What Causes Spinal Muscular Atrophy?
Spinal Muscular Atrophy is an autosomal recessive
disease, which means that both parents must be carriers. Both
parents must have the gene responsible and these genes must be
passed onto their child. When a child has received this gene
from each of its parents it will than be affected by SMA.
Although both parents are carriers the likelihood of passing
this gene along to a child and having an affected child is 25%,
or 1 in 4.
Familial Forms (affecting other family members) of Spinal
Muscular Atrophy in the older age group can occur as autosomal
recessive, mutants or autosomal dominant. The genetic defects
underlying these diseases make it necessary to be precise
regarding the inheritance pattern in a particular family.
Quick Facts about Spinal Muscular
Spinal muscular atrophy (SMA), the number one genetic killer
of children under the age of two, is a group of inherited and
often fatal diseases that destroys the nerves controlling
voluntary muscle movement, which affects crawling, walking, head
and neck control, and even swallowing.
WHO IS AFFECTED?
SMA is one of the most prevalent genetic disorders.
One in every 6,000 babies is born with SMA. Of children
diagnosed before age two, 50 percent will die before their
second birthday. SMA can strike anyone of any age, race or
gender. One in every 40 people carries the gene that causes SMA.
The child of two carriers has a one in four chance of developing
THE TYPES OF SMA
Type 1, or Werdnig-Hoffmann Disease, is the most
severe form of SMA. Children with Type I tend to be weak and
lack motor development, rendering movement difficult. Children
afflicted with Type I cannot sit unaided and have trouble
breathing, sucking and swallowing. Type I SMA strikes infants
between birth and six months.
Type II is slightly less severe. Type II patients may
be able to sit unaided or even stand with support and usually do
not suffer from feeding and swallowing difficulties. However,
they are at increased risk for complications from respiratory
infections. Type II SMA affects infants between seven and 18
Type III, also known as Kugelberg-Welander Disease, is
the least deadly form of childhood-onset SMA. Type III patients
are able to stand, but weakness is prevalent and tends to
eventually sentence its victims to a wheelchair. Type III SMA
strikes children after the age of 18 months, but can surface
even in adulthood.
Type IV is the adult form of the disease in which
symptoms tend to begin after age 35. Symptoms usually begin in
the hands, feet and tongue, and spread to other areas of the
Adult Onset X-Linked SMA, also known as Kennedy's
Syndrome or Bulbo-Spinal Muscular Atrophy, occurs only in men.
Facial and tongue muscles are noticeably affected. In addition,
these men also often have breast enlargement known as
gynecomastia. Like all forms of SMA, the course of the disease
is variable, but in general tends to progress slowly.
SMA does not affect sensation and intellectual activity in
patients. It commonly is observed that patients with SMA are
unusually bright and sociable.
What Is Spinal Muscular Atrophy?
Spinal Muscular Atrophy (SMA) is a disease of the anterior
horn cells. Anterior horn cells are located in the spinal cord.
SMA affects the voluntary muscles for activities such as
crawling, walking, head and neck control and swallowing.
It mainly affects the proximal muscles, or in other words the
muscles closest to the point of origin, in this case those
closest to the trunk of one's body. Weakness in the legs is
generally greater than weakness in the arms. Some abnormal
movements of the tongue, called tongue fasciculations may be
present in patients with Type I and some patients with Type II.
The senses/feelings are normal as is intellectual activity. In
fact it is often observed that patients with SMA are unusually
bright and sociable.