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Inborn errors of metabolism (Clinical presentation (Dysmorphic features,…
Inborn errors
of metabolism
Epidemiology
Usually AR inheritance
Individually rare,
collectively common
Definition
Disorders of enzyme reactions
involved in synthesis, conversion
or degradation of molecules
Screening
Newborn blood tests
CF, haemaglobinopathies, hypothyroidism,
6 IEMs (PKU, MCAD, MSUD,
GA1, isvoleric acidemia, homocysteinuria)
Management
Medical
Symptomatic
AEDs
Analgesia
Enzyme replacement
E.g.
Specific
Ammonia scavangers
Conservative
Information, advice, support
Low protein diet (IA, homocyst, MSUD)
Phenylalanine restriction (PKU)
Special diet and avoid fasting (MCAD, GA1)
Diagnosis
History
SH
Living arrangements, nursery/school,
social support
FH
Any IEMs
PC/HPC
Non-specific e.g. dysmorphism, developmental delay,
faltering growth, seizures, unexplained acidosis/alkalosis
PMH
Growth and development
Known medical conditions
Newborn screening results
DH
Meds, allergies
Investigations
Urine
Metabolic screen (AAs, organic acids, GAGs)
Bedside
Obs
Bloods
ABG (acidosis if excess organic acid alkalosis), FBC, U+E, LFT
(may be deranged), glucose (may have hypos)
Metabolic screen (AAs, ammonia, FAs, white cell enzymes, lactate)
Genetic screen
Examination
Cardio exam
Displaced apex (cardiomegaly)
Developmental exam
Regression/loss of skills
Developmental delay
Neuro exam
Seizures, reduced IQ
Drowsiness, irritability, coma
Abdo exam
Hepatosplenomegaly
Clinical
presentation
Dysmorphic features
Developmental regression
Seizures
Faltering growth
Pathophysiology
Toxic metabolites
Accumulation o f a metabolite
Amino acids e.g. homocysteinuria
Urea cycle e.g. citrullinemia
Organic acids e.g. isovaleric acidemia
Carbs e.g. galactosaemia
Organelle disorder
Lysosomes (mucopolysaccharidoses) e.g. Hurler, Hunter, Sanfillipo, Morquio, Maroteaux-Lamy
Peroxisomes e.g. Zellweger syndrome
Energy metabolism
Mitochondrial diseses e.g. MELAS, MERRF, Alpers
Fatty acid oxidation e.g. carnitine transporter deficiency
Glycogen storage diseases e.g. McArdle disease
Lipid metabolism e.g. familial hypercholesterolemia, Fabry, Gaucher,
Niemen-Pick type C, Wolman disease