Congenital genetic inborn errors of metabolism presenting as an adult or persisting into adulthood: neuroimaging in the more common or recognizable disorders.
[phenylketonuria]
Numerous congenital-genetic inborn errors of metabolism (CIEMs) have been identified and characterized in detail within recent decades, with promising therapeutic options. Neuroimaging is becoming increasingly utilized in earlier stages of CIEMs, and even in asymptomatic relatives of patients with a CIEM, so as to monitor disease progress and treatment response. This review attempts to summarize in a concise fashion the neuroimaging findings of various CIEMs that may present in adulthood, as well as those that may persist into adulthood, whether because of beneficial therapy or a delay in diagnosis. Notably, some of these disorders have neuroimaging findings that differ from their classic infantile or early childhood forms, whereas others are identical to their early pediatric forms. The focus of this review is their appearance on routine magnetic resonance imaging sequences, with some basic attention to the findings of such CIEMs on specialized neuroimaging, based on recent or preliminary research. The general classes of disorders covered in this complex review are: peroxisomal disorders (adrenoleukodystrophy), lysosomal storage disorders (including metachromatic leukodystrophy, Krabbe or globoid cell leukodystrophy, Fabry, Niemann-Pick, GM1, GM2, Gaucher, mucopolysaccharidoses, and Salla diseases), mitochondrial disorders (including mitochondrial encephalomyopathy with lactic acidosis and strokelike episodes, myoclonic epilepsy with ragged red fibers, Leigh disease, and Kearns-Sayre syndrome), urea cycle disorders, several organic acidemias (including phenylketonuria, maple syrup urine disease, 3-hydroxy-3-methylglutaryl colyase deficiency, glutaric acidurias, methylmalonic academia, proprionic academia, 3-methylglucatonic aciduria, and 2-hydroxyglutaric acidurias), cytoskeletal or transporter molecule defects (including Alexander or fibrinoid leukodystrophy, proteolipid protein-1 defect or Pelizaeus Merzbacher, Wilson, and Huntington diseases), and several neurodegenerative disorders of brain iron accumulation. Additionally, an arbitrary "miscellaneous" category of 5 recognizable disorders that may present in or persist into adulthood is summarized, which include megalencephalic leukoencephalopathy with subcortical cysts (megancephalic leukoencephalopathy with subcortical cysts or van der Knaap disease), polymerase-III gene defect ("4H syndrome"), childhood ataxia with central nervous system hypomyelination ("vanishing white matter disease"), striopallidodentate calcinosis ("Fahr disease"), and Cockayne syndrome.
