Dominantly inherited megalencephaly, muscle weakness, and myoliposis: a carnitine-deficient myopathy within the spectrum of the Ruvalcaba-Myhre-Smith syndrome.

We report 27 children, aged 14 months to 9 years, who had megalencephaly, hypotonia, proximal muscle weakness, speech and motor delay, and increased intracellular lipid (myoliposis) in needle muscle biopsy specimens. The patients had many features of the Ruvalcaba-Myhre-Smith syndrome, and in 17 families we confirmed the autosomal dominant inheritance pattern previously suggested. Muscle carnitine content was low in all 11 patients and all 4 affected relatives tested. All 27 probands were treated with oral L-carnitine; a clinical response was noted in 17. We speculate that myoliposis may be found in other disorders with megalencephaly and muscle symptoms. In such cases, muscle carnitine deficiency should be considered. The reason for the reduced muscle carnitine content is not known.