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Congenital muscular dystrophy, Fukuyama type
Fukuyama type muscular dystrophy (FCMD) is a congenital progressive muscular dystrophy characterized by brain malformation (cobblestone lissencephaly), dystrophic changes in skeletal muscle, severe intellectual deficit, epilepsy and motor impairment.
The disease has a high prevalence in the Japanese population and is extremely uncommon elsewhere. The annual incidence of FCMD in Japan is estimated at 1-2/50,000 live births.
Disease onset typically occurs in early infancy. Initial symptoms include a poor suck, weak cry, floppiness and developmental delay. Symmetrical generalized muscle weakness and hypotonia are present. Patients have contractures of the hips, knees and interphalangeal joints. Later features include myopathic facial appearance, pseudohypertrophy of the calves and forearms, and ophthalmologic abnormalities (visual impairment and retinal dysplasia). Progressive cardiac involvement, and swallowing and feeding disturbances (leading to recurrent aspiration pneumonia and death) occur in infants with severe FCMD and in patients over ten years of age. Seizures (generalized tonic-clonic convulsions, complex partial seizures and partial seizures with secondary generalization, infantile spasms, tonic seizures and myoclonic seizures) occur in over 50% of affected individuals (median age of seizure onset 1-3 years of age). All patients have severe intellectual deficit and the intelligence quotient (IQ) is usually between 30 and 60.
It is caused by mutations in the fukutin gene (FKTN; 9q31-q33).
The diagnosis is based on the clinical picture, characteristic neuroimaging and electromyography findings, muscle biopsy results, and molecular genetic testing.
Differential diagnoses include Duchenne and Becker muscular dystrophies, and other muscular dystrophies associating a type II lissencephaly (known as dystroglycanopathies; see these terms). Brain, cerebellar and ocular abnormalities observed in most FCMD patients are similar to and would be diagnosed out of Japan as MEB syndrome (see this term). Therefore, there is an increasing tendency to use the global term MEB/FCMD syndrome.
Prenatal testing is possible by analysis of DNA extracted from fetal cells obtained by amniocentesis (usually performed at about 15-18 weeks' gestation) or by chorionic villus sampling (at about ten to 12 weeks' gestation).
FCMD is inherited in an autosomal recessive manner. Genetic counseling is recommendedfor parents at risk of having a child with FCMD.
Management and treatment
Management includes physiotherapy, treatment of orthopedic, respiratory and cardiac complications, respiratory aid, and medical or surgical treatment for nutritional and gastrointestinal problems. Control of seizures requires antiepileptic drugs. Surveillance includes monitoring for respiratory and cardiac function.
Prognosis depends on the severity of complications, mainly neurologic, cardiac or respiratory.
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