, GAI)

Urea Cycle defects

Defects in Fatty Acid and Ketone

Metabolism

ex. Fatty Acid Oxidation Defects

Defects in Energy Metabolism

ex. PDH deficiency

mitochondrial respiratory chain disorders

Precipitating Factors

Feeding / fasting

Dietary overload (e.g. protein)

Dietary deficiency (e.g. vit. B6, B12, carnitine)

Intercurrent infection / fever

Surgery

Exercise

Specific toxins (e.g. valproic acid)

Clinical Presentation of IEM

Neurologic – chronic encephalopathy, movement disorder,

diurnal pattern, ataxia, muscle pain, abnormal tone

Hepatic – jaundice, liver failure, hypoglycaemia

Cardiac – cardiomyopathy, rhythm disturbances

Respiratory – sleep apnoea, recurrent chest infections

Renal – tubular dysfunction, renal stones

Eye – cataracts, optic atrophy, retinal abnormalities

Dermatological – alopecia, rash, “kinky hair”,

Ears – recurrent infections, hearing loss

Gastrointestinal – chronic diarrhoea

Growth - failure to thrive

Dysmorphism

IEM and Dysmorphism

Disorders of cholesterol biosynthesis - SLO

Peroxisomal disorders

Mitochondrial disorders

Lysosomal disorders (ex. MPS)

CDG syndromes

Glutaric aciduria type II

Atlas of Inherited metabolic diseases 3rd edition

Clinical Clues

Some characteristics of psychomotor retardation that should

“alert” clinicians.

1) It tends to be global affecting all spheres of development

to some extent.

2) Severe irritability, impulsitivity/aggressiveness, hyperactivity and

nocturnal restlessness are more common among patients with MR

caused by IEM than non-metabolic.

Clarke, A Clinical Guide to Inherited Metabolic diseases

3rd edition

Clinical Clues

Some characteristics of psychomotor retardation that

should “alert” clinicians.

3) Psychomotor retardation is usually progressive – gap wider

with time when compared with other children.

4) Psychomotor retardation is usually asso. with other objective

evidence of neurologic dysfunction – abnormal tone, impairment

of senses, seizures, pyramidal tract signs, cranial nerve deficits.

Clarke, A Clinical Guide to Inherited Metabolic diseases

3rd edition

Clinical Clues:

Physical Examination

Multisystem involvement:

review of systems is important!

Pattern of abnormalities – typical of certain disorders

ex. Kinky hair, laxity of joints/skin, developmental delay

Pattern and degree of involvement of other organs and

tissues

ex. Coarse features, hepatosplenomegaly, joint contractures,

umbilical hernias, obstructive sleep apnoea

Unusual smell – ex. fishy odour, sweaty feet

Nyhan et al Atlas of Inherited Metabolic Diseases 3rd ed

Nyhan et al Atlas of Inherited Metabolic Diseases 3rd ed

Nyhan et al Atlas of Inherited Metabolic Diseases 3rd ed

Nyhan et al Atlas of Inherited Metabolic Diseases 3rd ed

Nyhan et al Atlas of Inherited Metabolic Diseases 3rd ed

Nyhan et al Atlas of Inherited Metabolic Diseases 3rd ed

Nyhan et al Atlas of Inherited Metabolic Diseases 3rd ed

What investigations to request?

Laboratory Tests (1)

Acid-Base / Electrolytes

Glucose

Lactate

Ammonia

Urine ketones

Calculate for Anion Gap – normal < 16

Results in 30 minutes

or less!

Questions you should ask yourself

Is there Metabolic Acidosis?

Is there Hypoglycaemia?

Is there Ketosis?

Is there Hyperammonaemia?

Clarke, A Clinical Guide to Inherited Metabolic diseases, 3rd edition

Table 3: Interpretation of Results1

Metabolic Condition Glucose Lactate Metabolic Acidosis Ammonia Anion Gap3 Urine ketones

Mitochondrial disorder N usually very high present N increase negative

MSUD low or N N variably present N may be increase strongly +++ OA low or N may be high very acidotic may be high usually increase positive FAOD low or N may be high variably present may be high may be increase neg or low2

UCD N N N high N negative 1 Serves as a guide. Secondary factors (dehydration/poor perfusion/sepsis) can affect interpretation. 2Inappropriately low 3Compute by using Na - (Chloride + Bicarbonate). Normal < 16 mmol/L N - normal

Laboratory Tests – Blood (2)

Biochemical

Plasma amino acids

Guthrie card amino acids/acylcarnitine profile

Plasma carnitine

Ketones, free fatty acids

Pyruvate – needs special tube

Ancillary:

Full blood count – ex. Neutropenia, pancytopenia

LFT, coagulation screen, alpha feto protein

Lipid profile, uric acid

Creatine kinase

Blood Spots on Guthrie Card

for a rapid analysis of : acylcarnitines

amino acids

DNA extraction for mutation analysis

Dry in room air; store/send in a paper envelope

Laboratory Tests: Urine

Smell

pH

Glucose

Ketones

Protein

Reducing Substances (Clinitest, Clinistix)

Laboratory Tests: Urine

Amino Acids

Organic Acids

GAGs

Others: Sulphocysteine, Purines and

Pyrimidines, Bile acids, P6C

Store and freeze extra urine for further

analysis

Laboratory Tests - CSF

Glucose

Protein

Lactate

Pyruvate

Amino Acids

Neurotransmitters – special tubes

*Paired: Blood/CSF – glucose, lactate,

pyruvate and amino acids*

Store and freeze extra sample for further analysis

Sample Handling/Collection

Blood

ammonia – free flowing, in ice, send to lab ASAP

lactate – free flowing, no tourniquet

Do not freeze whole blood.

Separate plasma/serum and freeze at -20 C or -70 C

Urine: Freeze at -20 C or -70 C

CSF:

A bloody sample is not informative

If only a few RBC: spin and freeze at -20 C or -70 C.

Post-Mortem Samples

Collect and freeze plasma, urine and CSF

Blood spots on Guthrie Card

Skin biopsy: put in culture medium or sterile

Normal Saline; store at 4 C

Biopsies: Liver, heart and heart

Guidelines on PM samples on RCH website

PM kit available in core lab with instructions

How NOT to order metabolic testing

Expanded Newborn Screening

Current Australian newborn screening panels

• Congenital hypothyroidism

enzyme linked immunosorbent assay (commercial kit)

• Cystic fibrosis

ELISA or FIA (commercial kit) followed by mutation testing

• Phenylketonuria + 22 other inborn errors of metabolism

Tandem mass spectrometry

(single test --- multiple disorders)

• Galactosaemia (not in Vic)

Collection of Guthrie card at 48 to 72 hours of age

Testing is voluntary with consent >99.5% of babies have the test

Program is funded by the Victorian government ~ 74,000 Vic babies tested per year (2011)

~ 77,400 babies in 2012

Sorting the cards

Punching out Microtitre plate

Tandem mass spectrometry test Hypothyroidism ELISA test

Adding reagents

Amino acids

Amino acid Metabolic Possibilities

Phe PKU, hyperphe, BH4 metabolism defect

Valine, xleu Classic MSUD

Glycine NKH

Methionine Homocystinuria, MAT deficiency

ASA Argininosuccinic aciduria

Citrulline Citrillunemia I or II

Tyrosine Tyrosinemia I , Tyrosinemia II or III

Acylcarnitines

Acylcarnitine Metabolic Possibilities

Free carnitine(C0) Carnitine uptake defect

Propionylcarnitine(C3) MMA, PA, cobalamin defect, B12 def.

Octanoylcarnitine(C8) MCAD deficiency

Glutarylcarnitine(C5DC) GAI

Tetra-decanoylcarnitine(C14) VLCAD deficiency

3-hydroxy-isovalerylcarnitine (0HC5) holocarboxylase def., MCCC def.

Normal newborn profile

-5

-4

-3

-2

-1

0

1

2

3

4

5

GU

AN

IDIN

OA

CE

TIC

OH

PR

OL

INE

D5 P

HE

(IN

T S

TD

)

GL

Y

AL

A

VA

L

ISO

LE

U_L

EU

_O

HP

RO

OR

N

LY

S_G

LN

ME

T

PH

E

GL

YC

YL

-PR

OL

INE

AR

G

CIT

RU

LL

INE

TY

R

HO

MO

CIT

RU

LL

INE

AR

GIN

INO

SU

CC

INIC

C8 C

AR

N (

INT

ST

D)

D9F

C_U

ND

ER

IV

FR

EE

CA

RN

C2 C

AR

N

C3 C

AR

N

C4 C

AR

N

C5:1

CA

RN

C5 C

AR

N

OH

C4 C

AR

N

C6 C

AR

N

OH

C5 C

AR

N

C8 C

AR

N

C3 D

C C

AR

N

C10 C

AR

N

C5 D

C C

AR

N

C12 C

AR

N_C

6:1

DC

C6 D

C C

AR

N

OH

C5 D

C C

AR

N

C14:1

CA

RN

C14 C

AR

N

C16 C

AR

N

OH

C16 C

AR

N

C18 C

AR

N

OH

C18:1

CA

RN

C0/(

C16+C

18)

-10 = LOW (undetected with lower cutoff>0)

<-1 = LOW (divisors of lower cutoff)

-1 to 0 = NORMAL (between lower cutoff and median)

0 to 1 = NORMAL (between median and cutoff)

>1 = HIGH (multiples of cutoff)D:\Newborn\Mar2004\02.PRO\Data\A27247-AA-1Select sample:

Newborn screening MSMS panel example (a)

C8 and C6 carnitine, supported by C8/C10 ratio

• Almost diagnostic for medium chain acyl CoA dehydrogenase deficiency

Amino acids acyl carnitines ratios

What conditions are detected by tandem mass spectrometry?

Group A: potentially or often serious, well detected PKU, homocystinuria, tyrosinemia II Citrullinemia type I, argininosuccinic aciduria, classic MSUD methylmalonic acidaemias, isovaleric acidaemia, propionic acidemia GAI, multiple carboxylase def. medium-chain acyl CoA dehydrogenase (MCADD), LCHAD, CPT I or II Carnitine transport defect

Group B: less serious

3-methylcrotonyl CoA carboxylase

2-methylbutyryl CoA dehydrogenase Short-chain acyl CoA dehydrogenase

Group C: potentially or often serious, poorly detected Tyrosinaemia type 1, Citrullinemia II

OTC deficiency, argininaemia Glycine encephalopathy, cobalamin C def.

What conditions are detected by tandem mass spectrometry?

Group D: maternal disorders vitamin B12 deficiency

3-methylcrotonyl CoA carboxylase deficiency Carnitine uptake defect

Finally…

‘Think Metabolic’

Do ‘the basics’

Call for assistance