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In two sibs antenatal ultrasonography revealed identical intracranial calcification, ventricular widening and microcephaly. The first pregnancy was artificially terminated at 19 weeks. Post-mortem examination of the brain revealed destructive calcification and extracerebral neuronal heterotopia. The second sib went to term but died 48 h after birth from irreversible lactic acidosis. Autopsy showed extensive encephalopathy with cavitation and calcification in the cerebral hemispheres, polymicrogyria, multiple neuronal heterotopia, partial callosal dysgenesis, and severe Leigh syndrome, together forming a continuum of early and late brain disruption. Mitochondrial respiratory chain abnormalities, mainly affecting complexes I and IV, and deficiency of pyruvate dehydrogenase complex were detected in skeletal muscle and in liver. A normal functioning of the respiratory chain was found in the fibroblasts. Analysis of mtDNA from muscle, liver and blood revealed normal amounts of intact mtDNA without any of the known point mutations associated with MELAS, MERRF or Leigh syndromes. The early fetal disruption and necrotic changes in the brains of sibs indicate a specific genetically determined disorder which affects neuronal migration, a finding not previously associated with respiratory chain disorders. The present disorder may mimic antenatal congenital infectious encephalopathy because of the combined finding of microcephaly and destructive intracerebral calcification. [ABSTRACT FROM AUTHOR]