Clinical and laboratory findings in referrals for mitochondrial DNA analysis
a Neurogenetics
Section, Institute of Neurology, and Hospital for Neurology and
Neurosurgery, Queen Square, London WC1N 3BG, UK, b Institute of Child Health and Hospital for Sick
Children, Great Ormond Street, London WC1N 3JH, UK
Correspondence to: Dr Wood.
Accepted 9 February
1998
BACKGROUND
Increasingly,
mutations of mitochondrial DNA (mtDNA) are being considered when
investigating the aetiology of neurological diseases in childhood.
However, they are often difficult to predict clinically.
METHOD
Mitochondrial
DNA analysis was carried out on 190 children from 1992 to 1996. Most
patients were screened for large scale rearrangements and point
mutations at nucleotide positions 3243, 3271, 8344, and 8993.
RESULTS
Mutations were
found in only 15 patients (7.9%) and were either large scale
rearrangements (seven patients) or point mutations at nucleotide
position 3243 (eight patients). Other point mutations were screened for
depending on the clinical picture. The age of symptom onset was
significantly older in children with an mtDNA mutation (mean 7.0 years)
compared with children without a mutation (mean
2.8 years). Neither Leigh's syndrome (28 cases)
nor severe infantile lactic acidosis (12 cases) was associated with
mtDNA mutation. Only three clinical features were significantly
associated with an mtDNA mutation: progressive external
ophthalmoplegia, myopathy, and pigmentary retinopathy. Family history
was valuable: the point mutation at nucleotide 3243 (but not the large
scale rearrangements) was associated with maternal inheritance; and consanguinity was not associated with mtDNA mutations. The only investigation that provided specific evidence of an underlying mtDNA
mutation was histochemical staining of muscle biopsy specimens. The
large scale mutations associated with Kearns-Sayre syndrome and
progressive external ophthalmoplegia were found in DNA from muscle
only, not leucocyte DNA; whereas point mutations were found in
leucocyte DNA.
CONCLUSIONS
Even among
children seen at a neurogenetic referral centre, mtDNA mutations were
very uncommon. Muscle biopsy was the only investigation to provide
evidence of mtDNA abnormality.
© 1998 by Archives of Disease in Childhood
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