The mutations can come as;<\/p>\n\n\n\n
- One gene i.e monogenic disorders<\/strong> such as cystic fibrosis<\/em><\/li>
- Many genes i.e polygenic <\/strong>and also influenced by the environment i.e multifactorial (multiple factors) disorders<\/strong> such as Alzheimer’s disease<\/div><\/li><\/ul>\n\n\n\n
There are two types of mutations(based on what type of proteins they affect) that can cause genetic diseases:<\/p>\n\n\n\n
- Mutations in proteins expressed in all cells of the body<\/li>
- Mutations in proteins expressed in certain tissues of the body<\/li><\/ol>\n\n\n\n
Mutations in proteins expressed in all cells of the body<\/h4>\n<\/span>\n\n\n
- These are housekeeping protein<\/strong> mutations.<\/li>
- They are called housekeeping proteins because they have basic and regulatory functions in all cells of the body.<\/li>
- The phenotypic expression of these mutations is seen in a few tissues.<\/li>
- An example is Lysosomal storage disorders (lysosomal genes are housekeeping genes; we need lysosomes in all body cells)<\/li><\/ul>\n\n\n<\/span>\n
Mutations in proteins expressed in certain tissues of the body<\/h4>\n<\/span>\n\n\n
- The phenotypic expression of these mutations is seen in a lot of tissues; those directly affected by the mutation and those that are not.<\/li>
- An example is Phenylketonuria.<\/li><\/ul>\n\n\n\n
In this section, we will discuss the diseases based on inheritance patterns<\/strong>:<\/p>\n\n\n\n
- Autosomal dominant diseases<\/li>
- Autosomal recessive diseases<\/li>
- X linked dominant diseases<\/li>
- X linked recessive diseases<\/li><\/ul>\n\n\n\n
Since there are a lot of autosomal recessive diseases, we will discuss them in two parts; I and II. Details on inheritance patterns are discussed in the Transmission Genetics: Single Gene disorders course<\/em><\/p>\n\n\n\n
As we will be discussing haemoglobinopathies <\/strong>(a group of diseases that affect red blood cells)<\/em> here, it is appropriate for us to start with the structure of haemoglobin.<\/p>\n\n\n<\/span>\n
Structure of haemoglobin<\/h4>\n<\/span>\n\n\n
Haemoglobin is the molecule in red blood cells that allows them to do their most important function; transport of oxygen around the entire body.<\/p>\n\n\n\n
It is made up of two parts;<\/p>\n\n\n\n
- Heme<\/strong> — A coordination complex containing four porphyrin rings with Iron II (Fe2+) in the center<\/li>
- Globin<\/strong> — A polypeptide chain.<\/li><\/ul>\n\n\n\n
There are three main forms of haemoglobin;<\/p>\n\n\n\n
- Fetal haemoglobin<\/li>
- Adult haemoglobin A<\/li>
- Adult hemoglobin A2<\/li><\/ol>\n\n\n<\/span>\n
Fetal haemoglobin<\/h4>\n<\/span>\n\n\n
- Also known as HbF<\/strong>, it contains two alpha and two gamma chains<\/li><\/ul>\n\n\n<\/span>\n
Adult haemoglobin A<\/h4>\n<\/span>\n\n\n
- This is the first form of haemoglobin found in adults.<\/li>
- It is found in 95%-98% of the red blood cells present in a person.<\/li>
- It is also known as HbA <\/strong>and it contains two alpha and two beta chains<\/li><\/ul>\n\n\n<\/span>\n
Adult haemoglobin A2<\/h4>\n<\/span>\n\n\n
- This is the second form of haemoglobin found in adults.<\/li>
- It is found in 2%-5% of the red blood cells present in a person.<\/li>
- It is also known as HbA2<\/strong> and it has two alpha and two delta chains<\/li><\/ul>\n\n\n\n
- Also known as HbF<\/strong>, it contains two alpha and two gamma chains<\/li><\/ul>\n\n\n<\/span>\n
- Globin<\/strong> — A polypeptide chain.<\/li><\/ul>\n\n\n\n
- Heme<\/strong> — A coordination complex containing four porphyrin rings with Iron II (Fe2+) in the center<\/li>
- These are housekeeping protein<\/strong> mutations.<\/li>
- Many genes i.e polygenic <\/strong>and also influenced by the environment i.e multifactorial (multiple factors) disorders<\/strong> such as Alzheimer’s disease<\/div><\/li><\/ul>\n\n\n\n
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