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Correlagen Case Studies

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How genetic testing can help to diagnose an inherited disorder with certainty in patients
X-linked lymphoproliferative disease (XLP) is a rare, life-threatening inherited disorder. In patients with XLP, infection with Epstein-Barr virus (EBV) - the virus that causes mononucleosis (known as "mono") - can lead to an out-of-control immune response, usually resulting in death within days. XLP can be cured by bone marrow transplantation. However, XLP can be difficult to diagnose with certainty and bone marrow transplantation is too risky a procedure to be performed without a definite diagnosis of XLP. Genetic testing can provide such a definitive diagnosis of XLP.

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How genetic testing can help to differentiate between different forms of an inherited disorder in patients
Congenital hyperinsulinism (CH) is due to a malfunction of the parts of the pancreas that are involved in producing the hormone insulin. CH leads to dangerously low blood sugar levels in newborns and infants. This inherited disorder has been associated with genetic variations in any one of at least five different genes. Treatment depends on which gene is affected and on the nature of the genetic variation and can vary from drug therapy to partial or complete removal of the pancreas. These three therapies differ dramatically in their consequences for the patient. One form of the disease requires complete removal of the pancreas, often leading to life-long diabetes. Another form of the disease requires only partial removal of the pancreas and can be completely cured by this procedure. A third form of the disease can be controlled by drug treatment and does not require any surgery. Genetic testing can identify the specific genetic variation and thereby help the physician to determine which form of the disease is present and to select the best treatment.

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How genetic testing can identify carriers of a familial mutation
The following is a real-life "case study" of a patient for whom Correlagen performed genetic testing: The mother of an infant boy understood that she could have "carried" the inherited disease affecting her brother, X-linked agammaglobulinemia (XLA), to her son. XLA causes a defect in the immune system and makes patients extremely vulnerable to infections, which can lead to chronic lung disease or even be life-threatening. XLA typically only affects males, but can be "carried," ie, passed on, by females. Upon the advice of the baby's pediatrician, this mother therefore decided that her son's immunoglobulin levels should be tested, even though he had been reasonably healthy.

When the test results indicated that the baby's immunoglobulin levels were below normal, the baby was referred to an immunologist, who immediately started him on immunoglobulin replacement therapy in order to protect him from infections. The immunologist also ordered a genetic test for XLA. This test revealed the presence of an XLA-associated genetic variation in the baby’s genes, confirming a diagnosis of XLA.

The confirmation provided by the genetic test assured the family that immunoglobulin replacement therapy was the appropriate course of treatment for their baby. It also helped them to understand that their baby would need aggressive treatment, usually with antibiotics, whenever he got sick. Today, this baby boy is doing extremely well, and his long-term prognosis is very good. Early initiation of treatment allowed him to avoid the repeated infections that can lead to long-term problems such as chronic lung disease.

The mother is now also aware that she is a carrier of an XLA-associated genetic variation, and she knows the exact familial mutation. If she has other children, she can easily have them tested as infants to find out if they are affected – in the case of a boy – or a carrier – in case of a girl. She may also choose to let other members of her extended family, eg, her cousins, know about the familial mutation. Knowledge of the familial mutation may thus benefit this family through many generations.

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How genetic testing can identify at-risk and not-at-risk family members of patients with an inherited disease
The following is a typical scenario: A family with two sons is affected with hypertrophic cardiomyopathy (HCM), which is the most common inherited cardiac disease and is found in 1 of 500 persons. One son and the mother suffered sudden cardiac death, typical of HCM, and the other son has been diagnosed with the disease based on an echocardiogram. Between them, the two brothers have five young children. None of the children shows any symptoms or signs of HCM yet, but each child is at 50% risk of having inherited the disease from the father. Previously, each child would have undergone extensive cardiac exams at regular intervals for many years, since symptoms of the disease may first appear at any age and since detection of the characteristic changes is difficult. Diagnosis of the disease as early as possibly is very important, because it enables life-saving intervention to prevent sudden cardiac death.

Recently, the surviving brother decided to be genetically tested, and a disease-causing genetic variation was identified. The family tested each child for presence of the familial mutation. Two children harbor the familial mutation, three do not. The three children who do not harbor the familial mutation are not at increased risk of HCM, do not need to undergo costly cardiac screening, and can live completely normal lives. They can also be reassured that none of their descendants will be at increased risk of HCM. The two children who do harbor the familial mutation are at greatly increased risk of HCM, should receive regular cardiac screening, and should adhere to certain lifestyle changes to reduce the risk of sudden cardiac death. Given the fact that this familial mutation was associated with sudden cardiac death, an implantable cardioverting defibrillator (ICD) may also be considered for the affected children. New studies indicate that use of ICDs in properly selected patients with HCM is life saving.

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