Fukuyama congenital muscular dystrophy
|Fukuyama congenital muscular dystrophy|
|Classification and external resources|
Fukuyama congenital muscular dystrophy (FCMD) is a rare, autosomal recessive form of muscular dystrophy (weakness and breakdown of muscular tissue) mainly described in Japan but also identified in Turkish and Ashkenazi Jewish patients. Fifteen cases were first described in 1960 by Fukuyama.
FCMD mainly affects the brain, eyes, and muscles. In particular, the disorder affects development of the skeletal muscles leading to weakness and deformed appearances, and brain development is blunted affecting cognitive functioning as well as social skills.
Fukuyama congenital muscular dystrophy is the second most prevalent form of muscular dystrophy in Japan. One out of every 90 people in Japan is a heterozygous carrier.
Fukuyama congenital muscular dystrophy is characterized by a decrease in skeletal muscle tone as well as an impairment in brain and eye development.
Initial symptoms of FCMD present in early infancy as a weak cry, decreased ability to feed, and poor muscle tone. Marked differences in facial appearance occur due to decreased muscle tone. These include drooping eyelids and an partially open mouth. The axial and appendicular muscles become atrophied, which causes difficulty developing motor skills including standing, sitting, and walking. For most of these children, the maximum motor function they will ever obtain will be sitting upright on their buttocks and sliding. The majority of children with FCMD will never walk. Seizures are also common in children with FCMD occurring in over fifty percent of afflicted children. Myocardium can also be affected by FCMD. After 10 years of age, children with FCMD develop continually worsening heart problems. Swallowing (peristalsis) may also be affected. Specific skeletal abnormalities include contractures and kyphoscoliosis.
In addition to the muscular abnormalities, Fukuyama congenital muscular dystrophy also affects the nervous system and various associated parts. FCMD affects normal development of the brain producing a broadly smooth, bumpy shaped cortex named cobblestone lissencephaly as well as various other malformations, notably micropolygyria. These children also experience delayed myelination in the brain. Because of the abnormal physical development of the brain, children affected by FCMD develop motor and speech functioning much more slowly. The also have impaired intellectual capabilities including mental retardation. Children with FCMD may also experience atypical optic features including decreased visual capabilities.
Cause and Genetics
The FKTN gene, located at human chromosome 9q31, codes for the protein fukutin. Mutations in this gene, and therefore the fukutin protein, are the cause of FCMD. The disease is inherited in an autosomal recessive manner. This means the defective gene responsible for the disorder is located on an autosome (chromosome 9 is an autosome), and two copies of the defective gene (one inherited from each parent) are required in order to be born with the disorder. The parents of an individual with an autosomal recessive disorder both carry one copy of the defective gene but usually do not experience any signs or symptoms of the disorder.
A mutation in the FKTN gene results in a malformed fukutin protein. Fukutin's function in development is uncertain, but it is proposed that fukutin modifies the alpha-dystroglycan protein, which is important in anchoring cells to certain molecules, specifically including some proteins. Alpha-dystroglycan in skeletal muscles helps to prevent the breakdown of muscle fibers through stabilization and protection. Alpha-dystroglycan also helps brain development by assisting in the migration of neurons.
Most frequently, FKTN is mutated in such a way that creates a shortage of fukutin in the cell, which in turn creates problems during formation of alpha-dystroglycan leading to less stabilization of muscle cells. Use of the destabilized muscle fibers over time causes them to break down and a gradual decline in muscle tone and atrophy of muscle fibers occurs. The decline in cerebral fukutin causes neuronal cells to continue moving beyond their intended destination and sometimes outside of the brain. Researchers[who?] believe this migration of neuronal cells outside of the brain causes the cobblestone lissencephaly.
Presence of the symptoms stated above indicates Fukuyama congenital muscular dystrophy. These include:
- Decreased muscle tone in infancy and contractures in the lower limbs and the toes.
- Below average motor and speech skills
- Abnormal facial features including a partially open mouth and drooping eyes
- Family history of FCMD
- MRI indicating cobblestone lissencephaly including smooth, broadly bumped surface, indications of delayed mielination, and enlarged lateral ventricles
Serum creatine kinase concentration and muscle biopsies can also be obtained to help determine a FMCD diagnosis. FKTN molecular genetic testing is used to determine a mutation in the FKTN gene after an serum creatine kinase concentration, muscle biopsies, and/or MRI imaging have presented abnormalities indicative of FCMD.
There is no cure for Fukuyama congenital muscular dystrophy at this time and no definitive treatment exists. Treatment offers preventative tactics to delay muscle breakdown and increase life expectancy. Stretching and physical therapy can increase mobility. Treatment also includes correcting skeletal abnormalities such as kyphoscoliosis through orthopedic surgery and other orthopedic techniques. Antiepileptic medication is administered to help prevent seizures. ACE inhibitors and beta blockers help treat heart conditions.
Fukuyama congenital muscular dystrophy has a rather bleak prognosis. Most children with FCMD reach a maximum mobility at sitting upright and sliding on their buttocks. The compounded effects of continually worsening heart problems, impaired mental development, problems swallowing, and additional complications, children with FCMD rarely live through adolescence and die before the age of 20.
- Online 'Mendelian Inheritance in Man' (OMIM) 253800
- "Congenital Myopathies and Weaknesses". Washington University, St Louis, MO. Retrieved 29 November 2012.
- Fukuyama Y, Kawazura M, Haruna, H (1960). "A peculiar form of congenital progressive muscular dystrophy". Paediat. Univ. Tokyo 4: 5–8.
- "Fukuyama congenital muscular dystrophy". Genetics Home Reference. Retrieved 2012-11-26.
- Toda T, Yoshioka M, Nakahori Y, Kanazawa I, Nakamura Y, Nakagome Y (1995). "Genetic identity of Fukuyama-type congenital muscular dystrophy and Walker-Warburg syndrome". Ann. Neurol. 37 (1): 99–101. doi:10.1002/ana.410370118. PMID 7818265.
- Toda, Tatsushi; Kobayashi, Kondo-Lida, Sasaki, Nakamura (1 March 2000). "The Fukuyama congenital muscular dystrophy story". Neuromuscular Disorders 10 (3): 153–159. doi:10.1016/S0960-8966(99)00109-1. PMID 10734260. Retrieved 28 November 2012.
- Rutherford, Mary (2012). MRI of the Neonatal Brain. ISBN 0 7020 2534 8.
- Online 'Mendelian Inheritance in Man' (OMIM) 607440
- Saito, Kayoko. "Fukuyama Congenital Muscular Dystropy". Gene Reviews. National Center for Biotechnology Information. Retrieved 30 November 2012.
- Lopate, Glenn. "Congenital Muscular Dystrophy Treatment & Management". Medscape. Retrieved 30 November 2012.
- Fukuyama type muscular dystrophy at NIH's Office of Rare Diseases
- GeneReviews/NIH/UW entry on Fukuyama Congenital Muscular Dystrophy