Principal Causes of Dwarfism

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Principal Causes of Dwarfism*


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, 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

• Achondroplasia
• Pseudoachondroplasia
• Spondyloepiphyseal Dysplasia
• Kniest Dysplasia
• Diastrophic  Dysplasia (Diastrophic

• Osteogenesis Imperfecta

Metabolic Bone Dwarfism

• Morquio Syndrome
• Hypopituitarism

Secondary Bone Dwarfism

• Seckel Syndrome
• Turner Syndrome
• Intrauterine Growth Retardation


Constitutional Bone Dwarfism

These types of dwarfism cause growth and developmental abnormalities in bones and cartilage. They also affect skeletal structure and morphology.

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.

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.

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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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These informations were taken and adapted from Nathalie Boëls' book: Le nanisme: Se faire une place au soleil dans un monde de grands, Ed., CHU Ste-Justine, 2008 and from Recherche médicale sur le nanisme (Association québécoise des personnes de petite taille, 1993)



© 2011 AQPPT - Translated by George Bravo and Judy Murphy