Fukuyama congenital muscular dystrophy.
Incidence
Transmitted as an autosomal recessive trait. Parental consanguinity was present in some cases. Fukuyama congenital muscular dystrophy is endemic in Japan where it is the most common form of muscular dystrophy after Duchenne muscular dystrophy. Most, if not all, previously reported cases of Fukuyama congenital muscular dystrophy outside Japan do not appear to have mutations in the fukutin gene. In Japan, FCMD is fairly common. It is approximately 50% as common as Duchenne muscular dystrophy. The estimated incidence is about 7-12 cases per 100,000 children.
Clinical Characteristics
The classical picture is the combination of generalized muscle weakness, severe brain involvement with mental retardation, frequent occurrence of seizures, and abnormal eye function. Onset is often in utero with poor fetal movements although severe arthrogryposis is rare. Most patients achieve standing with support and may be able to take a few steps with support between the age of 2 and 8 years. Progressive weakness then develops, and respiratory failure in the middle-to-late teens is an invariable complication. Enlargement of the calves, quadriceps muscles, and tongue is common. Severe weakness is usually combined with profound mental retardation. These patients typically do not speak meaningful words, although most learn to speak short sentences and may even learn to read and write a few characters. Brain MRI shows fronto-parietal polymicrogyria and, more rarely, hemispheric fusion or obstructive hydrocephalus. The cerebellum shows cystic lesions under the cerebellar cortex containing granular cells and mesenchymal tissue. In addition, MRI typically shows a transient delay of myelination that tends to gradually diminish with age. Most patients develop seizures before age 3 years. About 50% of the classical Fukuyama congenital muscular dystrophy cases show signs of ocular involvement ranging from abnormal eye movements, poor visual pursuit, and strabismus to severe myopia or hyperopia or cataracts. It is due to defects of glycosyltransferases (dystroglycanopathies). The gene responsible for Fukuyama congenital muscular dystrophy is the fukutin gene.
Precipitants
The usual precautions that should be observed for all patients with a muscular dystrophy and elevated serum CK should be followed.
Provocation Tests
None
Diagnostic Procedures
Brain MRI and ophthalmological examination will help to recognize the typical associated features. Serum CK levels are typically elevated (more than 10 times normal values). The muscle biopsy will show reduced or absent alpha-dystroglycan using antibodies that recognize a glycosylated epitope. Mutation analysis of the fukutin gene will confirm the diagnosis.