Asplenia

Definition

The term "asplenia" literally means absent spleen. However, in the condition asplenia, the spleen is not always absent. Sometimes the spleen is present, but not fully developed (hypoplastic). In asplenia, the spleen is typically not the only organ affected. Individuals with this condition often have problems with other organs and organ systems. A related condition is polysplenia. The term "polysplenia" literally means multiple spleens. Both of these conditions affect the placement and development of the organs inside the body. There is controversy over whether asplenia and the other syndromes, like polysplenia, that affect the position of the internal organs are actually different aspects of the same condition, referred to as Heterotaxy syndrome, or separate and distinct syndromes. As of 2001, this issue has not been resolved.

Asplenia is just one of the names used to refer to this condition. Other names include Ivemark syndrome, right isomerism sequence, bilateral right-sideness sequence, splenic agenesis syndrome, and asplenia with cardiovascular anomalies.

Description

The human body can be viewed as having a right side and a left side. Normally, inside the human body, the right side and the left side are different with respect to the presence of certain organs. Several organs inside the body are placed asymmetrically, meaning that one organ may be located on one side of the body, but not the other. Furthermore, there are some organs that are found on both sides of the body, but have differences that distinguish the right organ from its partner on the left side. In asplenia, the position, location, appearance, and performance of some of the internal organs are altered. Organs can often be found on the wrong side of the body and/or have structural defects. Furthermore, in most people the right and left organs are different; in people with asplenia, both organs may appear to be structured the same.

Genetic profile

In most families, asplenia is believed to occur sporadically. In other words, it occurs for the first time in a family and has no known or identifiable pattern of inheritance .

There have been several couples described in the medical literature who have more than one child diagnosed with asplenia. In several of these families, the parents were related to each other. Individuals who are related to each other are more likely to carry some of the same non-working genes. Therefore, these families illustrate the possibility that asplenia can be inherited in an autosomal recessive manner. Individuals who have an autosomal recessive condition have both genes in a pair that do not work as expected or are missing, thereby causing the disease. One non-working gene is inherited from the mother and the other is inherited from the father. These parents are called carriers of that condition. When two people are known carriers for an autosomal recessive condition, they have a 25% chance with each pregnancy of having a child affected with the disease.

There are a few families where asplenia appears to be inherited in an autosomal dominant or X-linked manner. In autosomal dominant inheritance, only one gene in the pair needs to be abnormal to cause symptoms of the condition. In families where asplenia appears to be inherited in an autosomal dominant manner, family members who carry the same non-working gene can have different symptoms and the severity of the condition may vary. In autosomal dominant inheritance, if an individual carries the non-working gene, he or she has a 50% chance of passing the gene on with each pregnancy.

In families where asplenia appears to be inherited in a X-linked manner, the gene causing the condition is located on the X chromosome. Since women have two X chromosomes , if a woman inherits the non-working gene on one of her X chromosomes, typically she will not have any symptoms of asplenia or will have a milder form of the condition. A woman who carries the X-linked form of asplenia will have a 50% chance of passing that non-working gene on with each pregnancy.

Since men tend to have one Y chromosome and one X chromosome, if it is a son that inherits the non-working gene, he will be affected with the condition. Men who have a X-linked form of asplenia will always pass their X chromosome containing the non-working gene on to all of their daughters, who would be carriers of the condition. In these families, asplenia will never be passed from the father to the son, since men give their sons a Y chromosome. If a woman who carries a X-linked condition passes the X chromosome containing the non-working gene to a daughter, then that daughter will be a carrier like her mother.

The pattern of inheritance of asplenia in a family is usually not obvious when there is only one individual diagnosed with the condition. Based on the families and studies performed on asplenia, the chance of a couple who have one child with asplenia having another child with the condition is approximately 5% or less. This chance may be higher if it is determined that asplenia is part of Heterotaxy syndrome, since there are a wider range of symptoms associated with that condition. Furthermore, if more than one family member has the diagnosis of asplenia, the chance of it occurring again in the family is based on the pattern of inheritance that the condition appears to be following.

Since asplenia appears to be inherited in different ways, it is theorized that there may be several different genes that could cause asplenia. This means that some families may have asplenia caused by one specific nonworking gene, but in other families, a different non-working gene could cause the same condition to occur. As of 2001, the exact genes involved in causing asplenia have not been identified. However, there is ongoing research to identify the genes involved with this condition.

Demographics

It is estimated that the incidence of asplenia is low, approximately one in 10,000 to one in 20,000 live births. More males are affected with the condition than females. Asplenia also accounts for 1-3% of all congenital heart defects . Asplenia does not appear to occur more frequently in certain ethnic groups.

Signs and symptoms

Almost all individuals with asplenia have an abnormal or absent spleen. However, there are other organs and organ systems that can be affected.

Abdominal organs

SPLEEN As the name of the condition implies, the spleen is always affected in asplenia. The spleen in individuals with asplenia is either absent or does not develop completely (hypoplastic spleen). Since the spleen is involved in the body's immune system, these infants can have an abnormal immune system, which increases their risk for developing an infection.

DIGESTIVE TRACT DISORDERS There are several abnormalities that can occur with the digestive tract in individuals with asplenia. The most common digestive tract disorder associated with asplenia is malrotation of the intestine. Sometimes a digestive tract problem will present with symptoms of an obstruction in the digestive system, requiring emergency surgery.

STOMACH Most individuals with asplenia have their stomach located on the right side or in the center of the body instead of the left. In addition, individuals with asplenia can have a "twisted" stomach that could result in an obstruction in their digestive system and impair the blood supply to the stomach (gastric volvulus).

LIVER Normally, the liver is located on the right side of the body and the shape of the liver is not symmetrical. In asplenia, there can be isomerism of the liver—it can be located in the middle of the body, or located on the left side with the larger half of the liver located in the upper left side of the abdominal area.

GALLBLADDER The gallbladder may also be located in the middle of the body in individuals with asplenia.

Heart

Many infants with asplenia first present with cyanosis and severe respiratory distress. These are symptoms often seen in individuals who have a heart defect. Most individuals with asplenia have a defect in the structure and/or the position of their heart.

Typically, the heart is divided into two sides, a left and right, with each side containing two chambers, called ventricle and atrium. The left and right sides of the heart are different from each other in their structure and function. The job of the right side of the heart is to pump blood to the lungs to receive oxygen. The job of the left side of the heart is to receive the oxygenated blood from the lungs and pump it to the rest of the body. In asplenia, sometimes the structures of the right side of the heart are duplicated on the heart's left side.

A common heart defect often seen in asplenia is anomalous pulmonary venous return, which occurs when the pulmonary veins (the blood vessels that carry blood containing oxygen from the lungs to the heart) are connected to the right atrium instead of the left atrium. This causes the oxygenated blood to be pumped back to the lungs instead of the body. Sometimes, there is a hole between the right and left atrium (called atrial septal defect or ASD) that allows some of the oxygenated blood into the left atrium and pumped to the rest of the body.

Other heart defects frequently seen in individuals with asplenia include: common atrioventricular canal, common atrial canal, persistent truncus arteriosus, pulmonary stenosis or atresia, single ventricle in the heart, and transposition of the great arteries. Often there is more than one heart defect present. Furthermore, in many individuals with asplenia, the heart is located on the right side of the body instead of the left.

Lungs

Normally, the lungs are divided into lobes. The lung on the right side of the body usually has three lobes and the left lung typically has two lobes. In asplenia, each lung usually has three lobes.

There can be abnormalities in other systems of the body as well, but they are not often seen in most individuals with asplenia. Other abnormalities associated with asplenia include kidney anomalies, extra fingers and toes, scoliosis , facial abnormalities, and central nervous system anomalies.

Diagnosis

The diagnosis of asplenia is typically made by imaging studies. An echocardiogram of the heart can help identify any structural abnormalities and its exact position within the body. A chest x ray can also be used to locate the position of the heart and some of the other organs in the body. Ultrasound and CT examinations can also help determine if there are any malformations with the abdominal organs, the position of the stomach, the presence, appearance, and number of spleens, and how many lobes each lung has. While a MRI can also detect the presence and position of organs inside the body, it is less commonly used because of the need for sedation and the high cost of the test, especially in children.

Testing for the presence of Heinz and Howell-Jolly bodies in the blood has been suggested as a method to screen for an absent spleen. Howell-Jolly bodies are unique cells that tend to be present in the blood of individuals who do not have a spleen, but they can also be seen in the blood of individuals who have certain types of anemia. Therefore, this test should not be used as the sole diagnostic test for an absent spleen.

Some of the abnormalities seen in asplenia can be detected prenatally. Often the position of the heart and some of the heart defects can be diagnosed by fetal echocardiogram (an ultrasound examination of the fetal heart) in the late second and third trimesters of pregnancy. A fetal echocardiogram should be performed during pregnancy when a couple already has a child with asplenia. Additionally, a level II ultrasound examination can detect some digestive system anomalies, such as the position of the stomach.

Treatment and management

Surgery can sometimes be performed on the heart to repair the defect or defects. There are limitations to heart surgery and it cannot always be performed. Additionally, heart surgery is not always successful. Surgery can also be used to correct many of the digestive tract disorders.

Additionally, because the spleen is involved in the body's immune system, it is recommended that all patients with the diagnosis of asplenia be given antibiotics and pneumococcal vaccination.

Prognosis

Without treatment, the prognosis of an infant diagnosed with asplenia is poor, with approximately 80% of these infants dying within the first year of life. The cause of death is usually complications from the heart defect. However, with advances in heart surgery and improvements in correcting many of the digestive tract anomalies, infants with asplenia are living much longer.

Resources

PERIODICALS

Applegate, K., et. al. "Situs Revisited: Imaging of the Heterotaxy Syndrome." RadioGraphics 19 (1999): 837-52.

Nakada, K., et. al. "Digestive Tract Disorders Associated with Asplenia/Polysplenia Syndrome." Journal of Pediatric Surgery 32 (1997): 91-94.

Splitt, M. P., et. al. "Defects in the Determination of Left-Right Asymmetry." Journal of Medical Genetics 33 (1996): 498-503.

ORGANIZATIONS

Ivemark Syndrome Association. 52 Keward Ave., Wells, Somerset, BAS-1TS. UK 1-(74)967-2603.

WEBSITES

Gee, Henry. "The Sources of Symmetry." Nature: ScienceUpdate. (1998) <http://www.nature.com.nsu/980806/980806-7.html>.

"OMIM# 208530: Asplenia with Cardiovascular Anomalies." OMIM—Online Mendelian Inheritance in Man. <http://www.ncbi.nih.gov/htbin-post/Omim/dispmim?208530>. (May 14 1999).

Sharon A. Aufox, MS, CGC