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Metabolic syndromes: neurological
There are 7 presentations of IMD with neurological features.
Developmental delay is a common problem, but the features that warrant investigation for IMD include:
• Global delay affecting all areas of development.
• Progressive course with loss of developmental milestones.
• Objective evidence of neurological dysfunction (e.g. special senses, pyramidal tract, extrapyramidal, cranial nerves).
• Severe behaviours including irritability, impulsiveness, aggressiveness, and hyperactivity.
• Seizures (complex partial or myoclonic) originating early in life that are resistant to usual therapy.
Causes include vitamin B6 dependency; biotinidase deficiency; neuronal ceroid-lipofuscinosis; GM2 gangliosidosis; cherry-red spot–myoclonus syn-drome (sialidosis type I); Leigh disease; Alper’s disease; MELAS (mitochon-drial encephalopathy–lactic acidosis and stroke-like episodes syndrome).
• Central involvement only: Canavan disease; Alexander disease; GM2 gangliosidosis; GM1 gangliosidosis; X-linked adrenoleucodystrophy (ALD); amino acidurias, organic acidurias.
• Central and peripheral involvement: metachromatic leucodystrophy (MLD); Krabbe leucodystrophy; peroxisomal disorders.
• Muscle: mitochondrial myopathy.
• Hepatosplenomegaly +/– bone: Gaucher disease, Niemann–Pick disease, mucopolysaccharidosis (MPS) I–IV (Hurler disease, Hunter disease, Sanfilippo disease, Sly disease), GM1 gangliosidosis, sialidosis II, Zellweger.
• Skin +/– connective tissue: homocystinuria; Menkes; fucosidosis; multiple sulphatase deficiency; galactosialidosis; prolidase deficiency.
· Clinical: developmental assessment and neurological examination
• Imaging: MRI of head; X-rays of hands, chest, lateral spine
• Blood: plasma amino acids; ammonia; lactate
• Urine: amino acids, organic acids, and mucopolysaccharide and oligosaccharide screen
• Electrophysiology: auditory brainstem reflexes; visual-evoked potentials; somatosensory-evoked potentials; nerve conduction;
Deterioration in level of consciousness resulting from IMD:
• may occur in a previously healthy child;
• usually shows no focal features, but ataxia may be present;
• may start with unusual behaviour;
·progresses rapidly, even to the stage of coma.
The likely causes are: hyperammonaemia; amino aci-dopathy; organic aciduria; fatty acid oxidation defect; mitochondrial defect; hypoglycaemia.
The IMD associated with stroke or stroke-like episodes are:
• Fabry disease.
• Organic acidopathy: methylmalonic acidaemia; propionic acidaemia; isovaleric acidaemia; glutaric aciduria I and II.
• Ornithine transcarbamoylase deficiency.
• Congenital disorder of glycosylation type 1A.
• Familial hemiplegic migraine.
• Ataxia: maple syrup urine disease; pyruvate dehydrogenase deficiency; Friedreich ataxia; abetalipoproteinaemia.
• Choreoathetosis and dystonia: glutaric aciduria I; Lesch–Nyhan disease; triose phosphate isomerase deficiency.
• Parkinsonism: Wilson disease; tyrosine hydroxylase deficiency.
• Acute intermittent muscle weakness: hyperkalaemic periodic paralysis; paramyotonia congenita; hypokalaemic periodic paralysis.
·Progressive muscle weakness: glycogen storage disease II (GSD, Pompe disease); GSD III.
• Exercise intolerance with cramps and myoglobinuria: myophosphorylase deficiency, carnitine palmitoyltransferase II.
• Myopathy as a manifestation of multisystem disease: mitochondrial myopathies.
The causes include: dopamine B-hydroxylase deficiency; neurovisceral porphyrias; Fabry disease; MPS I–III; occipital horn syndrome; mitochondrial neurogastrointestinal encephalomyopathy.
The causes include the following:
• Child: MPS II; MPS III; X-linked ALD; Lesch–Nyhan syndrome.
Adolescent: late-onset MLD; late-onset GM2 gangliosidosis; porphyria; Wilson disease; Wolfram syndrome; cerebrotendinous xanthomatosis; urea cycle defect; homocystinuria; adult onset neuronal ceroid lipofuscinosis.
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