Infantile fibre type disproportion, myofibrillar lysis and cardiomyopathy: a disorder in three unrelated Dutch families.

An apparently new cardioskeletal myopathy is reported in three unrelated families. Five infants were affected by rapidly progressive generalized muscle weakness, with onset shortly after birth, and dilated cardiomyopathy. All had generalized tremor (clonus) starting in the first week of life. The disease was lethal in all cases between 4 and 6 months. Muscle biopsy, performed in four of the five patients, showed a light microscopic pattern of small type I and normal-sized type II fibres. By electron microscopy small fibres were affected by myofibrillar disruption and swelling of organelles. Findings in blood and urine suggested a disturbance in energy metabolism but an extensive search for respiratory chain disorders and disorders of mitochondrial fatty acid oxidation in frozen muscle and cultured fibroblasts was negative. The findings support a new progressive autosomal recessive infantile cardioskeletal myopathy in which type I muscle fibres are preferentially affected.