Hereditary diseases
Hereditary diseases are genetic diseases. So they are passed on from parents to children with the genetic material. This can happen even if the parents show no signs of illness themselves. Hereditary diseases are triggered by defects or irregularities within the genetic make-up. One gene or even several genes can be defective at the same time. Find out what hereditary diseases there are, how they are diagnosed and what approaches modern medicine has developed to treat them.
Which hereditary diseases are there?
Genetically determined clinical pictures are very diverse. Congenital genetic defects can lead to dysregulated tissue growth, disrupt or block certain metabolic reactions and even let certain cell types perish.
Hereditary diseases thus range from metabolic diseases (example: phenylketonuria) to developmental disorders (example: trisomy 21) to progressive muscle weakness diseases (example: spinal muscular atrophy).
How is the genome structured?
The blueprint for the human body and all of its functions are stored in the genome. The individual pieces of information are stored on so-called genes - organized in 46 chromosomes.
Each chromosome is in pairs (duplicates). The sex chromosome pair (gonosomes) is an exception: in women it consists of a double X chromosome, in men it consists of a combination of the X and Y chromosomes.
In contrast to tumor diseases, the genetic predispositions for hereditary diseases exist from birth. Parents pass on certain genetic traits via the germ cells from one generation to the next.
Hereditary diseases from A to Z
A.- Albinism
- Alpha-1 antitrypsin deficiency
- Amyloidosis
- Angelman Syndrome
- Chorea huntington
- Down syndrom
- Factor V Leiden
- Color blindness
- hemophilia
- Kallmann syndrome
- Klinefelter Syndrome
- Marfan's Syndrome
- Hirschsprung's disease
- Cystic fibrosis
- Phenylketonuria
- Proteus Syndrome
- Retinitis pigmentosa
- Sickle cell anemia
- Spinal muscular atrophy
- Thalassemia
- Treacher Collins Syndrome
- Trisomy 13
- Trisomy 18
- Turner Syndrome
How are hereditary diseases classified?
Doctors divide hereditary diseases into the following groups:
Chromosomal diseases: This type of genetic disease is associated with an altered structure or an altered number of chromosomes. In many cases this leads to serious developmental disorders.
Monogenic diseases: diseases that are caused by a narrow, specific gene modification. In most cases, the body then does not produce an important protein molecule such as a metabolic enzyme, in a modified form or in insufficient quantities.
Polygenic disorders: They are characterized by a large number of (minor) changes in the genetic make-up. This means that only the complex interplay of several genetic variations (polymorphisms) leads to a hereditary disease. In many cases, environmental influences and living conditions trigger genetic diseases of this type.
Chromosomal diseases
In the case of a chromosomal disease, there are deviations in the natural order of the chromosomes. Reasons for this can include the incorrect formation of egg and sperm cells - or their incorrect fusion during fertilization. In the narrower sense, therefore, they do not count among the hereditary diseases as such. External influences such as high-energy radiation or certain chemicals can also damage germ cells (egg cell, sperm).
If the number of chromosomes deviates from the natural distribution, in many cases serious consequences arise - such as malformations and developmental disorders in the child. Chromosomes can be present in about three places - one then speaks of so-called trisomies.
In trisomy 21 (Down syndrome), for example, chromosome 21 is affected. Children with this chromosomal maldistribution are usually severely stunted in their development.
Another representative of this group is trisomy 18 (Edwards syndrome) in which chromosome 18 is present in triplicate. In trisomy 13 (Patau syndrome), chromosome 13 is correspondingly overrepresented. Both forms show an increased child mortality.
Another chromosomal disease is Klinefelter syndrome, which occurs exclusively in males. Instead of a regular XY sex chromosome, there is an additional X chromosome - the result is a chromosomal XXY scheme.
Among other things, this has an effect on the formation of the male sex hormone testosterone. Therefore, the Klinefelter syndrome often only becomes noticeable during puberty. In many cases, those affected are tall. Affected people are also mostly sterile because their testicles are underdeveloped.
Turner syndrome is a chromosomal disease that only occurs in women. Here, too, the cause is a maldistribution in the sex chromosome pair. Affected women only have a single X chromosome. The symptoms can be varied, but do not always occur fully in all patients. Often those affected are short.
Monogenic diseases
A monogenic disease - also called a monogenic disease - can be traced back to a “defined” gene defect within a certain gene sequence. This means that a certain gene that codes for an important protein molecule is not (fully) functional.
As a result of this faulty blueprint, the body then usually produces non-functional protein molecules. This can have direct consequences for the metabolism, cellular control mechanisms or for organ functions. A lack of certain protein molecules can also cause body cells to die or certain physical stages of development can no longer be reached. Monogenic diseases often appear in childhood and usually follow Mendelian inheritance rules.
Autosomal recessive inheritance: The loss of function only becomes apparent when both parents, who carry the same defective genetic makeup and have passed it on to their child. If both partners are carriers, then the child has a 25% risk of developing the disease. Examples of such hereditary diseases that follow an autosomal recessive inheritance are cystic fibrosis, phenylketonuria, albinism, galactosemia, sickle cell anemia and certain forms of spinal muscular atrophy.
Autosomal dominant inheritance: According to the Mendelian inheritance rules, some diseases are also inherited dominantly. This means that an altered gene cannot be compensated for by a functional copy on a neighboring allele or chromosome.A single copy of the genetic error from just one parent is then sufficient for it to prevail against the healthy gene of the other parent.
Such a hereditary disease usually occurs in every generation. The respective disease can break out in childhood or in adulthood. Examples include brachydactyly (people with shortened fingers), factor V disease (blood clotting disorder), Marfan's syndrome (connective tissue disease), Huntington's disease (motor brain disease) and certain forms of myotonic dystrophy ( Muscle disease) or retinitis pigmentosa (disease of the retina of the eye).
X-linked inheritance: The so-called X-linked inheritance is a special case. There is a genetic defect on an X-chromosome of the sex-specific gonosomes.
In the case of an X-linked recessive gene defect, men usually get the disease, as they “only” have one X sex chromosome. In women, however, the remaining second X chromosome compensates for the faulty gene with its intact copy.
Examples of typical diseases that follow an X-linked recessive inheritance are "hemophilia" (factor VIII disease or hemophilia), muscular dystrophy type Duchenne (disease of the muscles), mucopolysaccharidosis type II (Hunter's disease, a metabolic disease) or the red-green color sense disorder (color blindness).
In contrast, X-linked dominant inheritance patterns rarely occur. Here, too, there is a genetic defect on the gender-specific X chromosome. An example of an X-linked dominant disease is hypophosphatemic rickets (vitamin D-resistant rickets, a disorder of bone metabolism).
Polygenic diseases
A wide range of different forms of disease is hidden under polygenetic or polygenic diseases. These variations in the genome are also called “Single Nucleotide Polymorphism” (SNP).
Viewed in isolation, individual SNPs usually do not lead to an increased risk of disease - but the interaction of many different, complementary genetic factors still influences the state of health.
Examples of diseases in this group are widespread diseases such as allergies, type II diabetes, cardiovascular diseases or cleft lip and palate and pyloric stenosis (narrowing of the stomach outlet). What they all have in common is that the disease is usually not influenced by genetic predisposition alone, but also by external factors - for example, existing living conditions, environmental influences or the general lifestyle.
Hereditary Diseases - Diagnosis
Advances in modern medicine make it possible to identify risks for hereditary diseases in many cases at an early stage. This is possible, for example, through what is known as a human genetic examination.
Many specialized clinics offer individual advice services that serve as the first point of contact for those seeking advice. They help and advise on:
- Clarification of common family diseases
- Risk assessment when trying to have children
- molecular diagnostics of hereditary diseases
- comprehensive explanation of possible therapeutic approaches
- possible conditions of admission and participation in clinical studies
- Education about the severity, course and prognosis of a hereditary disease
- Mediation of other specialized contact points and patient representatives
For whom is human genetic counseling suitable?
Genetic counseling is suitable for anyone who is concerned about whether a family member or themselves have a hereditary disease that can be passed on to their offspring. It takes place with specialists in human genetics.
For example, if the pediatrician diagnoses a developmental delay in your child, he will clarify a hereditary cause. Such advice can also be useful in family planning, especially if certain illnesses occurred more often in the family or abnormalities - for example on ultrasound - come to light during pregnancy.
What human genetic studies are there?
The focus of individual genetic counseling is on examination procedures to identify the risk factors at an early stage. In this way, doctors can initiate suitable therapy - if available - at an early stage and ensure the best possible care.
During pregnancy, for example, your doctor can obtain important conclusions about the development of the unborn child through so-called non-invasive prenatal tests. It is a "simple" blood sample taken from the vein of the expectant mother.
On the one hand, doctors determine whether certain metabolic markers provide information about the state of health of the unborn child, on the other hand, they search specifically for fragments of the child's DNA.
Since certain fetal DNA fragments (cell free DNA or cfDNA) are already circulating in the mother-to-be's blood, it is possible for doctors to search for genetic abnormalities in the unborn child (PrenaTest and Panorama-Test, Harmony-Test).
A direct examination of the child is also possible as part of routine newborn screening (early detection) on the second or third day of life after birth. To do this, doctors take a few drops of blood from the heel of the newborn and clarify possible congenital metabolic disorders, hormonal disorders or other hereditary diseases.
Can hereditary diseases be cured?
Most hereditary diseases are incurable. However, this answer cannot be applied across the board to all hereditary diseases. The underlying triggers and manifestations of the corresponding clinical pictures, which mostly count among the rare diseases, are too diverse and complex.
Hopeful approaches have recently become available for one form of hereditary retinal dystrophy (RPE65 mutation) or hereditary spinal muscular atrophy. For the first time, doctors have the opportunity to help those affected with gene therapy approaches.
A timely molecular diagnostic clarification is particularly important here, since the success of the treatment benefits from an early diagnosis and a corresponding early start of therapy.
Nevertheless, there are treatment options for many hereditary diseases. For example, missing proteins can be supplied artificially, as is the case with hemophilia. Or certain food components that cannot be processed are avoided through a special diet (example: phenylketonuria). For many hereditary diseases there are medical centers and self-help groups that offer advice or special therapies.
