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Genetic Testing of Diseases

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Causes for genetic disorders

Genetic disorders are caused by changes in the structure or number of the chromosomes or in the DNA


Genetic problems arise due to different reasons:

DNA and GENES: The DNA, is a unique, spiral- shaped molecule found in all living cells. It is called the ‘blue print of life’ and controls the existence of most creatures on earth. A specific segment of the DNA that codes for specific body proteins is called the gene. The DNA and the genes are compactly arranged on the chromosomes.

Genes encodes for proteins some of which, such as enzymes, carry out significant life functions. There are no genes that actually cause a disease. Changes in the genes called mutations, alter the structure function of the gene products which gives rise to diseases. A mutation in a single gene may result in a serious disorder like cystic fibrosis, achondroplasia or sickle cell anemia.

Researchers have identified several oncogenes or cancer- causing genes in the humans. A mutation in one of these oncogenes results in cancer in an individual. A classical example is a mutation in the oncogenes BRCA that increases the susceptibility of breast cancer by 85% and ovarian malignancy by 50% in women.

Sometimes a mutation in the genes on the sex chromosomes results in a disorder. Mutations in certain X-linked genes result in specific diseases like Hemophilia, Muscular dystrophy and Fragile X syndrome. The most common type of ectodermal dysplasia, hypohidrotic ectodermal dysplasia (HED) is caused by a mutation in the ectodysplasin-A (EDA) gene.  Women are often only carriers of these X-linked disorders as they have two copies of the X chromosomes. Men, on the other hand, are affected as they have only a single X chromosome. Deletion of certain Y-linked genes, like the SRY, result in infertility in men.

Chromosomes: Humans have 46 chromosomes, arranged as 23 pairs, in each cell. Each chromosome of a pair is inherited from each of the parent.

An error may occur in the cell division either before or after embryo formation. The embryo will then have decreased or increased number of chromosomes. For eg, a Down syndrome individual has three copies of chromosome 21 when there should only be two. This condition is called a trisomy. Edward’s syndrome (trisomy 18) and Patau’s syndrome (trisomy 13) are the other examples. Down syndrome is the most common of all the trisomy and has a fairly good life expectancy. The rate of survival for the other trisomies is, rather poor. When a single copy of a chromosome is present it is known as monosomy. Survival is not known as it results in abortions or stillbirth.

Some genetic conditions also occur as a result of the sex chromosomes being more or less in number. A male has a X and a Y chromosome while the female has two XX. Sometimes a female has only a single X chromosome. This results in a Turner’s syndrome.Sometimes a male can have extra numbers of X chromosome causing Klinefelter syndrome in the affected individuals.

In certain cases the number of chromosomes may be intact, but a part of the chromosome will be missing. This is called a deletion, which will result in the loss of a single gene or a few genes. Classical disorders caused by a deletion are the Cri-du-chat or the ‘cat-cry’ syndrome, Di George syndrome and William syndrome. Translocations occur when parts of the chromosomes get transferred from one chromosome to the other. Inversions, on the other hand result when parts of the chromosomes get deleted and get inverted to get re-inserted again. Translocations and Inversions do not cause malformations. They may cause later life complications like infertility or miscarriages.


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One of my relative's son has low biotinidise enzyme. He was born 2 weeks ago in USA and is using biotin 5MG tablets now. They are in USA and want to come to Chennai - in 3 months from now [2-June-2015]. They were told that a blood sample needs to be tested for biotin every 6 months to adjust the dosage of Biotin prescribed for the baby. Is Biotin tablets for infants available in Chennai? Is there medical centers/labs/doctors at Chennai who treats such biotin related gene disorder? Any early response is greatly appreciated. Thanks !
Saravana_Solaisamy Tuesday, June 2, 2015
Dear Doctor, My daughter is suffering from CAH and she need a genital corrective surgery. She is under AIIMS treatment. I do not know if where CAH is being treated. Due to a long waiting time I wish to have an alternate opinion. Please suggest me. Thanks a lot.
mjav123 Monday, September 8, 2014
Hello Doctor, can you please suggest the best place in India for genetic counseling. My daughter who is now 5 1/5 years old had long segment hirschsprungs diseases at birth which was treated with pull through surgery. Both me and my husband are not aware of any family history of hirschsprungs in our family. Now I am planning for another kid but before that want to be sure of the underlying reason for my daughter's condition and the chances of recurrence in future pregnancies. Any advice on this will be very much appreciated. Thank you!
Noorian Wednesday, June 25, 2014
The best genetic counselor in India by popular consensus is Dr.Ashok Prasad who is a professor also holding a genetic counseling masters from Brandeis University. He works only on a charitable basis in Gorakhpur but am sure could be persuaded to advise you
suparnadas Sunday, July 27, 2014
Hello doctor, we had a child who was effected by spinal muscullar attrophy[type one]. Now we are planning for our next baby. doctor told us to go for CVS testing. but I want to know whether there is any other ideal option for us.Pleas give me suggestions. Subhajit bhowmick
tulika12345 Wednesday, June 25, 2014
helllo doctor,my wife is a pregnant our doctor is prefre to amniocentesis so plz tell me where i do in delhi,india and how much it cost
roopagupta Wednesday, May 21, 2014
Hello Doctor, My daughter has wardenberg syndrome due to that she has hearing loss. I am planning for cochlear implant. Please tell me what is the other side effect of this syndrome
Ruchi_1985 Wednesday, March 12, 2014
Hello doctor. My son is having primary microcephaly. He is going to regular school and takes help of special educators. He had delay in speech and we took him to a speech therepist for that. He will turn 5years old in march. We now want to plan for our second child but we are worried that our second should not suffer from any such thing. Please suggest what all tests we shall get done before conceiving and from where. We live in delhi. Plz suggest some good doctor also.
gk.09 Wednesday, February 12, 2014
Dear gk.09,

Microcephaly could either occur as an isolated feature or at most times, as a part of a syndrome [along with other clinical features]. The causative genes are several hence, you a panel of genes will need to tested to find out the specific genetic cause in your son. Only then, can you opt for prenatal diagnosis where in it is possible at 3 to 4 months of pregnancy to test if your fetus had also inherited the same genetic condition.

Dr. Risha Nahar
Genetic Consultant

Guest Thursday, March 5, 2015
hi,in india which hospital have done genetic testing for frontotemporal dementia ?please reply soon.
devi.u Tuesday, July 2, 2013
Hi! Do Come to Sri Ramachandra Medical College and Hospital at Porur, Chennai. Get Well Soon..!!
avinash1005 Monday, December 30, 2013
hello doctor, how can i contact cousin is suffering from muscular dystrophy. and doctors have already told that he wont live more than 20 yrs. only female baby can survive out of it. thus my aunty has conceived again.we just wanted to know whether the baby inside her womb is out of this disorder or not.
matilda.loisel Saturday, March 30, 2013
Hi! Its really unfortunate that your cousin is suffering from Muscular dystrophy. A female baby from your aunt could survive, but the odds of her being the carrier of Muscular dystrophy is high. She may be healthy, but she can pass-on the disease to her son. Hence its recommended to get a genetic testing of the developing fetus and take gene therapy to prevent and eradicate the disease from occurring in future generations...
avinash1005 Wednesday, December 18, 2013
Respected Doctor,
My brother was suffering eye sight by birth and which we know at his 7-8 yrs. then with the growing yrs. his eye sight also get on increasing.
then as last we consulted to dr. vivek sahay of MARTI PRERNA EYE HOSPITAL RANCHI in 2008 and this time his power was -18 and dr. operate ICL to him at JAN 2009 but some problems stay as usual
so in jan 2013 we went to kolkatta at vasan eye care to consulted dr. sen he said that he is suff. RHINITIS PROGNATHOUS which will happen to his next generation and can never be cured and we want his married life
so i want your suggestion sir . please help and suggest me what can we do?

sweety23 Tuesday, January 29, 2013
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