Werdnig-Hoffman Disease is passed to children from their parents in what is called an autosomal recessive pattern of inheritance. This means that each parent carries a gene for the disorder without knowing it; if one of their children inherits both of these genes, that child will develop the disorder. Both parents must be carriers of the abnormal gene and both must pass this gene on to their child. Although both parents are carriers the likelihood of a child inheriting the disorder is 25%, or 1 in 4.
An individual with SMA has a missing or mutated gene (SMN1, or survival motor neuron 1) that produces a protein in the body called Survival Motor Neuron (SMN) protein. This protein deficiency has its most severe affect on motor neurons. Motor neurons are nerve cells in the spinal cord which send out nerve fibers to muscles throughout the body. Since SMN protein is critical to the survival and health of motor neurons, without this protein nerve cells may atrophy, shrink and eventually die, resulting in muscle weakness. Everybody is born with too many nerve cells; the extra, unnecessary cells are programmed by the body to die off. Healthy children have a gene (SMN1, or survival motor neuron 1)that is able to tell the body when enough nerve cells have died. Children born with Werdnig-Hoffman Disease, however, don�t have this gene; nerve cells keep dying and soon the body and its muscles are affected.
Children with Werdnig-Hoffman Disease have normal intelligence
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Children with Werdnig-Hoffman Disease (SMA Type 1) are usually diagnosed before they turn 6 months old. They may do well for several months, but then they usually begin to have problems feeding or moving. They will no longer be able to hold their heads up, or they may no longer be able to turn their heads. The following symptoms are also likely to be present:
1. Weak muscles
2. Decreased muscle tone (hypotonia)
3. Decreased muscle size (atrophy)
4. Decreased reflexes
5. Decreased joint movements (contractures)
6. Irregular breathing patterns that show the chest
collapsing when an infant breathes in
7. Bell-shaped chest
8. Decreased movement of fingers and toes
9. Back and forth movements of the tongue (fasciculations)
Investigations.
Investigations performed on an infant suspected of having Werdnig-Hoffman disease may include: -
Serum creatine kinase levels- usually normal but may be raised.
Genetic studies
EMG - may be difficult to interpret in young infants, may see evidence of denervation and reinnervation with normal conduction velocities.
Muscle biopsy
Congenital contractures seen in Werdnig-Hoffman disease may be difficult to differentiate from those seen in the more benign condition arthrogryposis multiplex congenita
Treatment
Treatment for Werdnig-Hoffman Disease focuses on both symptomatic relief and supportive care. Children may benefit from physical therapy and mechanical devices that help them eat. Children whose muscles are too weak to allow them to breathe will require help from a ventilator machine.
The parents of any child born with Werdnig-Hoffman disease will need support throughout the lifetime of the child and beyond. They may find it helpful to talk to other affected families. Parents may wish to have genetic counselling before considering any further pregnancies. Pre-natal testing is available for families who have had an affected child. The child may benefit from physiotherapy and respiratory support for the relief of symptoms. It must be remembered that it is only motor function that is affected in these children and that their sensation and intellect is normal, parents should therefore be encouraged to cuddle and interact with the child as normal, for the well being of both parties.
Prognosis
The outlook for children with Werdnig-Hoffman disease is very poor. The greatest risk they face is catching a cold or infection. Fifty percent of Type I babies will die before their 2nd birthday.
At this time, there is no cure for Werdnig-Hoffman Disease, although researchers remain hopeful.
