Basic questions

Below we will help you to understand more about genetics by way of 12 basic questions related to genetic diseases and genetic diagnosis:

What are genes?

Genes are the functional units of DNA. The human genome contains around 30,000 genes. As such, the genome can be considered to be an “instruction manual” that is used to ensure that all our cells function correctly. The DNA in each cell contains 3,000 million nucleotide bases (A, G, C, T, which represent the letters in which our genome is written) grouped into units known as chromosomes. Proteins, which are coded by genes, are the molecules responsible for performing all the tasks required by the different types of cells found in the human body. All our cells contains two complete copies of this genetic information, one copy from the person’s father and the other from the mother.

How do mutations in genes appear?

Genes normally contain some changes, which are not relevant from a medical viewpoint and which form the biological basis of the natural variation between different people. These changes can affect characteristics such as eye colour or hair colour. However, some changes in genes can affect the operation of a protein that performs functions which are of particular importance for cells. In such cases, this change in DNA triggers a disease, which can be passed on from one generation to the next. These pathological changes in DNA are known as mutations and are the underlying cause of genetic diseases.

What are genetic diseases?

Genetic diseases are those diseased caused by changes in the genetic material (DNA). Such changes to DNA are known as mutations. Some genetic disease are not hereditary. However, the majority of genetic diseases are hereditary, in other words they can be passed on from parents to their children. More than 6000 genetic diseases are known, and many of these diseases are currently being studied in order to identify the gene that causes them. Some of these studies have already borne fruit: we now know the genes that are responsible for more than 2000 genetic diseases, thus allowing us to perform an accurate genetic diagnosis.

How are genetic diseases triggered?

A person is healthy when all his or her cells perform their functions correctly. To this end, it is essential that all the proteins in each cell operate correctly. When a mutation occurs in gene, this changes the mode of action of one of these proteins, which can lead to a genetic disease. Some genetic diseases are passed on within families over many generations, and this can be detected when a doctor specialising in genetics studies the family history. However, other genetic diseases occur suddenly in families due to the appearance of a spontaneous mutation (de novo mutation).

Which diseases have a genetic cause?

The gene responsible for more than 2000 of the 6000 genetic diseases known has already been determined. As such, there are now more than 2000 types of different genetic tests that allow us to analyse the gene responsible for a large number of hereditary diseases in the laboratory. The list of available genetic tests is continually growing as a result of progress in genetic research. As such, it is essentially impossible to provide a full list of all hereditary diseases that we can detect in the laboratory. Such lists are only available for genetics experts in specialised databases. Some of the most well-known genetic diseases for which the corresponding genetic tests are already available include:

– cystic fibrosis – muscular dystrophy – haemophilia – Huntington’s disease – Marfan syndrome – neurofibromatosis – thalassemia – Charcot-Marie-Tooth disease – polycystic kidney disease – phenylketonuria – myotonic dystrophy – fragile X syndrome – retinitis pigmentosa – achondroplasia – hereditary ataxia – haemochromatosis – Prader-Willi syndrome – familial hypercholesterolaemia – breast and ovarian cancer – osteogenesis imperfecta

Is cancer a hereditary disease?

Most types of cancer are not hereditary. However, around 10% of cases occur as a result of inherited genetic factors that predispose a person with a specific mutation to suffer from a certain type of cancer. The identification of a mutation that predisposes for a specific type of cancer is of great help as your doctor can then recommend specific clinical routines to prevent it from appearing or for its early detection and treatment.

What is genetic diagnosis?

Genetic diagnosis is a highly complex tests that is performed by a laboratory specialising in analysis of the genome. Such studies are used to identify the genetic cause (mutation) of a specific disease in a patient, thus preventing it from being passed on to his or her children. In some cases, such mutations can be so large that they can be seen by observing the chromosomes under a microscope. This type of analysis is known as karyotyping, or a cytogenetic study. However, mutations are normally so small that they affect only one chemical base in the DNA (one letter in the genome). As such, highly sophisticated DNA analysis techniques must be used to detect these small mutations. These techniques, which are much more complex, are known as molecular studies and are normally performed by sequencing a small part of the patient’s genome.

How is a genetic analysis performed?

To perform a genetic analysis it is necessary to study the genetic material found in our cells. The type of sample needed to obtain this genetic material is normally a small quantity of blood. To perform a chromosomal study (or karyotype), the cells must be cultured and processed in order to be able to observe the chromosomes under a microscope. To analyse a specific region of DNA, this DNA must be extracted from the cells and specifically analyse the region of the genome of interest. The most definitive analytical method for genetic diagnosis is DNA sequencing, which is the same technique used to decipher the human genome. This technique is considered to be the strictest quality standard for genetic diagnosis as it allows the genetic information for a person to be read down to the chemical bases from which DNA is formed (A, G, C, T, the alphabet of the genome).

Who may be a candidate for a genetic diagnosis?

The appearance of diseases that may have a genetic component is occasionally observed in some families. These cases are often worrying, especially when we decide that we want to have children. The main reasons why you may be recommended to attend a specialised genetic consultation are as follows: · Presence of a hereditary disease in the family or the suspicion that a disease may be hereditary. · Presence of diseases with a genetic predisposition, such as cancer, neurodegenerative disease or cardiovascular disease, in various family members. · Repeated miscarriages. · Infertility. · Previous cases of newborns with congenital diseases, dysmorphias or syndromic forms in the family. · A risk evaluation during family planning, especially in older women.

How can I decide whether to undergo a genetic analysis?

If you consider that you might be at high risk if suffering from (or passing on) a hereditary disease, talk to your doctor. Your doctor will help you to take the best decision regarding the advisability of undergoing this type of analysis. We recommend that you do not take such an important decision alone. Your doctor will evaluate your family history. To do this, he/she will ask questions about your health and the health of your close relatives. This information will help your doctor decide what risks you (or your family) may have. Your doctor will also explain the results of your genetic analysis to you once they are available from the laboratory.

How and where can I request a genetic analysis?

A genetic analysis must always be prescribed by a doctor and must be performed by a specialised and duly accredited laboratory. There is an international consensus advising against members of the public undergoing a genetic diagnosis directly without talking with their doctor first. As such, we must stress the importance of talking with your doctor before undergoing a genetic test so that he/she can inform you of the benefits of this analysis and the results that you may obtain. The Institute for Genomic Medicine does not, therefore, offer genetic analyses directly to the general public. If you are a medical professional, our Reference Laboratory is available to you for analysis of any of the known genetic diseases with an underlying molecular basis. If you have any questions about out catalogue of genetic analyses, you can call our direct helpline for medical professionals, where you an talk to one of our medical genetics experts (tel. +34 96 321 23 40). If you are a patient or a member of public and need a medical genetics consultation, you can call us at the Institute for Genomic Medicine and we will help you to find a doctor with experience in treating genetics-related problems.

Where can I find more information concerning hereditary diseases and genetic diagnosis?

If you are looking for more information concerning genetic diseases, rare diseases or the different types of genetic diagnosis currently available, we recommend that you visit the genetic diseases web page published by the US National Library of Medicine: www.nlm.nih.gov/medlineplus/spanish/geneticdisorders.html If you are looking for more information about hereditary cancer, we recommend that you visit the web page about cancer and associated genetic tests published by the US National Cancer Institute: www.cancer.gov/cancertopics/understandingcancer/espanol/las-pruebas-geneticas If you are a medical professional and you wish to receive further information concerning genetic diseases or the best way of introducing genetics into your daily practice, we can provide you with access to a large collection of scientific and explanatory materials. Please do not hesitate to contact us to obtain an y further information you may require.