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Skeletal Dysplasias

Overview

Skeletal dysplasias are a complex group of bone and cartilage disorders that may affect the fetal skeleton as it develops in utero.

As a whole, skeletal dysplasias are not common. They affect one in every 4,000-5,000 births, although the incidence may be higher since the symptoms may not manifest until early childhood, when short stature, joint abnormalities or other complications arise.

Symptoms of skeletal dysplasias

SLIDESHOW APPEARS HERE

To date, more than 350 distinct skeletal disorders have been described which may result in numerous anomalies in the shape and size of the skeleton.

Some symptoms of skeletal dysplasias include:

Causes of skeletal dysplasias

The causes of skeletal dysplasias are nearly as diverse as the number of distinct disorders. Generally, however, the causes can be cataloged into three groups:

Nearly half of the documented skeletal dysplasias are caused by a genetic mutation that makes prenatal diagnosis possible through genetic testing. For details, see common skeletal dysplasias and symptoms.  

Evaluation and diagnosis

The fetal skeleton is usually evaluated as part of a routine ultrasound, usually around week 20 of the pregnancy.

If a skeletal dysplasia is suspected, the mother will likely be referred to a facility that specializes in diagnosing, treating and caring for babies with congenital anomalies, such as the Center for Fetal Diagnosis and Treatment at The Children’s Hospital of Philadelphia.

At our Center, prenatal evaluation of skeletal dysplasias includes a detailed ultrasound of the fetal skeleton in the second or third trimester of gestation, and an extensive genetic family history work up.

But prenatal diagnosis of skeletal dysplasias remains challenging, especially when there is no family history of the disorders. This is because:

In the evaluation of skeletal dysplasias, CHOP has expanded its fetal imaging abilities beyond ultrasound and MRI to also include low-dose fetal computed tomography (CT).

Low-dose fetal CT

The low-dose fetal CT program at CHOP was initiated in 2008 as a new powerful imaging tool to aid in diagnosing skeletal dysplasias and improving our ability to counsel patients with these fetal anomalies.

The CT scan includes only the part of the uterus where the fetus is. Once the scan is done, the images then undergo post-imaging computer-aided renderings to create multiple two- and three-dimensional pictures of the fetal skeletal system that depict the bones in exquisite detail.

Initial interpretation of the fetal CT is performed by pediatric radiologists who work closely with the Center for Fetal Diagnosis and Treatment and who have vast experience and expertise in prenatal diagnosis. The final diagnosis for each specific patient requires a multidisciplinary team including radiologists, obstetricians and geneticists.

Much care and thought is required before deciding who is a candidate for low-dose fetal CT because of the obvious risk of radiation to the growing fetus.

When the ultrasound exam demonstrates severe bone abnormalities and the diagnosis is indeterminate, the decision to undergo the study is reached by a multidisciplinary team involving obstetricians, geneticists, radiologists and sonographers.

Radiation dose is kept to a strict minimum, adhering to the principles of ALARA, or As Low As Reasonably Achievable. Also, these CTs are only done in the second and third trimesters of gestation, when fetal organs have already formed and developed, and never during the first trimester, when the fetus is most sensitive to radiation.

By providing detailed visualization of the fetal bones, low-dose fetal CT allows us to provide improved parental counseling, predelivery planning and postnatal management in fetuses with a diagnosis of skeletal dysplasia.

Long-term outlook

The long-term outlook for patients with skeletal dysplasias varies greatly depending on the type of dysplasia, as well as associated abnormalities. About half of affected fetuses with skeletal dysplasia are stillborn or die within the first six weeks of life.

But not all children with dysplasias have severe medical problems. Many of these children can live relatively normal lives.

It is recommended that children born with or later diagnosed with a skeletal dysplasia be treated by a multidisciplinary team of experts, such as the one at The Children’s Hospital of Philadelphia.

By working with a coordinated team of geneticists, neonatologists, radiologists, orthopaedists, pediatricians and specialists, your child will receive individualized care that addresses your child’s health, developmental and psychosocial issues.

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Common skeletal dysplasias and symptoms

Thanatophoric dysplasia

Camptomelic dysplasia

Achondroplasia

Osteogenesis imperfecta

Achondrogenesis

May 2012

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How a baby’s skeleton develops

Development of a fetal skeleton typically follows a programmed pattern of bone development. Typical fetal development includes:

  • 5 weeks: Neural tube forms. This will develop into the baby’s brain, spinal cord, back bone and nerves.
  • 8 weeks: Collar bones and lower jaw form
  • 12 weeks: Arms and legs, shoulder blades and final portion of the small intestine form
  • 12-16 weeks: Bones in the hands and feet form
  • About 20 weeks: Centers of ossification in the different bones form

When the pattern is disrupted – by inherited gene, toxic substance or unknown reason – it can lead to skeletal dysplasias.