GENETIC DISORDERS

Hi students:

This week yo will design an oral presentation about Genetic disorders. So please, read the following information and follow the class instructions to make it.

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• What is a genetic disease? How is it defined?

 A genetic disease is any disease that is caused by an abnormality in an individual's genome, the person's entire genetic makeup. The abnormality can range from minuscule to major -- from a discrete mutation in a single base in the DNA of a single gene to a gross chromosome abnormality involving the addition or subtraction of an entire chromosome or set of chromosomes. Some genetic disorders are inherited from the parents, while other genetic diseases are caused by acquired changes or mutations in a preexisting gene or group of genes. Mutations can occur either randomly or due to some environmental exposure.

What are the types of genetic inheritance?

There are a number of different types of genetic inheritance including:

• Single gene inheritance
• Multifactorial inheritance
• Chromosome abnormalities
• Mitochondrial inheritance

Single gene genetic inheritance

Single gene inheritance, also called Mendelian or monogenetic inheritance. This type of inheritance is caused by changes or mutations that occur in the DNA sequence of a single gene. There are more than 6,000 known single-gene disorders, which occur in about 1 out of every 200 births. These disorders are known as monogenetic disorders (disorders of a single gene).

Some examples of monogenetic disorders include:

• cystic fibrosis,
• sickle cell anemia,
• Marfan syndrome,
• Huntington's disease, and
• hemochromatosis.

Single-gene disorders are inherited in recognizable patterns: autosomal dominant, autosomal recessive, and X-linked.

Multifactorial genetic inheritance

•  Multifactorial inheritance, which is also called complex or polygenic inheritance. Multifactorial inheritance disorders are caused by a combination of environmental factors and mutations in multiple genes. For example, different genes that influence breast cancer susceptibility have been found on chromosomes 6, 11, 13, 14, 15, 17, and 22. Some common chronic diseases are multifactorial disorders.

Examples of multifactorial inheritance include:

• heart disease,
• high blood pressure,
• Alzheimer's disease,
• arthritis,
• diabetes,
• cancer, and
• obesity.

Multifactorial inheritance also is associated with heritable traits such as fingerprint patterns, height, eye color, and skin color.

Chromosome abnormalities

Chromosomes, distinct structures made up of DNA and protein, are located in the nucleus of each cell. Because chromosomes are the carriers of the genetic material, abnormalities in chromosome number or structure can result in disease. Abnormalities in chromosomes typically occur due to a problem with cell division.

For example, Down syndrome (sometimes referred to as "Down's syndrome") or trisomy 21 is a common disorder that occurs when a person has three copies of chromosome 21. There are many other chromosome abnormalities including:

• Turner syndrome (45,X0),
• Klinefelter syndrome (47, XXY), and
• Cri du chat syndrome, or the "cry of the cat" syndrome (46, XX or XY, 5p-).

Diseases may also occur because of chromosomal translocation in which portions of two chromosomes are exchanged.

Most common disorders

• P – Point mutation, or any insertion/deletion entirely inside one gene
• D – Deletion of a gene or genes
• C – Whole chromosome extra, missing, or both (see Chromosome abnormality)
• T – Trinucleotide repeat disorders: gene is extended in length

Disorder	Chromosome	Mutation
22q11.2 deletion syndrome	22q	D
Angelman syndrome	15	DCP
Canavan disease	17p
Charcot–Marie–Tooth disease
Color blindness	X	P
Cri du chat	5	D
Cystic fibrosis	7q	P
Down syndrome	21	C
Duchenne muscular dystrophy	Xp	D
Familial Hypercholesterolemia		P
Haemochromatosis	6	P
Haemophilia	X	P
Klinefelter syndrome	X	C
Neurofibromatosis	17q/22q/?
Phenylketonuria	12q	P
Polycystic kidney disease	16 (PKD1) or 4 (PKD2)	P
Prader–Willi syndrome	15	DCP
Sickle-cell disease	11p	P
Spinal muscular atrophy	5q	DP
Tay–Sachs disease	15	P
Turner syndrome	X	C

See you at class!!!