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The goal of this article is to describe the major features of 18p-. This information was obtained from a thorough review of the literature as well as from the experiences of the Chromosome 18 Clinical Research Center. This information may help you and your health care team make decisions about how to care for a person with 18p-.
As you read through this article, remember that no two people with 18p- are exactly alike. One person may have different medical and developmental concerns from another person with 18p-. Also, remember that no one with 18p- will have all of the features discussed below. In addition, people with 18p- share many features with their family members. They will also have their own unique skills and abilities which you will not find in the following list.
Lastly, research is critical. As we learn more about 18p-, we also learn more about how to best treat it. This will improve the health and development of people with 18p-.
18p- was first described in the 1960s. Since then, over 100 case reports have been published, describing the features of 18p-.
18p- has been called several different names. You may hear this condition called “monosomy 18p” , “18p deletion syndrome”, or “18p- syndrome”.
Genetic Basis of 18p-
The term “18p-” means that part or all of the short arm of chromosome 18 is missing, or deleted, from one of the two copies of chromosome 18. For more information about basic genetic concepts, please review our section on genetics.
Below is a diagram showing the difference between a normal pair of chromosome 18's and one with a deletion of the short arm.
The loss of part of the short arm of the chromosome causes 18p-. The deletion may include the entire short arm of chromosome 18 or only a part of the arm.
In most individuals, the deletion is the only chromosome change present. However, in some cases, the deletion results from a more complicated chromosome rearrangement. For example, some people have 18p- because of an unbalanced translocation. An unbalanced translocation may lead to 18p- and a duplication of another piece of chromosome. In this case, predicting what type of problems a child might have is more difficult. People with an unbalanced translocation may have features of 18p- as well as features of the chromosome duplication.
Characteristics of 18p-
For a table with the frequency of various medical and developmental concerns reported in individuals with 18p-, please click here.
In many individuals, 18p- changes the way the brain develops and works.
Infants, toddlers and young children with 18p- may develop more slowly than those without 18p-. For example, it may take a little longer for them to roll over, sit, crawl, and walk. It may also take longer for them to reach for and grab toys, hold a bottle, and to feed themselves. Language skills also develop later than their peers. Almost all children with 18p- will require some type of therapy, such as speech, occupational, or physical therapy.
People with 18p- may have some cognitive disability, though the degree of impairment varies among individuals. Based on standardized testing, people with 18p- appear to have IQ scores ranging from average to severe mental impairment.
People with 18p- may also have some challenges with adaptive skills. The phrase "adaptive skills” refers to a person’s social skills as well as their level of independence. In the case of 18p-, a person’s IQ may not be directly related to their adaptive skills. Often a person’s adaptive skills are higher than their IQ score might suggest.
It is important to remember that every person with 18p- is different. Some may be more severely affected than others. At this time, we cannot predict exactly how a deletion of 18p will affect a child’s development.
Some people with 18p- have a condition called holoprosencephaly. Holoprosencephaly is a type of birth defect in which the brain fails to divide into two separate halves during early embryonic development. This term includes a wide range of severity. In some babies, this condition is so severe that they do not survive in the womb or they may die shortly after birth.
Other individuals may have milder forms of the condition. For example, an MRI may show that their brain has minor changes, such as a missing corpus callosum (the connection between the two halves of the brain). There may be changes in the facial features as well, such as a cleft lip and palate or hypotelorism (eyes that are closely set to one another). Another minor feature of holoprosencephaly is a single incisor (front tooth) located at the midline of the mouth.
Individuals with holoprosencephaly may have a number of different health concerns. Many have developmental delays. Seizures and hydrocephalus (build-up of fluid in the brain) may also occur. Some people with holoprosencephaly may have hormone problems caused by a change in the structure of the pituitary gland in the brain.
To learn more about holoprosencephaly, you can visit the National Institute of Neurological Disorders and Stroke.
People with 18p- may have neurological problems that are unrelated to the presence or absence of holoprosencephaly. For example, they may have low muscle tone (hypotonia). Seizures have also been diagnosed in a small number of people with 18p-. Children with holoprosencephaly have a higher likelihood of having seizures.
Dystonia has been reported in a handful of people with 18p-. Dystonia is an involuntary contraction of muscles. Because the muscles cannot relax, people with dystonia may have changes in their posture due to dystonia. Tethered cord has also been reported in some people with 18p-. A tethered cord occurs when the spinal cord is attached to the bony part of the spine. This can lead to bowel and bladder problems as well as back pain or curvature of the spine.
If there are neurological concerns, a person may be referred to a neurologist for a complete evaluation. If there is a concern of seizures, a primary care physician or a neurologist may request an electroencephalogram (EEG).
Eyes and Vision
Vision problems are often found in people with 18p-. Near-sightedness and far-sightedness are fairly common. Also, the eyes may be misaligned (strabismus). Another common eye problem is ptosis. Ptosis occurs when the eyelid droops. In some cases, ptosis can cause problems with vision by covering the eye. When this happens, a person’s vision is reduced.
Because vision problems are possible, people with 18p- should have regular eye exams. In some cases, surgery may be required to treat strabismus or ptosis.
Babies, toddlers, and children with 18p- may have more ear infections than other children. Ear infections may lead to hearing problems if left untreated. Therefore, it is important to identify and treat ear infections. Most of the time, medicine is prescribed to treat the ear infection. Some children may require surgery to insert tubes in the ears to reduce the number of ear infections.
Because there is a risk for hearing loss due to the ear infections, people with 18p- should have regular hearing screening. This will help find and treat hearing loss early.
Cleft Lip and Palate
Cleft lips and palates are more common in babies with 18p- than in the general population. The palate is the roof of the mouth. Sometimes the palate does not form correctly during development. This results in an opening in the roof of the mouth. A cleft lip occurs when the tissue that forms the upper lip does not fuse during prenatal development. Cleft lip and palate may lead to dental, hearing, speech, and feeding problems.
In most cases, a team of professionals is involved in the management of cleft lip and palate. This team may include surgeons, speech pathologists, dentists, audiologists, geneticists, and other professionals. To locate a team in your area, contact the Cleft Palate Foundation.
Heart defects are found in about 25% of babies with 18p-. There are several different kinds of heart defects that have been diagnosed in babies with 18p-. There doesn’t appear to be a specific type of heart defect that is more commonly associated with 18p-.
Because heart defects are more common in babies with 18p- than in those without 18p-, an echocardiogram (ultrasound of the heart) may be recommended to look for defects.
Gastrointestinal and Other Abdominal Changes
Babies and children with 18p- may have some problems with digestion. The most common digestive problem is chronic constipation. A physician may prescribe dietary changes or medication to help manage constipation.
Hernias may also occur in babies with 18p-. A hernia occurs when some organs, often the intestines, push outside of the abdomen. This problem is usually corrected by surgery.
There have been a very limited number of reports in the scientific literature of people with 18p- and a rearrangement of their internal organs or additional organs. For example, in one individual, the location of the internal organs was reversed (situs inversus). In other individuals, there was an extra spleen (accessory spleen), or a malrotation of the intestines. In these case reports, the changes did not require surgical correction. It should be noted, however, that these types of malformations may require surgical intervention on occasion.
Males with 18p- may have some changes in the genital region. The testicles may not be fully descended (cryptorchidism). The opening of the urethra may not be at the end of the penis (hypospadias). In some cases, surgery may be required to correct these concerns.
Foot abnormalities are fairly common in people with 18p-. Their feet may be rotated inward or outward. They may also have flat feet.
People with 18p- may have “bow-leggedness” (genu varum). They may also develop an abnormal curvature of their spine. All of these bone problems can affect the way they walk and may lead to gait abnormalities.
People with foot, knee, or spinal changes may be referred to an orthopedic specialist by their regular medical doctor. Braces and inserts, surgery, and therapy may help in addressing orthopedic concerns.
Children and adults may have changes in their growth patterns. Children with 18p- are often small for their age. In some cases, this is due to growth hormone deficiency. Growth hormone deficiency has been reported frequently within the literature as well as by research participants at the Chromosome 18 Clinical Research Center.
If there is a concern regarding growth, a person can see a pediatric endocrinologist to rule out growth hormone deficiency. Drs. Jannine Cody and Daniel Hale have written an article for the Chromosome 18 Registry & Research Society about growth hormone deficiency in children with 18p-.
In addition to short stature, many people with 18p- have microcephaly, or a head size that falls below the 3rd percentile.
Some people with 18p- have thyroid problems. Thyroid hormones regulate a number of functions in the body, including how fast the heart beats and how quickly a person burns calories. Some signs of low thyroid hormone include fatigue, weight gain, and depression.
People with 18p- should be screened for thyroid problems once a year. This is because thyroid problems can arise at any time in their life. This screening can be done through an annual blood test. If a thyroid problem is found, an endocrinologist may prescribe medications to treat the problem.
Low levels of IgA are found in some people with 18p-. IgA is a protein that helps fight off infections. People who have a low level of IgA are more likely to get infections and colds that those with normal levels of IgA. For example, they may have lots of ear and sinus infections.
In most cases, IgA deficiency is managed by treating infections, allergies, and asthma early.
People with18p- may have facial features that are slightly different from other family members. These changes do not affect a child’s health or development. They are simply small differences that might be noted by a doctor.
For example, people with 18p- may have ears that are lower-set and look slightly different from a “typical” ear. They may have an extra fold of skin covering the corner of the eye. The lower jaw may be slightly smaller than in people without 18p-.
Although people with 18p- may have facial features in common with one another, it is important to remember that they also have features in common with their family members.
When a child is diagnosed with 18p-, one of the family’s first questions is often, “What does this mean for my child’s lifespan?” This is a very important question. In general, if a person with 18p- is in good health with no major birth defects, there is no reason that they should not live to adulthood. Within the Chromosome 18 Clinical Research Center 18p- population, there has been one person that has died. This patient passed away at 13 years old due to complications following cardiac surgery. It is important to remember that early death in this population is the exception rather than the rule.
Family Planning and Genetic Counseling
Many parents wonder, “If we have another child, what is the chance that our next child will have 18p-?”
The answer to this question depends on whether a chromosome change has been identified in one of the parents. In most cases, neither parent has a chromosome change. In this situation, the chance that a couple will have another child with 18p- is very low.
In a small number of families, one parent has an 18p deletion. If a parent has a deletion, there is a 50% chance that they will have a child with 18p-.
In some families, the deletion of 18p results from a more complicated chromosome rearrangement in a parent, such as a translocation. In this situation, the likelihood that another child would have a chromosome change depends on what type of rearrangement the parent has and which chromosomes are involved.
If you have questions about the implications of a chromosome change for other family members, we recommend contacting a genetics provider.
For Additional Information
The information provided here is general information based on the literature as well as the experiences in the Chromosome 18 Clinical Research Center. However, every person with 18p- is different. Therefore, this information should not replace professional medical advice, diagnosis, or treatment. If you have questions or concerns, you may find it helpful to talk with a clinical geneticist or genetic counselor. You can locate a genetics provider at one of these sites:
GeneTests Clinic Directory
National Society of Genetic Counselors
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