Prader Willi syndrome is the most frequent form of obesity caused by one faulty gene. One of its typical features is unsatiable appetite, gluttony, which is often considered a synomym of the syndrome, even though it is only one of the symptoms.
Symptoms: low birth weight, very weak muscles, slow weight gain, gluttony.
The syndrome affects one child in 10-25 thousand, it appears sporadically.

Based on regional data, if affects one child in 18 thousand in Hungary. 

The Swedish have conducted a more thorough survey, where they focused on children, and found one affected in 12-13 throusand. The syndrome affects either sex with equal probability, and is typically not hereditary: its probability is less than 1 per cent.
The syndrome is caused by genes. Basically it means it is not inherited through the classic dominant or recessive patterns. That is why cases are not cumulated in families.

The symptoms are caused by a disorder of the central nervous system, which creates – among other things – the unsatiable appetite, i.e. when the feeling of hunger is not switched off by the central nervous system after meals, as it for healthy kids. Kids affected by Prader Willi syndrome can never eat enough for that. That is why they become very overweight.
The syndrome can be confirmed by genetic testing, which is conducted based upon clinical reason to suspect Prader Willi syndrome based on the symptoms. The test is done on the DNA of cells taken from the patient’s blood.
Those affected are born with low weight, and during the first year of the lives, the leading symptom is extreme muscle weakness (hypotonia), while they slowly gain weight. The reason for the latter is muscle wekness, as the muscles around their mouths are so weak they get tired of eating. It is hard to breast-feed them, too, actually impossible for many of them, thus they need to be fed through gastroenteric feeding tubes or from nursing bottles. That is one of the most typical differences between simple excessive weight gain and Prader Willi syndrome. Children who gain two kilograms by the age of one month are definitely not affected by Prader Willi syndrome. 

Kids affected by Prader Willi syndrome start showing signs of gluttony later, at the age of 1-6 years, when their appetite becomes unsatiable. That is typically the time when the syndrome can first be diagnosed.

The mental abilities of the patients vary on a wide range. Some graduate from high school, but others are seriously mentally handicapped. They may display behavioral problems, tantrums.
Prader Willi syndrome is not curable, but can be managed by appropriate lifestyle and development techniques. There are diets and recommendations (like cutting off access to food altogether) that can help, but due to the fact that the part of the nervous system that regulates appetite does not work properly in these kids, it is very difficult to adhere to such regimens.

In order to manage the behavioral issues, psychological counseling may also be necessary. It is important to note that in case of these patients, it is not recommended to apply medication that modifies their behavior or appetite. In serious cases, only haloperidol or fluoxetin derivatives may prove effective. Potentially growth hormone (GH) therapy may increase body heights, improve muscle strength, thus supporting development and regular physical exercise, better body composition, thus helping to avoid further weight gain. What is important to add is that growth hormone therapy does not promote development of intelligence, as its effects on mental capabilities is not proven.

If other conditions appear affecting endocrinology or metabolism (like insulin resistance, male sex hormone deficiency, hypothyroidism), hormone therapy may be required. Due to their weak muscles and breathing, patients may experience more frequent respiratory infections, requiring antibacterial treatment.
The syndrome cannot be cured, but can be managed. Life expectancy may be gravely lowered by such complications, and then we may lose the patients at their late twenties or early thirties.

The outlook for Prader Willi patients may greatly vary subject to genetic background and development potential. The risk of sudden death is quite high both in childhood and adulthood (annually about 3%), primarily due to cardiovascular and pulmonary causes associated with obesity. If overeating and obesity is avoided, life expectancy is in the normal range. 

The behavioral issues and tantrums may improve in young adulthood. Those affected can live in communities under controlled circumstances.

Asperger syndrome is a “milder” type of autism that does not manifest in any external signs, intelligence or learning ability. To the contrary, many people with Asperger are extremely smart, and possess special skills and outstanding talent.
However, they have major problems in the context of interpersonal relations and communication. It is quite difficult to recognize mild Asperger syndrome: experts say that about half of the people living with Asperger are never diagnosed.
Typical features of Asperger syndrome are a lack of empathy, difficulties in establishing interpersonal relationships and a lack of joy triggered by social interactions. One first symptom parents might recognize is a lack of eye contact (or that of other non-verbal communication means, gestures, facial expressions). Kids with Asperger have difficulties with sharing objects with others or participating at games.
However, it does not mean that they are totally isolated from others. They very frequently try to approach others, but do that their own specific ways, and are incapable of interpreting others’ non-verbal signs and emotions.
Another typical feature of Asperger syndrome is an abnormal dependence upon certain patterns, behavior and routines, as well as an extreme focus of attention of a specific well-defined area of interest. People with Asperger can gather an incredible amount of information about something without showing any interest for (or ability to understand) the larger context of the same topic.
Repetitive patterns may appear in their movements, too, in the form of a typical series of gestures for example. These gestures often involve the whole body, and unlike tics, these series of gestures are voluntary.
In terms of speech development, children with Asperger syndrome do not have any serious issues with learning to speak, but the way they express themselves may often be unusual, and they may have difficulties with understanding humor, ambiguity or irony. Their manner of speech is often rigid, pedant and formal. They may apply unusual intonation and rhythm, as well as it may be unusual how loud they speak. (For example, they may speak very fast or loud even when not required.) It is frequently observed that people with Asperger automatically repeat what others say. At the same time, children with Asperger syndrome have a very extensive and sophisticated vocabulary.
Asperger syndrome may involve deviant perception. Those affected are often very observant, have very good memory, but may be sensitive to sounds, light or smells.

Affected children are often clumsy, i.e. some of their motoric skills are slow to develop. They might have a hard time learning how to ride the bicycle, jump around or write in readable letters. They may have issues with spatial perception (especially with potitioning themselves spatially) or keeping their balance.

Angelman syndrome (AS) is a hereditary neurological condition involving mental handicap. It is caused by a defective chromosome 15. Some of the genes on chromosome 15 affect the development of the brain, including primarily development of verbal and motoric skills. It is a slowdown of that development that is typical of children suffering from the syndrome. Nevertheless, despite their mental handicap, these kids are visibly happy. They smile and laugh a lot.
 Infants born with Angelman syndrome do not seem unhealthy at birth. The shape of their faces may be peculiar, but not always obviously to such an extent as in case of other hereditary conditions. They may typically have broad, smiling faces (happy face), protruding chins and thin upper lips. They often push out their tongue between their lips. Their heads are sometimes smaller than the average, and the skulls in the back are flatter than usual. Problems might not be recognized at birth, only later, at the ages of 1-2 years. Then, deficiency may appear in speech development and motoric skills. These babies babble a lot less than usual in their age, and are very slow to learn the first words. It may take for long months to utter the simplest words. Their vocabularies are very-very limited, which does not change later either – in more serious cases, the patient does not use more than 10-20 words. They often communicate with tactile, non-verbal signs. They push away undesired objects or pull their parents towards things they need.  Their posture is rigid, and often unusual movements are perceived.
In later years, additional symptoms become more apparent, including a tendency for spasms in the form of epilepsy-like attacks and hyperactivity, which make it extremely difficult for the kids to remain focused. Motoric hyperactivity is the most apparent. It may seem that the baby never rests. Later sleeping disorders may also appear, which require medication in serious cases. Due to the attention disorder, the involuntary movements, the mental handicap and the communication issues, Angelman syndrome is often misdiagnosed as autism, though autists strive to avoid human interaction, and do not seem to be happy and curious, like people with Angelman syndrome do, but rather lack any facial expression.
Most patients do not become fully independent adults. Most of them learn to use forks and knives, but face difficulties with putting on clothes that have buttons or zippers. Despite all that, they are very happy, kind people, who seek and love company. Though personal interactions are difficult because of the speech difficulties, they always find a way to make themselves understood. Many of them learn sign language, though sometimes use modified forms due to the limited motoric skills. They also frequently use different means to support their communication.

Diagnosis is possible based on clinical symptoms and DNA testing. The latter also offer an opportunity to determine inheritance patterns, which is important to determine repetition, as well as prognosis within certain boundaries. Even though life expectancy, without regard to inheritance pattern, is high, and they live almost as long as healthy people, some of their skills can be developed more or less subject to inheritance mechanisms (like gene-deletion, uniparental dysomy etc.). The syndrome is unfortunately still uncurable, only the symptoms can be managed. In case of serious sleeping disorders, regular epileptic seizures, medication is required, but along with that, primarily behavioral therapy and speech development should be in the focus.

This might be the most widely known genetic disorder of all. All of us know of some people living with Down syndrome.

Down syndrome is the most frequent of congenital multiple disorders compatible with life, the leading symptoms of which are anatomical defects affecting several organs and mental handicap of varying degree.

Geneticaly we differentiate three basic types: in addition to types caused by extra copies of chromosome 21 in every cell (trisomy 21), and ones caused by the presence of only extra parts of chromosome 21 (translocation), there are ones caused by so-called mosaicism (2.4%), where mutation (changes in gene pool) occur in course of the multiplication of cells, thus causing the presence of healthy and mutant cells in the same organization.
Symptoms: mental handicap, low height, obesity, underdeveloped testicles, decreased muscle tone, open mouth, protruding tongue, excessive joint flexibility, round head, mild small headedness, slanted eyes, small penis.
In Hungary, Down syndrome occurs in about 1 case out of 1000 pregnancies (1.17 per mil). Its rate of occurance has not been impacted by even the gravest global environmental catastrophies (eg. the nuclear disasters of Hiroshima, Nagasaki or Chernobil). However, the age of the mother is clearly a factor. The occurrence rate among young mothers is approximately 1/1500 pregnancies, while at the age of 40, it reaches 1/50 (2%), which rate increases by 1% by each additional year. At the age of 46, for example, risk of occurrence is 6%.
For us to understand the genetic background of Down syndrome, we need to recall the basics of chromosomes. Our cells contain 23 pairs of chromosomes, i.e. 46 chromosomes. We inherit 23 chromosomes from each parent. That is possible in a way that when sexual reproductive cells evolve a cell division process called meiosis takes place that cuts the number of chromosomes in half, so reproductive cells do not contain chromosome pairs. When ova and sperm cells fuse, they create a cell that again contains chromosome pairs: so half of genetic information is inherited from the father, the other half from the mother. In course of the division of that, the genetic pool does not change.

An overwhelming majority of Down syndrome cases (94%) are of the trisomy type, caused by a so-called non-disjuctio occurring in course of the meiosis of the sexual reproductive cells of one of the parents, i.e. when chromose pair 21 does not split, thus creating a cell that has two chromosome 21s and another one with none. out of the two defective sexual reproductive cells, the one without chromosome 21 cannot survive, thus it does not lead to a defective offspring. However, when a reproductive cell with an extra chromose 21 fuses with its counterpart, they constitute a cell containing 47 chromosomes, including three 21s, thus every cell of the child will contain 47 chromosomes.

Causes are unknown. The current hypothesis is that egg cells get old, while sperm always regenerate. Egg cells are assumed to be always the same age as the mother, including the earliest embryonic stages of the mother’s life. Even 3-month-old embrios contain all the egg cells (app. 1 million), which can be the basis for later reproduction. Later, the number of egg cells decreases, at birth, there are “only” about 300000. That is how egg cells may get old by the age of 40.

The other type is the so-called translocation, which occurs in 3-4% of all cases. This structural disorder is caused by a part of a chromosome 21 getting split from the chromosome (deletion), then attaches to another chromosome (translocation). As the chromosome set of every bodily cell is complete, this disorder does not cause any symptoms for the parent. The parent carries a so-called balanced translocation, but can hand down to the child a translocation form that causes Down syndrome. The risk of the offspring depends then on the type of structural damage and whther it is the mother or the father that carries it. Translocation may occur as a newly formed mutation, but can also be inherited from a parent carrying a balanced chromosome disorder.
The symptoms of Down syndrome are so typical that diagnosis can be established based on clinical signs only.

However, it is important that trisomy and translocation types cannot be differentiated based on clinical symptoms.

The most general symptoms include overall weak muscle tone, frequently open mouth, protruding tongue, very loose joints, low body height, clumsy movements.
Adults are often obese. The head is round, the back of the neck is flat, and the head is slightly small. The neck is shorter than usual. Skull bones are thinner, fonticuli are slow to close. The nose is small, The nose bridge is small. Eyes are slanted ("mongoloid eye slant”), there are small skinfolds on the inner corners of the eyes (epicanthus). Dots on the iris ("Brushfield spots"), degenerative signs on the retine and defective development on the edges (hypoplasia). The transparency of the lenses may be decreased. Refractive disorders – mainly myopia – nystagmus, astygmia, tear duct block (dacryostenosis), adulthood cataracts may occur. Teeth are frequently short, irregular teeth, but decay is less frequent. Parodontal issues often arise. Carpal bones and fingers are short. A so-called four-finger palmar crease is often seen. There is a visibly wide gap between big toes and the second toe. The pelvis is underdeveloped. The acetabular cup is shallow. Heart development disorders occur in about 40-60% of cases, which are mostly ventricular and atrial septum defects, open Botallo ducts, or less frequently valve problems, as well as issues with the arteria subclavia. The skin, especially on the neck and the back, are loose with lots of tissue present, dry and hyperkeratosis. The hair is thin and rare. Male patients often have relatively small penises and underdeveloped testicles. Women may occasionally conceive. Men are generally infertile. The central nervous system displays typically mental handicap of varying degrees.
The average IQ is between 25 and 50.
Muscle tone improves with time. Mental capabilities are usually better than would be expected based on IQ. Adults are as tall as healthy 15-year-olds. Eye-hand coordination is poor, but can be improved with proper training. Kids affected by Down syndrome are friendly, easy to manage, seek and are able to demonstrate love. They are sometimes surprisingly musical. Their life expectatncy is determined by the gravity of related, maily cardio-vascular conditions.

Compared to the healthy population, the life expectancy is as follows:

Down syndrome patients are more susceptible to infections, and a type of leuchemia is more frequent in their population. Their immune systems are weaker than the average.

As Down szndrome is caused multiple genetic disorders, it caanot be cured. Treatment is aimed at the management of associated medical conditions and mental development, as well as preparing the patient for independent life ("habilitation"), at which Hungary is recognized internationally.

By now, many Down syndrome patients can be developed to be capable of independent, balanced lifestyles. Children that used to be considered incapable of development (“idiots”) are capable of surprising performance as members of society. There are Down syndrome patients with drivers licenses in the US, and one of them is a popular character in a soap opera in Hungary.