Table 1.

Specialised investigations reported in the 225 undiagnosed cases during life, in addition to extensive biochemical studies of blood and urine

Investigation	Cases (n)
MRI brain scans	184
Electroencephalogram	159
Cerebrospinal fluid examination	115 (85 for lactate level)
White cell lysosomal enzyme study	89
Electroretinogram±visual evoked potentials	74
CT brain scans	65
DNA studies for known mutations	49 (23 of these for known mitochondrial disorders)
Muscle biopsy	46
Skin biopsy (often for culture of skin fibroblasts)	31
Nerve conduction study±electromyography	27
Chromosomes	18
Bone marrow for histology	6
Rectal biopsy	5
Brain biopsy	3
Conjunctival biopsy	2
Liver biopsy	1