Abnormalities of the nuclear envelope in porcine muscle affected with congenital myofibrillar hypoplasia.

The nuclear ultrastructure of muscle fibres in congenital myofibrillar hypoplasia of piglets was studied in order to provide more information on the pathological changes present. In the initial stages of the disease, muscle fibres with a small reduction of myofibrils often had an increased number of nuclear pores. In the more advanced stages of the disease, the following nuclear abnormalities were observed in muscle fibres showing an extensive disintegration of myofibrils: 1) large dilations of the perinuclear cisternae, 2) small nuclear protrusions projecting into these dilations and 3) appositions of stray membranes of the disrupted endoplasmic reticulum to the nuclear envelope. The increase in the number of nuclear pores may be significant in the development of pathological changes in congenital myofibrillar hypoplasia which is thought to be a hereditary disease. The observed abnormalities of the nuclear envelope appear to be characteristic for muscle fibres undergoing degeneration.