Caudal Dysplasia Health Article

Definition

Caudal dysplasia is a total or partial failure of development of the lower vertebrae, including the sacrum (tailbone), which results in associated abnormalities of the lower extremities (legs), spine, kidneys, gastrointestinal and genitourinary tracts.

Description

Caudal dysplasia is also known as sacral agenesis, sacral regression, caudal aplasia, caudal regression sequence, or sirenomelia. Caudal dysplasia results from a failure of the caudal or lower region of the spinal column to form correctly. This abnormal development of the lower spine causes a wide range, or spectrum, of other abnormalities. On the mild end of the spectrum, there may be a partial absence of the tailbone with no associated symptoms (sometimes picked up accidentally on x ray), and on the severe end of the spectrum, there can be complete absence of the kidneys, openings on the spinal cord, genitourinary, limb and bowel abnormalities. Some of these more serious abnormalities can be life-threatening. Most infants with caudal dysplasia fall in between the two ends of the spectrum. They may have kidney malformations, gastrointestinal malformations, spinal cord problems, heart abnormalities, and problems with their lower limbs.

Sirenomelia is a rare condition that was once thought to represent the most severe end of the caudal dysplasia sequence. Infants with sirenomelia may have complete fusion of the lower limbs, complete or partial renal agenesis, and severe bowel problems. There is often oligohydramnios, or a low amount of amniotic fluid, during pregnancy. Because of the severity of the defects in this condition, it is generally lethal. As of 2005, sirenomelia is now thought to be a separate syndrome.

Caudal dysplasia is caused by a problem with the formation of certain tissues early in pregnancy. The lower spine is usually completely formed by the seventh week of pregnancy. Caudal dysplasia is a primary defect of formation of the tissues that will become the sacrum, spinal cord, kidneys, and gastrointestinal system.

Genetic profile

The genetics of caudal dysplasia are not well understood. There is no convincing evidence that this is a genetic disorder. Some families have shown autosomal dominant inheritance, but more research will be necessary before the exact pattern of inheritance of this disorder is clear. In most cases, it occurs as an isolated event. In some families, there is evidence of an increased incidence of mild scoliosis and spina bifida occulta (opening on one or more of the vertebra without any physical effect) in the parents of children affected with caudal agenesis. This suggests that there may be some genetic factors that predispose some individuals to have caudal dysplasia but, as of 2005, these factors are not well understood.

Demographics

Estimates of the incidence of caudal dysplasia range between approximately one in 7,500 to one in 20,000 births. Caudal dysplasia occurs equally in males and females. There is an increased rate of caudal dysplasia among infants of diabetic mothers. As many as 16–22% of infants with caudal dysplasia are born to diabetic mothers, and the risk for a diabetic woman (with poor glucose control) to have an infant with caudal dysplasia is 200 times higher that the average population risk. Diabetes or impaired glucose metabolism is a common problem in pregnancy with 3–10% of all pregnancies affected by abnormal glucose metabolism. The exact mechanism by which diabetes causes caudal dysplasia in not well understood.

Caudal dysplasia is a defect of the mesodermal tissue, which develops early in the first trimester of pregnancy. Poor glucose control during the first trimester can lead to an increased risk for the fetus to develop caudal dysplasia. The interaction between poor glucose control and the defects that lead to problems in the mesodermal tissues is not well understood.

Most women with an increased risk to have a child with caudal regression have diabetes (often undiagnosed) prior to pregnancy. Gestational diabetes (or diabetes that develops during pregnancy) is a separate entity and should not be confused with diabetes in the first trimester. Gestational diabetes is not associated with an increased risk for caudal dysplasia.