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There are
many causes of dwarfism. It would be impossible to look at all of them
and only the most common ones will be discussed here. For more
information, you can refer to the ORPHANET database at HYPERLINK www.orpha.net,
a site dedicated to rare diseases, including those related to dwarfism.
Among the
500 or so known diseases related to dwarfism, there are three main
groups depending on which physiological mechanism is involved.
Constitutional
Bone Dwarfism
These types of dwarfism cause growth and developmental abnormalities in
bones and cartilage. They also affect skeletal structure and
morphology.
Achondroplasia
Disproportionate Dwarfism
Achondroplasia is the most common and most well-known cause of
dwarfism. In the past, people tended to talk so much about
achondroplasia in front of little people that even today they wrongly
think they have it.
As the
epiphysial cartilage doesn’t form properly, long bone development (arm
and leg bones) will be slower, more difficult, and end at a slightly
earlier age. The average height of an adult male with achondroplasia is
125 cm. An average female’s height is 120 cm. .
This type of
dwarfism is generally detected at birth by characteristic facial
features: a round and disproportionate head in comparison to the rest
of the body, a prominent forehead, and a low nasal bridge.
Pseudoachondroplasia
Disproportionate Dwarfism
As indicated by the name of the disease, people suffering from
pseudoachondroplasia look very similar to people with achondroplasia.
For this reason, these two types of dwarfism have been confused with
one another for a long time. People with pseudoachondroplasia have
short limbs and a head and trunk of normal size; the face is
unaffected. This disease is also characterized by a waddling gait and
double-jointedness. The average adult height is 110 cm.
Spondyloepiphyseal
Dysplasia
Proportionate Dwarfism
The trunk and the limbs are shorter but in proportion. The face and
skull are unaffected and the hands and feet are normal size. However,
the neck is shorter, giving the person a stocky appearance. The sternum
is prominent and adults reach on average 135 cm. This prognostic
depends, however, on how badly the disease has affected the hips – this
can be quite severe.
Kniest
Syndrome (or Dysplasia)
Proportionate Dwarfism
Adults have an average height of 135 cm; the height of children is well
below average. In proportionate dwarfism the trunk and limbs are in
proportion to each other. The face has characteristic features: it is
very round and the nasal bridge (between the eyes) is flattened. The
nose is very small, the legs are often bowed inwards or outwards, and
the fingers are long and slender, making them look delicate.
Diastrophic Dysplasia (or Diastrophic
Dwarfism)
Disproportionate Dwarfism
Diastrophic dwarfism is characterized by very deformed limbs. A person
with diastrophic dysplasia will have clubfoot and, because the illness
affects the long bones, their limbs will be much shorter in comparison
with the rest of their body. The face and skull are unaffected but the
ears are low. The hands and feet are thick, the ring finger is longer
than normal, and the pointer finger is shorter. The back is often
affected by scoliosis and kyphosis. Joint mobility, particularly in the
hips, knees, shoulders and ankles, is limited, making walking difficult
and exhausting. Children are very small, and the average adult height
is 120 cm.
Osteogenesis Imperfecta
Proportionate or Disproportionate
Dwarfism, depending on the type
There are four different types of osteogenesis imperfecta and not all
of them lead to dwarfism.
This
illness, commonly called "glass bone disease", causes increased bone
malleability and brittle bones. Brittle bones cause fractures and bone
deformations. Fractures occur either at random or after minor trauma.
Deformations from fractures or bone malleability can be extremely
severe and lead to seriously deformed dwarfism. The sclera (the white
part of the eyes) can be blue and young people sometimes go deaf after
adolescence.
Metabolic
Bone Dwarfism
Metabolism is the set of chemical reactions that turn an ingested
substance into something the body can use such as a basic nutrient or a
source of energy. In the case of some diseases, flaws may occur during
metabolism. When the metabolism of calcium, phosphorous, carbohydrates,
and fats is flawed, bone growth and structure may be affected.
Morquio Syndrome
Disproportionate Dwarfism
Morquio syndrome is the second most frequent type of dwarfism in
Québec. It is a severe form of dwarfism. People stop growing at 8 to 10
years old, reaching on average a height of 1 m, rarely exceeding 125
cm. They often have difficulty walking (waddling gait) or have a
deformed thoracic cavity and sternum; the thoracic cavity sticks out
dramatically in the front of the torso. The arms and legs are normal
size but often deformed; the trunk is short and wide. The neck is
shorter than normal, giving the person a stocky appearance. Joints,
especially the hip joints, are weak.
Hypopituitarism (Pituitary Dwarfism)
Proportionate Dwarfism
Located at the base of the brain, the pituitary gland is a small gland
that produces several essential hormones, including growth hormones.
People suffering from pituitary dwarfism produce fewer pituitary
hormones (including growth hormones), causing their growth rate to slow
down. However, this type of dwarfism is easily and efficiently treated
with growth hormone injections (see the section Treatment and Prevention).
Therefore, it is essential to diagnose pituitary dwarfism as early as
possible.
Secondary
Bone Dwarfism
Bone disorders play a role in the diagnosis of these types of dwarfism,
but their symptoms are secondary.
Seckel Syndrome
Proportionate Dwarfism
This form of dwarfism is quite rare and is characterized by the shape
of the face, which is very small. The forehead is low and receding, and
the lower jawbone is set back from the upper jawbone. The nose is
curved and shaped like a bird beak, which is why this form of dwarfism
is sometimes called “bird-head dwarfism.” The trunk and limbs are
short, making it proportionate dwarfism. The height of adults varies
but is often less than 128 cm.
Turner Syndrome
Proportionate Dwarfism
Only females suffer from this type of dwarfism. It results from having
only one X chromosome instead of two. Their average height reaches 140
cm if they do not receive growth hormone treatment. They are infertile.
Intrauterine Growth Retardation (or
Primordial Dwarfism)
Proportionate Dwarfism
Although they are born at term, some children are smaller at birth.
Many will never make up this loss in height but will become
well-proportioned, small adults. The causes of intrauterine growth
retardation are many and diverse, but they are not fully understood.
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