Types of Genetic Diseases
There are several types of genetic disorders. The way in which the disorder is inherited can help determine the risks it will have on a pregnancy and the risk of recurrence it will recur in future children. Risks for having a baby with a birth defect from a genetic abnormality may be increased when:The parents have another child with a genetic disorder.
There is a family history of a genetic disorder.
One parent has a chromosomal abnormality.
The fetus has abnormalities seen on ultrasound.
The types of genetic disease:
Chromosomal abnormalities
Single gene defects
Multifactorial problems
Teratogenic problems
Chromosomal abnormalities:
Chromosomal abnormalities in the baby may be inherited from the parent or may occur with no family history. It is include:
Numerical disorders:
Aneuploidy. Abnormal number, includes:Autosomes
Trisomy 21 (47 chromosomes)
Down syndrome.
Klinefelter syndrome 47, XXY male.
Trisomy 18
Edward's syndrome.
Trisomy 13.
patau's syndrome.
Trisomy 8
Warkany syndrome 2.
Trisomy X syndrome.
Note : all other autosomal trisomy are lethal.
Sex chromosomes
Monosomy 21 (45 chromosomes)
Turner's syndrome= missing of X in female).
Note : all other autosomal Monosomy are lethal.
Polyploidy: Multiple of the haploid (Diploid).
Tetraploidy (4n).
Triploidy (3n).
Structural disorders:
Balanced
Inversion (inv):When a chromosome breaks and the piece of the chromosome turns upside down and reattaches itself. Inversions may or may not cause birth defects depending on their exact structure.
Translocation (t): A rearrangement of a chromosome segment from one location to another, either within the same chromosome or to another.
Robersonian translocation (rob): A balanced translocation in which one chromosome joins the end of another.
Non-balanced
Deletion (del): Part of a chromosome is missing, or part of the DNA code is missing.
Duplication (dup): is the presence of double examples of the same chromosomes.
Isochromosome (I, iso): abnormal chromosomes formed of two short shoulders or of two long shoulders.
Ring chromosome (r): appeared after chromosomal tearing in two points of different shoulders, followed by terminal segment (acentric) loss and centric segment’s ends joining in a ring structure.
Single gene disorders:
Single gene disorders are caused by DNA changes in one particular gene, and often have predictable inheritance patterns.
Dominant. An abnormality occurs when only one of the genes from one parent is abnormal. If the parent has the disorder, the baby has a 50 percent chance of inheriting it. It is include the following:
Achondroplasia. Imperfect bone development causing dwarfism.
Marfan syndrome. A connective tissue disorder causing long limbs and heart defects.
Recessive. An abnormality only occurs when both parents have abnormal genes. If both parents are carriers, a baby has a 25 percent chance of having the disorder. Examples include the following:
Cystic fibrosis. A disorder of the glands causing excess mucus in the lungs and problems with pancreas function and food absorption.
Sickle cell disease. A condition causing abnormal red blood cells.
Tay-Sachs disease. An inherited autosomal recessive condition that causes a progressive degeneration of the central nervous system, which is fatal (usually by age 5).
X-linked. The disorder is determined by genes on the X chromosome. Males are mainly affected and have the disorder. Daughters of men with the disorder are carriers of the trait and have a one in two chance of passing it to their children. Sons of women who are carriers each have a one in two chance of having the disorder. Examples include the following:
Duchenne muscular dystrophy. A disease of muscle wasting.
Hemophilia. A bleeding disorder caused by low levels, or absence of, a blood protein that is essential for clotting.
Multifactorial problems:
Some birth defects do not follow a single gene or chromosomal abnormality pattern. They may be due to several problems, or a combined effect of genes and the environment. It is difficult to predict inheritance of abnormalities caused by multiple factors. Examples include diabetes , heart defects, cleft lip or cleft palate, and neural tube defects (defects in the spine or brain).
Teratogenic problems:
Certain substances are known to cause abnormalities in babies. Many birth defects occur when the fetus is exposed to teratogens (substances that cause abnormalities) during the first trimester of pregnancy when organs are forming. Some known teratogens include the following:
Certain medications (always consult your doctor before taking any medications during pregnancy) eg captopril, enalapril, tetracycline .
Alcohol.
High level of radiation exposure.
Lead.
Certain infections (such as Rubella).