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Roberts SC phocomelia

Roberts SC phocomelia

Definition

Roberts SC phocomelia is a rare genetic condition that causes severe abnormalities in arm and leg bones. Other abnormalities, such as mental retardation, may also be present.

Description

Roberts SC phocomelia was first described in the year 1919. In the past, Roberts SC phocomelia syndrome was described as two separate syndromes: Roberts syndrome, and SC or pseudo-thalidomide syndrome. More recent examination, however, indicated that they are the same disorder. The term "pseudo-thalidomide" was originally used to describe individuals with limb shortening, as the medication thalidomide is known to cause limb abnormalities in the babies of women taking it during pregnancy.

Phocomelia is a condition in which the hands and feet are present, but the arms and legs are absent. The hands and feet are attached directly to the body. Usually there is greater shortening in the arms than in the legs. People with Roberts SC phocomelia syndrome have varying degrees of hypomelia, which means that the limbs are not fully developed. Some are born without the upper bones of the arms or the legs. This is referred to as tetraphocomelia. Some people, though, have a less severe form of limb shortening.

In addition to the limb abnormalities, 80% of individuals with the syndrome have a small head (microcephaly). In addition, most people with the syndrome have some degree of mental retardation. Most also have facial problems affecting the development of the upper lip (cleft lip) and incomplete development of the palate (the roof of the mouth).

Genetic profile

Roberts SC phocomelia is inherited in an autosomal recessive fashion. This is a pattern in which the child receives one nonfunctioning (abnormal) gene from each parent. When a woman and man who both carry one abnormal gene for Roberts SC phocomelia have children, there is a 25% chance that they will each pass along the gene for the syndrome. People who are termed "carriers" are not affected by the disorder, as they have only one copy of the gene that causes Roberts SC phocomelia. The chances are 50% that they will have a child who is also a carrier of the disorder. The chances are 25% that they will have a baby who is neither a carrier nor affected with Roberts SC phocomelia.

The specific gene that causes the syndrome is not yet known, and there is no direct genetic test to identify a potential carrier of the disease.

In many of the individuals who have been diagnosed with Roberts SC phocomelia, a unique feature may be observed on some of their chromosomes . The exact association of this unusual observation with the syndrome is not yet understood.

Demographics

The exact number of people with the syndrome is not known, as some infants who die before or shortly after birth are never diagnosed or are diagnosed incorrectly. The syndrome affects males and females equally. There is no specific country or region of the world where the disorder is more common.

Signs and symptoms

In the bones of the lower arm (radius and ulna), limb shortening or absence of limbs is evident in approximately 97% of people with the syndrome. The upper arm (humerus) is affected 77% of the time. A missing or shortened thighbone (femur) occurs in about 65% of affected individuals. The bones in the lower leg (tibia and fibula) are shortened or absent in 77% of those with the disorder.

It is often very hard to flex or bend the knees, ankles, wrists, and/or elbows. While the feet and hands are almost always present, there may be fewer than normal fingers and toes, or shortened fingers. Sometimes the fingers are fused together (syndactyly).

People with the syndrome are smaller than other babies the same age, both before and after birth. Babies with Roberts SC phocomelia syndrome may have thin hair that is often described as silvery in color. In addition, most people with Roberts SC phocomelia syndrome are born with a cleft lip (a failure of the upper lip to close completely) and cleft palate (an opening in the roof of the mouth). Other abnormalities that may occur include a small and underdeveloped chin, a short neck, heart and kidney problems, prominent and widely spaced eyes, and unusually shaped ears.

Diagnosis

This disorder has been diagnosed during pregnancy at 12 weeks, through a test called an ultrasound evaluation. In these incidences, developmental problems with the growth and formation of both the arms and legs were noted. Sometimes the syndrome cannot be diagnosed by ultrasound until later in the pregnancy, when the limb shortening or absence becomes more obvious, and sometimes it cannot be diagnosed by ultrasound at all. Other abnormalities that might be seen by ultrasound include cleft lip, increased distance between the eye sockets, and extra fluid in some of the structures of the brain (hydrocephalus ). Excess amniotic fluid levels, kidney problems, and an opening in the spine (spina bifida ) have also been found. However, an exact diagnosis of the syndrome cannot be made by ultrasound evaluation alone.

Checking for the unusual chromosome feature is done through amniocentesis , a procedure that collects the developing fetus's cells for evaluation. But this test is not typically recommended, because not all affected individuals have this chromosome finding. In addition, the chromosome is not always evident in the cells from the amniotic fluid.

As of 2001 there was no accurate prenatal test to diagnose the syndrome during pregnancy.

After a baby is born with characteristics of Roberts SC phocomelia syndrome, a diagnosis can be made through a complete physical examination. In addition, analysis of the baby's chromosomes may also be useful. The chromosomes can be analyzed through a blood or tissue sample.

Treatment and management

At this time there is no treatment available for individuals with Roberts SC phocomelia syndrome. The shortness or absence of limbs makes it difficult for any type of limb-lengthening therapies to be useful in most instances.

Prognosis

The majority of severely affected individuals will die in the womb, or during or shortly after birth. Those who survive will have very obvious growth deficiency as well as mental retardation. Babies who are not as severely affected, with less dramatic limb shortening and no facial cleft, have a better overall prognosis.

Resources

BOOKS

Fleischer, A., et al. Sonography in Obstetrics and Gynecology, Principles & Practice. Stamford: 1996.

Jones, Kenneth. Smith's Recognizable Patterns of Human Malformations. 5th ed. Philadelphia: W.B. Saunders Company, 1997.

PERIODICALS

Camlibel, T. "Roberts SC Phocomelia with Isolated Cleft Palate, Thrombocytopenia, and Eosinophilia." Genetic Counseling 10, no. 2 (1999): 157–61.

McDaniel, L. D. "Novel Assay for Roberts Syndrome Assigns Variable Phenotypes to One Complementation Group." American Journal of Medical Genetics 93, no. 3 (2000): 223–9.

WEBSITES

"Entry 268300: Roberts syndrome; RBS." Online Mendelian Inheritance in Man.<http://www.ncbi.nlm.nih.gov/htbin-post/Omim/dispmim?268300>.

"Limb Anomalies." University of Kansas Medical Center.<http://www.kumc.edu/gec/support/limb.html>.

Katherine Susan Hunt, MS

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