Types of Spinal Muscular Atrophy
Spinal Muscular Atrophy: Types list
The list of types of Spinal Muscular Atrophy mentioned in various sources includes:
Genes and Disease by the National Center for Biotechnology (Excerpt)
The age of onset and severity of SMA varies from an infantile onset form (type I) which causes early death from respiratory failure, to milder juvenile onset forms in which affected individuals show reduced life expectancy (type II), and are unable to walk (types II and III).
(Source: Genes and Disease by the National Center for Biotechnology)
NINDS Spinal Muscular Atrophy Information Page: NINDS (Excerpt)
There are many
types of SMA; some of the more common types are described below.
SMA type I, also called Werdnig-Hoffmann disease, is
evident in utero or within the first few months of life. There may be a
paucity of fetal movement in the final months of pregnancy. Symptoms may
include hypotonia (floppiness of the limbs and trunk), diminished limb
movements, swallowing and feeding difficulties, and impaired breathing.
Affected children never sit or stand and usually die before the age of 2.
Symptoms of SMA type II usually begin between 3 and 15 months of
age. Features may include inability to stand or walk, respiratory
problems, hypotonia, decreased or absent deep tendon reflexes, and muscle
fasciculations (involuntary contractions of small bundle muscle, evident
as twitching of limb or tongue muscles). These children may learn to sit
but do not stand. Life expectancy varies.
Symptoms of SMA type III (Kugelberg-Welander disease) appear
between 2 and 17 years of age, and include abnormal gait; difficulty
running, climbing steps, or rising from a chair; and a fine tremor of the
The childhood SMAs are all autosomal recessive diseases. This means
that they are familial and more than one case is likely to occur in the
same generation of a family - in siblings or cousins. The parents are
usually asymptomatic but carry the gene. Cousin marriages are more common
in these families than in others. If one case has occurred in a family,
antenatal diagnosis can be made in a subsequent pregnancy. The gene and
gene product have been identified providing accurate diagnostic tests.
Kennedy syndrome or progressive spinobulbar muscular
atrophy may occur between 15 and 60 years of age. Features of this
type may include weakness of the facial and tongue muscles, dysphagia
(difficulty swallowing), dysarthria (speech impairment), and gynecomastia
(excessive development of male mammary glands). The course of the disorder
varies but is generally slowly progressive. Kennedy syndrome is an
X-linked recessive disorder, which means that it occurs only in men. Women
carry the gene. A diagnostic DNA test is available.
Congenital SMA with arthrogryposis (persistent contracture of
joints with fixed abnormal posture of the limb) is a rare disorder.
Manifestations include severe contractures, scoliosis (curvature of the
spine), chest deformity, respiratory problems, micrognathia (unusually
small jaws), and ptosis (drooping of upper eyelids). Adult SMA may
begin between 40 and 60 years of age and progresses rapidly, with an
average life expectancy of about 5 years. Most cases prove to be variants
of amyotrophic lateral sclerosis. Symptoms include progressive limb
weakness and atrophy of the muscles, difficulty speaking and swallowing,
and respiratory problems.
(Source: excerpt from NINDS Spinal Muscular Atrophy Information Page: NINDS)
Spinal Muscular Atrophy: Related Disease Topics
More general medical disease topics related to Spinal Muscular Atrophy include:
Research More About Spinal Muscular Atrophy