What is Fukuyama congenital muscular dystrophy (FCMD)?
FCMD is a rare congenital muscular dystrophy that is found almost exclusively in Japan. The condition predominantly affects the muscles, brain, and eyes. Congenital muscular dystrophies are a group of genetic conditions that cause muscle weakness and wasting (atrophy) beginning very early in life.
What are the symptoms of FCMD?
Fukuyama congenital muscular dystrophy affects the skeletal muscles, which are muscles the body uses for movement. The first signs of the disorder appear in early infancy and include a weak cry, poor feeding, and weak muscle tone (hypotonia). Weakness of the facial muscles often leads to a distinctive facial appearance including droopy eyelids (ptosis) and an open mouth. In childhood, muscle weakness and joint deformities (contractures) restrict movement and interfere with the development of motor skills such as sitting, standing, and walking.
Fukuyama congenital muscular dystrophy also impairs brain development. People with this condition have a brain abnormality called cobblestone lissencephaly, in which the surface of the brain develops a bumpy, irregular appearance (like that of cobblestones). These changes in the structure of the brain lead to significantly delayed development of speech and motor skills and moderate to severe mental retardation. Social skills are less severely impaired. Most children with Fukuyama congenital muscular dystrophy are never able to stand or walk, although some can sit without support and slide across the floor in a seated position. More than half of all affected children also experience seizures.
Other signs and symptoms of Fukuyama congenital muscular dystrophy include impaired vision, other eye abnormalities, and slowly progressive heart problems after age 10. As the disease progresses, affected people may develop swallowing difficulties that can lead to a bacterial lung infection called aspiration pneumonia. Because of the serious medical problems associated with Fukuyama congenital muscular dystrophy, most people with the disorder live only into late childhood or adolescence.
Who is at risk of getting FCMD?
Fukuyama congenital muscular dystrophy is extremely uncommon in the western country. However, it is the second most common form of childhood muscular dystrophy and one of the most common autosomal recessive disorders in Japan; the incidence is about one-half to one third that of Duchene muscular distrophy
Is there any other names for this condition?
Yes, these include:
- Cerebromuscular Dystrophy, Fukuyama Type
- Micropolygyria With Muscular Dystrophy
- Muscular Dystrophy, Congenital Progressive with Mental Retardation
- Muscular Dystrophy, Congenital With Central Nervous System Involvement
- Congenital Muscular Dystrophy, Fukuyama Type
- Muscular Dystrophy, Congenital, Fukuyama Type
- Muscular Dystrophy, Fukuyama Type
How do people inherit Fukuyama congenital muscular dystrophy?
This condition is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell have mutations. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition. The chromosome that carriers the gene mutation is chromosome 9 and this mutation causes the protein, Fukutin to not function properly.
A complete set of human chromosomes contains twenty three (23) pairs. The exact position of a gene within these chromosomes is called its locus. A locus is similar to a “map coordinate” for a gene on a chromosome. Geneticists identify genes with short and unique names, much the same way that a chemical element has a short symbol name, or that a particular stock has a ticker-symbol. A gene’s name is often (but not always) related to the product it produces when the cell’s biological machinery decodes it. This protein or enzyme is usually related to the disorder somehow. Potential treatments for any genetic disorder would probably involve repairing or removing the gene product.
How is it diagnosed?
The diagnosis starts with a physical exam. Usually before 9 months of age, the baby appears ‘floppy’ (hypotonia) meaning they are unable to support their limbs. Often there is a delay in development and weakness in the muscles. There is also a facial features that indicate FCMD including enlargement (hypertrophy) of the cheeks a tendency for the mouth to remain half open from infancy. Seizure may occurs in about half of the cases.
Blood tests are often performed to test for an enzyme known as creatine kinase (or CK). This enzyme becomes present in the blood when muscle cells break down and is found in everyone. However, elevated levels of CK mean that the cells in the muscles are breaking down faster than they should be and can be detected by blood test.
Brain imaging such as MRI and CT scans may also be used to look for signs of FCMD. Muscle and nerve reaction testing are also likely to be performed.
Because the symptoms of FCMD can also occur in other condition, other tests may also be performed in order to rule out any other condition.
What is the prognosis?
The clinical course is usually progressive and few patients are able to walk. Unfortunately, death usually results from respiratory complications during the 1st decade of life although some patients may survive into adolescence.