Infants with Fukuyama congenital muscular dystrophy are “floppy” at birth and usually have problems sucking and swallowing. They have a weak cry and there is a loss of muscle tone as well as weakness of the muscles. The joints in the knees and elbows may be in a fixed position (contractures) and reflexes of the tendons are poor.
Mental retardation is characteristic of this form of muscular dystrophy. Also, some affected infants and children have seizures. A sunken chest, and a severe form of grand mal seizures called status epilepticus has been found in a few individuals with FCMD.
Fukuyama congenital muscular dystrophy is inherited as an autosomal recessive trait. It occurs as a result of a gene mutation on the long arm of chromosome 9 (9q31). This gene gives instructions for the production of (codes for) a protein known as fukutin. The normal role of this protein isn’t yet well understood.
Chromosomes, which are present in the nucleus of human cells, carry the genetic information for each individual. Human body cells normally have 46 chromosomes. Pairs of human chromosomes are numbered from 1 through 22 and the sex chromosomes are designated X and Y. Males have one X and one Y chromosome and females have two X chromosomes. Each chromosome has a short arm designated “p” and a long arm designated “q”. Chromosomes are further sub-divided into many bands that are numbered. For example, “chromosome 9q31″ refers to band 31 on the long arm (q) arm of chromosome 9. The numbered bands specify the location of the thousands of genes that are present on each chromosome.
Genetic diseases are determined by the combination of genes for a particular trait that are on the chromosomes received from the father and the mother.
Recessive genetic disorders occur when an individual inherits the same abnormal gene for the same trait from each parent. If an individual receives one normal gene and one gene for the disease, the person will be a carrier for the disease, but usually will not show symptoms. The risk for two carrier parents to both pass the defective gene and, therefore, have an affected child is 25% with each pregnancy. The risk to have a child who is a carrier like the parents is 50% with each pregnancy. The chance for a child to receive normal genes from both parents and be genetically normal for that particular trait is 25%. The risk is the same for males and females.
All individuals carry 4-5 abnormal genes. Parents who are close relatives (consanguineous) have a higher chance than unrelated parents to both carry the same abnormal gene, which increases the risk to have children with a recessive genetic disorder.
Dominant genetic disorders occur when only a single copy of an abnormal gene is necessary for the appearance of the disease. The abnormal gene can be inherited from either parent, or can be the result of a new mutation (gene change) in the affected individual. The risk of passing the abnormal gene from affected parent to offspring is 50% for each pregnancy regardless of the sex of the resulting child.
Fukuyama type congenital muscular dystrophy is almost nonexistent in the United States, but in Japan is second only to Duchenne muscular dystrophy in frequency. The incidence in Japan is reported as about 0.7-1.2 cases per 100,000 children.
The diagnosis depends on a thorough physical examination and medical history. In addition, the physician will look for information to assist in the diagnosis from several tests such as blood tests to detect abnormally high levels of a particular enzyme (creatine kinase) released form the cells of damaged muscles, and blood fukutin gene mutations, electromyographic studies to determine the area of muscle that is damaged, and muscle biopsy to distinguish muscular dystrophy from other neuromuscular disorders.
Patients with Fukuyama congenital muscular dystrophy may benefit from physical therapy to help prevent joints from becoming fixed.
For patients who have seizures, anti-convulsant drugs such as phenytoin, valproic acid, phenobarbitol, clonazepam, ethusuximide, primidone, corticotropin, and corticosteroid drugs may help prevent and control seizures.
Genetic counseling will be of benefit for patients and their families.
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Contact for additional information about Fukuyama type congenital muscular dystrophy:
Chang-Yong Tsao, MD, FAAN, FAAP
Professor of Clinical Pediatrics and Neurology
Nationwide Children’s Hospital
College of Medicine
Ohio State University
Columbus, Ohio 43210
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