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Amniotic Band Syndrome


Types and clinical signs

An amniotic band is a membrane formed in the amniotic cavity surrounding the fetus. This membrane may envelop and constrict the fetus to the point where organs or limbs entrapped in it can be amputated. The outcome and severity depend on the stage of pregnancy when the membrane was formed and which organs or limbs were entrapped. This syndrome is also referred to as the ADAM (Amniotic Deformities, Adhesion, Mutilation) complex.

A membrane formed at an early stage of pregnancy may cause severe damage to the structure of the various tissues, resulting in deformities in a large number of organs - this often results in intrauterine death. Defects in these cases usually include defects in the location and structure of the heart, omphalocele, gastroschisis, anencephalus, cleft face, hydrocephalus, etc.

A membrane formed at a later stage of pregnancy may not cause damage, but if it does, this is usually to limbs. The entire limb, or part of it, or only digits can be involved, and the result can be limb stumps or scars in one or more limbs. Often those fingers that are not missing in the limb involved have signs of scarring or fusion.

Sometimes the damage is milder, manifesting as a localized annular narrowing at the site where the membrane entrapped the limb, with swelling distal to the ring due to lymphedema.



Inheritance pattern

The cause of the membrane in the amniotic sac is not genetic or hereditary in the vast majority of cases, but may be in some.

It may be a result of abdominal trauma or hemorrhaging into the amniotic sac, although there have been isolated cases of hereditary transmission.

There are a number of mostly autosomal recessive syndromes that feature missing limbs, and it is important to distinguish these from an amniotic band. Hereditary disorders should be suspected particularly if the defect is symmetrical in a number of limbs and an amniotic band is not found. It is common to find local skin agenesis on the posterior part of the scalp - this manifests as a round area of about 1 cm diameter without hair.

Penetrance

Not known in the genetic types.

Associated features that can be demonstrated in tests performed during pregnancy

Ultrasound examination may reveal abnormalities including dilated cerebral ventricles if the face is affected. Other common findings include short umbilical cord, lordosis and intrauterine growth retardation.

In all these cases it is important to refer the couple for genetic counseling, to which they should bring all data, including the results of other tests performed during the pregnancy such as alpha-fetoprotein, nuchal translucency, etc. The ultrasound system scan should be directed at the 4 limbs, lips, structure of the face, cerebral ventricles, which may be dilated if the face is affected, head, structure of the genitals, etc.

In cases of a significant amniotic band it is advisable to refer the parents to a multidisciplinary clinic in a hospital for professional counseling by a geneticist, an expert in ultrasound examinations, a pediatric orthopedist or surgeon, and a neonatologist, in order to collate all the data and discuss the various risks in each specific case, the method of monitoring the fetus, possible intervention if indicated, etc. The decisions taken will depend on the severity of the problem, the presence of additional findings, etc.

What is the risk of recurrence in a subsequent pregnancy?

Amniotic band syndrome does not tend to recur, and the additional risk in subsequent pregnancies, if present, is minimal. The risk for more distant relatives can be established within genetic counseling based on the cause of the limb defect, the pedigree, the results of tests such as chromosome analysis, etc.

Molecular genetic information

The gene for the disease

No gene is known.

Location

Not known.

Genetic testing

Diagnostic testing

Not available

Carrier testing

Not available

Fetal testing

Ultrasound examination only
 
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