Genetic disorders of mitochondrial function

Magnetic resonance of metabolic and degenerative diseases in children

Cerebral magnetic resonance imaging and spectroscopy form an integral part in the diagnosis and management of the vast spectrum of metabolic and degenerative disorders in children. These varied disorders have been classified in many different ways, according to anatomic location, head size, enzyme disorder, or cellular morphology and function. The clinical features and magnetic resonance imaging appearances of the most common disorders are discussed.

The cyclic dilemma: organic, functional, and environmental interaction in a young teenager

This Grand Rounds considers an early-adolescent female who demonstrated a mixed clinical picture including rapid cycling of psychotic behavior. The case presents issues commonly faced in hospital practice and provides an example of the use of standardized instruments in assessment and monitoring treatment, as well as a discussion of issues germane to inpatient child and adolescent psychiatrists and related treatment team members.

Sensorineural deafness inherited as a tissue specific mitochondrial disorder

We present here a large Israeli-Arab kindred with hereditary deafness. In this family 55 deaf subjects (29M, 26F), who are otherwise healthy, have been identified and traced back five generations to one common female ancestor. The deafness is progressive in nature, usually presenting in infancy and childhood. Audiometry on six deaf and seven unaffected subjects was consistent with severe to profound sensorineural hearing loss. Based on formal family segregation analysis, the inheritance of deafness in this family closely fits the expectation of a two locus model owing to the simultaneous mutation of a mitochondrial gene and an autosomal recessive gene. Thus, this disorder appears to have the unusual features of being an inherited tissue specific mitochondrial disease and apparently requiring the homozygous presence of a nuclear gene for clinical expression. Most importantly, this disorder presents a unique opportunity to investigate the molecular basis of hereditary non-syndromic deafness and normal hearing.

Infant-onset progressive myoclonus epilepsy

We report the clinical, electroencephalographic, neurophysiologic, and neuroimaging findings in eight children with infant-onset progressive myoclonus epilepsy, all of whom had muscle biopsies performed as as part of the diagnostic evaluation. Each child had myoclonic seizures, generalized tonic-clonic seizures, and neurologic regression or marked developmental delay. Four children died before 3 years of age. Electroencephalograms in seven children showed an abnormally slow background with bilateral multifocal paroxysmal discharges but no burst suppression pattern or photoparoxysmal response. Muscle biopsy specimens were submitted for histopathology and respiratory-chain enzyme studies. Nonspecific abnormalities on light microscopy or electron microscopy were found in seven samples, including increased subsarcolemmal deposits of mitochondria or morphologic mitochondrial changes, but no ragged-red fibers were seen. Respiratory-chain enzyme studies were performed on five samples and in three children (all of whom had a history of elevated lactate in serum or cerebrospinal fluid), there were low levels of rotenone-sensitive reduced nicotinamide adenine dinucleotide (NADH) cytochrome c reductase characteristic of a defect in the complex I part of the respiratory-chain pathway. This study has shown that infant-onset progressive myoclonus epilepsy can be distinguished from other myoclonic epilepsy syndromes of infancy by clinical and electrographic features. Furthermore, respiratory-chain enzyme defects are a relatively common cause of infant-onset progressive myoclonus epilepsy. The absence of ragged-red fibers on muscle histopathology does not preclude a mitochondrial enzyme abnormality.

de Toni-Fanconi-Debré syndrome with Leigh syndrome revealing severe muscle cytochrome c oxidase deficiency

We describe a patient with severe muscle cytochrome c oxidase deficiency who had de Toni-Fanconi-Debré syndrome and acute neurologic deterioration resembling Leigh syndrome, without clear evidence of muscle abnormality. Metabolic investigations revealed elevated cerebrospinal fluid lactate values contrasting with normal blood lactate, and high 3-hydroxybutyrate/acetoacetate ratio with normal lactate/pyruvate ratio. This case emphasizes the importance of performing metabolic and biochemical investigations in every patient with Leigh syndrome, even in the absence of hyperlactatemia or myopathy.