Genetic Testing Specialist

Why are some genetic conditions more common in particular ethnic groups?

• Some genetic disorders are more likely to occur among people who trace their ancestry to a particular geographic area. People in an ethnic group often share certain versions of their genes, which have been passed down from common ancestors. If one of these shared genes contains a disease-causing mutation, a particular genetic disorder may be more frequently seen in the group.
• Examples of genetic conditions that are more common in particular ethnic groups are sickle cell anemia, which is more common in people of African, African-American, or Mediterranean heritage; and Tay-Sachs disease, which is more likely to occur among people of Ashkenazi (eastern and central European) Jewish or French Canadian ancestry. It is important to note, however, that these disorders can occur in any ethnic group.

What is Bloom Syndrome?

• Bloom syndrome is an inherited disorder characterized by a short and thin stature, sun-sensitive skin changes, and an increased risk of any of the cancers found in the general population. Cancers in people with Bloom syndrome arise unusually early in life, and affected individuals often develop more than one type of cancer.
• Other complications of this disease are learning disabilities, an increased risk of diabetes, chronic obstructive pulmonary disease (COPD), and recurrent infections of the upper respiratory tract, ears, and lungs during pregnancy. Men with Bloom syndrome usually do not produce sperm, and as a result are unable to father children (infertile). Women with the disorder generally have reduced fertility and experience menopause earlier than usual.

What is Canavan Disease?

• Canavan disease is an inherited disorder that causes progressive damage to nerve cells in the brain by degeneration of myelin, which is the fatty covering that insulates nerve fibers. The signs and symptoms of this disease usually begin in early infancy; however, the course of the condition can be quite variable. Infants with Canavan disease typically appear normal for the first few months of life. By age 3 to 5 months, affected infants begin having problems with development, including a delay in motor skills such as turning over, controlling head movement, and sitting without support. These infants typically also have weak muscle tone, unusually large head size, abnormal posture, and intellectual disability. Feeding and swallowing difficulties, seizures, and sleep disturbances may also develop. The life expectancy for people with Canavan disease varies. Most affected individuals live only into childhood, although some survive into adolescence and beyond.

What is Familial Dysautonomia?

• Familial dysautonomia is a genetic disorder that affects the development and survival of certain nerve cells. The disorder disturbs the cells in the autonomic nervous system, which controls involuntary actions such as digestion, breathing, production of tears, and the regulation of blood pressure and body temperature. The disorder also affects the sensory nervous system, which controls activities related to the senses, such as taste and the perception of pain, heat and cold?
• Problems related to this disorder first appear during infancy. Early signs and symptoms include poor muscle tone, feeding difficulties, poor growth, lack of tears, frequent lung infections, and difficulty maintaining body temperature. Older infants and young children with familial dysautonomia may hold their breath for prolonged periods of time, which may cause a bluish appearance of the skin or lips (cyanosis) or fainting. The breath-holding behavior usually stops by age 6. Developmental milestones, such as walking and speech, are usually delayed, although some affected individuals show no signs of developmental delay.
• Additional signs and symptoms in school-age children include bed wetting, episodes of vomiting, reduced sensitivity to temperature changes and pain, poor balance, abnormal curvature of the spine (scoliosis), poor bone quality and increased risk of bone fractures, and kidney and heart problems. Affected individuals also have poor regulation of blood pressure. They may experience a sharp drop in blood pressure upon standing, which can cause dizziness, blurred vision, or fainting. They can also have episodes of high blood pressure when nervous or excited, or during vomiting incidents. About one-third of children with familial dysautonomia have learning disabilities, such as short attention span that require special education classes. By adulthood, affected individuals often have increasing difficulties with balance and walking unaided. Other problems that may appear in adolescence or early adulthood include lung damage due to repeated infections, impaired kidney function, and worsening vision due to the shrinking size of optic nerves, which carry information from the eyes to the brain.

What is Gaucher disease?

• Gaucher disease is an inherited disorder that affects many of the body’s organs and tissues. The signs and symptoms of this condition vary widely among affected individuals. Researchers have described several types of Gaucher disease based on their characteristic features.
• Type 1 Gaucher disease is the most common form of this condition. Type 1 is also called non-neuropathic Gaucher disease because the brain and spinal cord (the central nervous system) are usually not affected. The features of this condition range from mild to severe and may appear anytime from childhood to adulthood. Major signs and symptoms include enlargement of the liver and spleen, a low number of red blood cells (anemia), easy bruising caused by a decrease in blood platelets, ling disease, and bone abnormalities such as bone pain, fractures, and arthritis.
• Types 2 and 3 Gaucher diseases are known as neuropathic forms of the disorder because they are characterized by problems that affect the central nervous system. In addition to the signs and symptoms described above, these conditions can cause abnormal eye movements, seizures, and brain damage. Type 2 Gaucher disease usually cause life-threatening medical problems beginning in infancy. Type 3 Gaucher disease also affects the nervous system, but tends to progress more slowly than Type 2.

What is Spinal Muscular Atrophy?

• Spinal muscular atrophy is a disorder that affects the control of muscle movement. It is caused by a loss of specialized nerve cells, called motor neurons, in the spinal cord and the part of the brain that is connected to the spinal cord (the brainstem). The loss of motor neurons leads to weakness and wasting (atrophy) of muscles used for activities such as crawling, walking, sitting up, and controlling head movement. In severe cases of spinal muscular atrophy, the muscles used for breathing and swallowing are affected. Spinal muscular atrophy is divided into subtypes based on the severity of the disease and the age when symptoms appear.
• Four types of spinal muscular atrophy affect children before the age of 1. Type 1 spinal muscular atrophy (also called Werdnig-Hoffman disease) is a severe form of the disorder that is evident at birth or within the first few months of life. Typically, affected infants have difficulty breathing and swallowing and are unable to sit without support.
• Type II spinal muscular atrophy is characterized by muscle weakness that develops in children between ages 6 and 12 months. Children with type II can sit without support, although they cannot stand or walk unaided.
• X-linked infantile spinal muscular atrophy has features that are very similar to Type I, except that children with this type are typically born with joint deformities that impair movement. In severe cases, affected infants are born with broken bones. Poor muscle tone before birth may contribute to the contractures and broken bones seen in these children.
• The fourth type of spinal muscular atrophy that appears in infancy is called distal spinal muscular atrophy type 1. This form of the disorder is characterized by progressive muscle weakness in the hands and feet that eventually spreads to the limbs. Affected individuals also develop paralysis of the muscles that separate the abdomen from the chest cavity (the diaphragm), which leads to respiratory failure. The signs and symptoms of distal spinal muscular atrophy type 1 typically appear between ages 6 weeks and 6 months. Rarely, people with this condition do not show symptoms until late childhood or adolescence.
• Three other types of spinal muscular atrophy can affect people in early childhood and adulthood. Type III spinal muscular atrophy (also called Kugelberg-Welander disease or juvenile type) is a milder form of the disorder than types I and II, or the X-linked form. Symptoms appear between early childhood and early adulthood. Individuals with type III spinal muscular atrophy can stand and walk unaided, but usually lose this ability later in life. Two types of spinal muscular atrophy, type IV and Finkel type usually occur after age 30. Symptoms of these adult-onset types of spinal muscular atrophy are typically mild to moderate and include muscle weakness, tremors and twitching.