Inborn Errors of Metabolism in Children

Publication: 01/02/2003  --
Last review: 28/06/2018  
Next review: 28/06/2021  
Clinical Guideline
CURRENT 
ID: 220 
Approved By:  
Copyright© Leeds Teaching Hospitals NHS Trust 2018  

 

This Clinical Guideline is intended for use by healthcare professionals within Leeds unless otherwise stated.
For healthcare professionals in other trusts, please ensure that you consult relevant local and national guidance.

Inborn Errors of Metabolism in Children

Presentation

Inborn errors of metabolism (IEM) are a group of rare disorders that may present in the new-born period. The infant may present in different ways, most of which are nonspecific.

  • Often normal at birth
  • Deterioration in first 1-2 day
  • Persistent vomiting
  • Tachypnoea
  • Poor feeding
  • Lethargy, drowsiness
  • Floppy
  • ↓conscious level→ coma
  • Seizures
  • Dysmorphic features
  • Unusual odour
  • Hydrops
  • Jaundice and bleeding tendency

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Investigation

Discuss with

  • Consultant on call
  • Biochemist on call
  • Dr. Mick Henderson (Biochemistry IEM lab tel. 66861 or 07766039208)
  • Ring IEM lab (tel. 64256) in hours to inform them of samples that were sent.

First line investigations

Blood

  • FBC
  • Blood gas
  • Urea and electrolytes, calcium, magnesium
  • Liver function tests
  • Clotting
  • CRP
  • Blood glucose
  • Plasma ammonia
  • Plasma amino acids
  • Plasma lactate
  • 4x Blood spots on neonatal screening card for acylcarnitines

Urine

  • amino and organic acids
  • mucopolysaccharides and oligosaccharides
  • ketones (dipstick)

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General Management

Follow the basic principles of resuscitation.

Airway/breathing
Infants with a depressed conscious level may hypoventilate. Hypercapnia will aggravate cerebral oedema; poor tissue oxygenation will aggravate acidosis

  • Ventilation should be introduced sooner rather than later

Circulation
Appropriate and occasionally aggressive fluid resuscitation if required to improve tissue perfusion.

  • Fluid bolus 20mls/kg sodium chloride, more may be needed.
  • Care taken in the face of poor renal function

Hypoglycaemia
Take appropriate samples when the baby is hypoglycaemic
(see separate protocol in handbook).

  • Then correct immediately with 2.5mls/kg 10% glucose i.v. bolus.

Acidosis
May need large amounts of base in IEMs with metabolic acidosis.

Maintenance Fluids

  • Stop all enteral feeds.
  • Administer high carbohydrate IV fluid to reverse tissue catabolism 150-180 ml/kg/day 12.5 or 15% glucose via a central line

Antibiotics
IEMs present with symptoms and signs similar to sepsis and in the early stages the 2 are difficult to tell apart. Some IEMs predispose the infant to sepsis.

  • Benzylpenicillin and gentamicin as per protocol

Seizures
Follow seizure protocol.

  • If intractable try pyridoxine 100mg as slow iv injection.

Carnitine
Consider giving prophylactic carnitine if acute organic acidaemia is suspected, either due to previous family history or in presence of unexplained metabolic acidosis especially if ammonia is elevated.

Contact
If further advice required contact Dr Mick Henderson (as above) or the on-call metabolic consultant at the Willinck Institute, Manchester. ( 0161 701 2137 )

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Hyperammoniaemia

Definition
>100 micromol/l in term infants
>200 micromol/l in preterm or sick infants

 

Drug treatment of hyperammonaemia

  • Sodium benzoate, sodium phenylbutyrate and arginine are all available via the on-call pharmacist.
  • They are all given as a continuous infusion and can go through one peripheral cannula.
  • These medicines are unlicensed in this age group

Sodium benzoate (1g/5ml)
Dose: 250mg/kg loading dose over 90 min
Then 250mg/kg/day as a continuous infusion

Administration: See formulary
Dilute to 20mg/ml with glucose 5% or 10%,
Give 12.5ml/kg loading dose then 0.5ml/kg/hr.

Sodium phenylbutyrate (1g/5ml)
Dose: 250mg/kg/day as continuous infusion, no loading dose.

Administration: See formulary
Dilute to 20mg/ml with glucose 5% or 10%,
Give 0.5ml/kg/hr.

Arginine (20% solution)
Dose: 200 mg/kg loading dose over 90 min.
Then 200 mg/kg/day as continuous infusion.

Administration: See formulary
Dilute to 20mg/ml with glucose 5% or 10%,
Give 10ml/kg loading dose then 0.4ml/kg/hr.

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Samples to Obtain from a Dying Child with a Suspected IEM

Parental consent should be obtained before taking the samples.
Investigation of Suspected Inborn Errors of Metabolism in Dying Babies

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Provenance

Record: 220
Objective:

This guideline is aimed at the immediate investigation and management of an infant presenting with a suspected inborn error of metabolism.

Clinical condition:
Target patient group:
Target professional group(s): Secondary Care Doctors
Secondary Care Nurses
Adapted from:

N/A


Evidence base

  1. Burton BK. Inborn errors of metabolism in Infancy: A guide to diagnosis. Pediatrics 1998:102;69
  2. Champion M, Fox G.Inborn Errors of Metabolism: A guide for Neonatologists. Pub. Orphan Europe.
  3. Wraith E. Inborn Errors of Metabolism in the neonate in Textbook of Neonatology. Ed. Rennie JM & Roberton NRC. 3rd Ed. Churchill Livingstone 1999.

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Document history

LHP version 1.0

Related information

Additional information can be found on:
1. The National Metabolic Biochemistry Network http://www.metbio.net or
2. The British Inherited Metabolic Diseases Group guidelines http://www.bimdg.org.uk/site/guidelines.asp which are regularly reviewed by top UK clinicians and dieticians

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