Most cases of PWS are attributed to a spontaneous genetic error that occurs at or near the time of conception for unknown reasons. In a very small percentage of cases (2 percent or less), a genetic mutation that does not affect the parent is passed on to the child, and in these families more than one child may be affected. A PWS-like disorder can also be acquired after birth if the hypothalamic portion of the brain is damaged through injury or surgery.

It is estimated that one in 12,000 to 15,000 people has PWS. Although considered a "rare" disorder, Prader-Willi syndrome is one of the most common conditions seen in genetics clinics and is the most common genetic cause of obesity that has been identified. PWS is found in people of both sexes and all races.

Suspicion of the diagnosis is first assessed clinically, then confirmed by specialized genetic testing on a blood sample. Formal diagnostic criteria for the clinical recognition of PWS have been published (Holm et al, 1993), as have laboratory testing guidelines for PWS (ASHG, 1996).

A strong national organization of families and professionals, PWSA (USA) offers a toll-free helpline, a bimonthly member newsletter and numerous publications about PWS, a World Wide Web page (www.pwsausa.org), an annual family conference and scientific meeting, and chapters throughout the country to provide local family support and advocacy.

Genetics may play a role in PMDD. Studies have shown that identical twins are more likely to share the disorder (93%) than non-identical (fraternal) twins (44%), and daughters of mothers with PMDD are more likely to have it themselves. However, no specific genes have been identified to account for PMDD. It is best to simply say that genetics may put a woman at greater risk for developing the disorder.

There is a genetic factor in the development of allergic disease. If one parent has allergic disease, the estimated risk of a child to develop allergies is 48%; the child's estimated risk grows to 70% if both parents have a history of allergies.

Research shows that the risk for developing alcoholism does indeed run in families. The genes a person inherits partially explain this pattern, but lifestyle is also a factor. Currently, researchers are working to discover the actual genes that put people at risk for alcoholism. Your friends, the amount of stress in your life, and how readily available alcohol is also are factors that may increase your risk for alcoholism. But remember: Risk is not destiny.

Research shows that ADHD tends to run in families, so there are likely to be genetic influences. Children who have ADHD usually have at least one close relative who also has ADHD. And at least one–third of all fathers who had ADHD in their youth have children with ADHD. Even more convincing of a possible genetic link is that when one twin of an identical twin pair has the disorder, the other is likely to have it too.

In humans, there are two modes of inheritance: autosomal dominant and autosomal recessive (with at least two, and possibly three different autosomal dominant forms of PKD caused by different genes at different loci). To date, only the autosomal dominant form has been identified in cats. To quote Dr. DiBartola, Professor of Veterinary Clinical Sciences at The Ohio State University College of Veterinary Medicine, and Co-Editor of the Journal of Veterinary Internal Medicine (one of the Dr.

Genetics is a complex subject, and The Foundation Fighting Blindness has prepared another booklet, "The Inheritance of Retinal Degenerations," to explain this topic in detail. (This can be ordered by using The Foundation's Publication Order Form.) There are so many different forms of RP, which fall within one of three standard inheritance patterns. Each type of inheritance will create a different pattern of affected and unaffected family members.

Most cases of epilepsy are not inherited, although some types have a genetic basis. Most of these types are easily controlled with medication. Epilepsy syndromes with a genetic basis: Primary Generalized Epilepsies, Benign Rolandic Epilepsy, Nocturnal Frontal Lobe Epilepsy, Familial Temporal Lobe Epilepsy, Benign Familial Neonatal Seizures and Benign Familial Infantile Spasms.

Only 3 to 5% of cases are inherited; the rest arise as an accident of chromosome arrangement during meiosis. For details, see my essay on the origin of trisomy 21 or Dr. Paul Benke's essay on the types of DS, and the risk and recurrence risk of DS. No. Down syndrome occurs at conception, so nothing in the pregnancy can cause Down syndrome to occur. As for prior to conception, the research all shows that drug or alcohol use does not increase the risk of having a child with DS.

PWS is a complex genetic disorder that typically causes low muscle tone, short stature, incomplete sexual development, cognitive disabilities, problem behaviors, and a chronic feeling of hunger that can lead to excessive eating and life-threatening obesity.

Lupus is not inherited, but it is believed that the tendency to develop lupus is inherited. However, although a person may have the genetic markers for lupus, he/she will not get lupus unless it is triggered by something. Some people, who have the genetic markers, will never develop lupus.

Retinal degenerations affect men and women of all ages, races, cultures, and ethnic backgrounds. The broad range of retinal degenerative diseases affects at least six million Americans. Approximately 100,000 people in the United States are affected by retinitis pigmentosa or Usher syndrome, which is a variation of RP that also impairs hearing.

Research shows that the risk for developing alcoholism does indeed run in families. The genes a person inherits partially explain this pattern, but lifestyle is also a factor. Currently, researchers are working to discover the actual genes that put people at risk for alcoholism. Friends, the amount of stress in life, and how readily available alcohol is also are factors that may increase risk for alcoholism.1 But remember: Risk is not destiny.

MSS is autosomal recessive. It occurs with equal frequency in males and females. If both parents are carriers, there is a 25% chance that any child will have the disorder. In November 2005, a gene (SIL1) was identified that is responsible for about half of the known cases of MSS.

Allergies do tend to run in families. But for food allergy, it is common for only a single family member to be food allergic.

No. However in almost 50% of recorded cases there is a family history of hyperhidrosis. When a person is born with this condition he or she has primary hyperhidrosis while if hyperhidrosis develops as a result of another medical condition such as menopause or hyperthyroidism it is called secondary hyperhidrosis. In the latter instance the sweating is usually spread across larger areas of the body and not localized as in the case of primary hyperhidrosis as described in FAQ 1.

Yes! About half of children we see with bedwetting have a family history of the problem. Family studies have shown possible bedwetting genes on chromosomes 9, 12, 13, and 21.