Achondroplasia

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Achondroplasia
Definition of the disease
Achondroplasia a genetic disorder leading to the
malformation of ones bones due to an abnormality
in the conversion of cartilage to bone, causing
abnormally short stature. Also called
chondrodystrophia fetalis
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Causes risk factors

• Mutations (chemical changes) within a single gene
  cause achondroplasia. It is the mutation of the
  fibroblast growth factor receptor-3 (FGFR-3) gene
  found on human chromosome 4. The condition maybe
  passed from one generation to the next or it may
  result from a new mutation in a gene from
  average-sized parents.

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• Persons with achondroplasia have a 50 chance to
  pass the gene to the child, resulting in the
  condition, a 25 chance the child will inherit 1
  abnormal gene from each parent, which can lead to
  severe skeletal problems that often result in
  early death, and a 25 chance that the child will
  not inherit the gene and be of average height.

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Prevalence / Incidence

• Achondroplasia is the most common type of
  dwarfism. It occurs in all races and with equal
  frequency in males and females. Frequency is
  believed to be 1 in 25,000 births worldwide. It
  is estimated that there are 10,000 individuals
  with the condition in the United States.

Pathology
The basic defect is in the zone of chondroblast
proliferation in the physeal growth plates. As a
consequence, the bones pre-formed in
cartilage are markedly shortened in length. The
specific mechanisms by which the gene mutations
disrupt skeletal development remain elusive.
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Symptoms

• The typical appearance of achondroplastic
  dwarfism can be seen at birth. Symptoms may
  include
• Large head with prominent forehead (frontal
  bossing) and flat or even depressed area at the
  base of the nose
• Short stature
• Abnormal hand appearance (trident hand)
• Spinal stenosis
• Bowed legs or knock knee
• Frequent ear infections and sleep apnea
• Lordosis and/or kyphosis
• Hydrocephalus (water on the brain)
• Decreased muscle tone and loose joints
• Short fingers and toes
• Shortening of the proximal limbs (termed
  rizomelic shortening)
• Crowded or misaligned teeth

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Diagnosis

• Family Medical history is important in diagnosing
  before birth. A fetal ultrasound may show
  excessive amniotic fluid surrounding the fetus,
  with DNA testing to confirm ultrasound findings
  for parents who are at an increased risk for
  having a child with achondroplasia.
• Other indicators of achondroplasia include slow
  motor movement and low muscle tone. Walking
  doesnt occur until between 24 and 36 months.

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Treatment

• Currently there is no cure for achondroplasia.
  Growth-hormone treatment seems to increase the
  rate of growth during the first year of
  treatment, but doesnt substantially affect or
  increase height. Surgery to lengthen arms and
  legs of people with the condition may be
  considered in some very specialized cases and
  done on experimental basis in a few centers in
  the U.S., but it is not a common practice because
  complications are frequent and the process is
  long, arduous, and very painful.
• Related abnormalities should be treated when they
  cause problems.

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Prevention

• Genetic counseling may be helpful for prospective
  parents when 1 or both have achondroplasia.
  However, because achondroplasia most often
  develops spontaneously to average-sized parents,
  prevention is not always possible.