Factors that increase your risk of thalassemia include:
1) Family history. Thalassemia is passed from parents to children through defective haemoglobin genes.
2) Ancestry The list of risk factors mentioned for Thalassemia in various sources includes: • Italian descent • Greek descent • Mediterranean descent • North African descent • South-East Asian descent • Chinese • Southern European In recent years, thalassemias have become more common in the United States, largely due to increasing numbers of immigrants from Southeast Asia.
Inheritance
Alpha Thalassemias
Four genes (two from each parent) are needed to make enough alpha globin protein chains. If one or more of the genes is missing, you will have alpha thalassemia trait or disease. This means that you don't make enough alpha globin protein. If you have only one missing gene, you're a silent carrier and won't have any signs of illness. If you have two missing genes, you have alpha thalassemia trait (also called alpha thalassemia minor). You may have mild anemia. If you have three missing genes, you likely will have hemoglobin H disease (which a blood test can detect). This form of thalassemia causes moderate to severe anemia. Very rarely, a baby will have all four genes missing. This condition is called alpha thalassemia major or hydrops fetalis. Babies with hydrops fetalis usually die before or shortly after birth.
Beta Thalassemias
Two genes (one from each parent) are needed to make enough beta globin protein chains. If one or both of these genes are altered, you will have beta thalassemia. This means that you don't make enough beta globin protein. • If you have one altered gene, you're a carrier. This condition is called beta thalassemia trait or beta thalassemia minor. It causes mild anemia. • If both genes are altered, you will have beta thalassemia intermedia or beta thalassemia major (also called Cooley's anemia). The intermedia form of the disorder causes moderate anemia. The major form causes severe anemia.
Inheritance patterns:
There are various clear patterns common to any autosomal recessive genetic disease:
· Children of an affected person will typically not have the disease (except in the rare case that they too marry someone who is also affected or a carrier of exactly the same disease), but the odds are 100% the child will be a carrier. The affected parent has two bad copies of the gene, so the child gets a bad gene from that parent, but usually a good second copy from the other unaffected parent.
· If only one parent is a carrier (and the other unaffected), the child cannot get the disease, but might still be a carrier (typically 50% chance of being a carrier).
· If both parents are a carrier, there is a 25% chance that their child will have the disease. There is also a 50% chance the child will be a carrier, and only 25% chance the child will be neither diseased nor carrier. The situation where both parents are carriers is the most likely way that children with the disease are born.
· If one parent has the disease, and the other is a carrier, a child has a 50% chance of getting the disease, and 50% chance of being a carrier. The child definitely gets one bad gene from the diseased parent, and has a 50% chance of getting a second one from the carrier parent.
· Other children: If parents have one affected child, the odds of a second are usually 25%. If parents have a child with the disease, this almost always means that they are both carriers. The chances a second child will also have the disease are the same as above for two parent carriers: 25% chance of disease, 50% chance the second child is a carrier, and 25% chance of neither disease nor carrier. Note that genetic testing can often detect the rarer case where a child gets a genetic disease without both parents being carriers (perhaps only one is a carrier).
· Gender bias: Male or females get the disease equally, because an autosomal error is unrelated to the sex chromosomes. · Inheritance patterns tend to be "horizontal", which a generation being affected (i.e. many siblings of the same parents), but not their parents nor their own children. Parents and next-generation children will usually be carriers.
Sporadic cases: A genetic disease that occurs when neither parent has any genetic defect is called asporadic genetic disease. These cases arise via random genetic mutations in the DNA. A sporadic genetic mutation is not likely as a cause of an autosomal recessive disease, because it would require two identical random mutations (one in each copy of the gene) at the same time.
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