Roberts syndrome


Roberts syndrome, or sometimes called pseudothalidomide syndrome, is an extremely rare autosomal recessive genetic disorder that is characterized by mild to severe prenatal retardation or disruption of cell division, leading to malformation of the bones in the skull, face, arms, and legs.
It is caused by a mutation in the ESCO2 gene. It is one of the rarest autosomal recessive disorders, affecting approximately 150 known individuals. The mutation causes cell division to occur slowly or unevenly, and the cells with abnormal genetic content die.
Roberts syndrome can affect both males and females. Although the disorder is rare, the affected group is diverse. The mortality rate is high in severely affected individuals. The syndrome is named after American surgeon and physician John Bingham Roberts, who first described it in 1919.

Symptoms

The following is a list of symptoms that have been associated with Roberts syndrome:
Mortality is high among those severely affected by Roberts syndrome; however, mildly affected individuals may survive to adulthood

Heredity

, located on human chromosome 8, has been labeled as the gene responsible for Roberts syndrome. In fact, ESCO2 is the only known gene that has demonstrated RBS-causing mutations. Also, all individuals that have been cytogenetically diagnosed with Roberts syndrome have also had mutations in the ESCO2 gene.
In order to contract Roberts syndrome, a child must inherit the defective gene in an autosomal recessive manner. In other words, the child must inherit two copies of the defective gene. The ESCO2 gene has a specific effect on cell division in Roberts syndrome patients. In normal cell division, each chromosome is copied and then attached to its newly formed copy at the centromere. However, in Roberts syndrome cell division, the copies are frequently not attached at the centromere. As a result, the chromosomes do not get lined up properly, which causes the cell to divide very slowly or even to not divide at all. The new cells typically will have too many or too few chromosomes. The odd number of chromosomes causes the defective cells to die, which leads to the malformations associated with Roberts syndrome.
Many of the physical malformations associated with Roberts syndrome are very similar to the malformations that occur in children whose mothers took thalidomide during pregnancy. The physical similarities suggest that there is a similar underlying biology between ESCO2 and thalidomide. As a result, it is speculated that thalidomide affects chromosomes and cell division in a similar manner to ESCO2. For this reason, Roberts syndrome is sometimes called Pseudothalidomide Syndrome.

Discovery of the syndrome

The discovery of ESCO2 as the gene responsible for Roberts syndrome was made by studying samples from fifteen families affected by Roberts syndrome. In 1995, Hugo Vega and Miriam Gordillo, two Colombian geneticists, set out to fully understand Roberts syndrome. Vega and Gordillo noticed an unusually high number of Roberts syndrome patients at the Universidad Nacional de Colombia. The two Colombian geneticists tracked down a total of seven families with Roberts syndrome just outside Bogota and discovered that four out of the seven families shared a common 18th century ancestor. Using this information, Vega and Gordillo were able to pinpoint the gene responsible for Roberts syndrome, which was ESCO2.

Diagnosis

Clinical diagnosis

A clinical diagnosis of Roberts syndrome is made in individuals with characteristic prenatal growth retardation, limb malformations, and craniofacial abnormalities. The specific characteristics that are looked for in the clinical diagnosis are listed below.
An official diagnosis of Roberts syndrome relies on cytogenetic testing of the peripheral blood.

Testing

Cytogenetic testing

Cytogenetic preparations that have been stained by either Giemsa or C-banding techniques will show two characteristic chromosomal abnormalities. The first chromosomal abnormality is called premature centromere separation and is the most likely pathogenic mechanism for Roberts syndrome. Chromosomes that have PCS will have their centromeres separate during metaphase rather than anaphase. The second chromosomal abnormality is called heterochromatin repulsion. Chromosomes that have HR experience separation of the heterochromatic regions during metaphase. Chromosomes with these two abnormalities will display a "railroad track" appearance because of the absence of primary constriction and repulsion at the heterochromatic regions. The heterochromatic regions are the areas near the centromeres and nucleolar organizers. Carrier status cannot be determined by cytogenetic testing. Other common findings of cytogenetic testing on Roberts syndrome patients are listed below.
At this point in time, ESCO2 is the only known gene to cause Roberts syndrome mutations. Also, all individuals that have been diagnosed with Roberts syndrome by cytogenetic techniques have also had ESCO2 mutations. Confirmation of a Roberts syndrome diagnosis requires detection of the characteristic chromosomal abnormalities or the identification of two ESCO2 mutations that have been linked to Roberts syndrome.

Carrier testing and prenatal diagnosis

Carrier testing for Roberts syndrome requires prior identification of the disease-causing mutation in the family. Carriers for the disorder are heterozygotes due to the autosomal recessive nature of the disease. Carriers are also not at risk for contracting Roberts syndrome themselves. A prenatal diagnosis of Roberts syndrome requires an ultrasound examination paired with cytogenetic testing or prior identification of the disease-causing ESCO2 mutations in the family.

Genetically related disorders

At this time, there are no other phenotypes that have been discovered for mutations in the ESCO2 gene.

Differential diagnosis

In cases of mild malformations, the following disorders should be considered in the differential diagnosis:
In cases of severe manifestations, the following disorders should be considered in the differential diagnosis:
In cases of similar cytogenetic findings, the following disorders should be considered in the differential diagnosis:
Little is known about the natural history of Roberts syndrome due to its wide clinical variability. The prognosis of the disease depends on the malformations, as the severity of the malformations correlates with survival. The cause of death for most fatalities of Roberts syndrome have not been reported; however, five deaths were reportedly due to infection.
The following are observations that have been made in individuals with cytogenetic findings of PCS/HR or ESCO2 mutations:
Treatment of Roberts syndrome is individualized and specifically aimed at improving the quality of life for those afflicted with the disorder. Some of the possible treatments include: surgery for the cleft lip and palate, correction of limb abnormalities, and improvement in prehensile hand grasp development.

Prevalence

Roberts syndrome is an extremely rare condition that only affects about 150 reported individuals. Although there have been only about 150 reported cases, the affected group is quite diverse and spread worldwide. Parental consanguinity is common with this genetic disorder. The frequency of Roberts syndrome carriers is unknown.

Nomenclature

Roberts Syndrome is named after Dr. John Bingham Roberts of Philadelphia, who reported the disease characteristics in 1919. Roberts reported a disease that was characterized by phocomelia, cleft lip, cleft palate, and a protrusion of the intermaxillary region in three siblings of an Italian couple. The Italian couple were first cousins, which made Roberts Syndrome acquisition more likely for their children due to the diseases autosomal recessive nature.
Later, in 1969, J. Herrmann described another syndrome with very similar characteristics to Roberts syndrome. Herrmann would call the disorder Pseudothalidomide Syndrome or SC Syndrome. Today, Roberts Syndrome and Pseudothalidomide Syndrome are considered to be the same disorder.
The following is a list of all the alternate names that have been used for Roberts Syndrome: