Paget's disease may be caused by a slow virus infection (i.e., paramyxoviridae) present for many years before symptoms appear. Associated viral infections include respiratory syncytial virus, canine distemper virus, and the measles virus. However, recent evidence has cast some doubt upon the measles association. Laboratory contamination may have played a role in past studies linking paramyxovirus (e.g. measles) to Paget's disease.

The disease is progressive and slowly worsens with time, although people may remain minimally symptomatic. Treatment is aimed at controlling symptoms, but there is no cure. Any bone or bones can be affected, but Paget's disease occurs most frequently in the spine, skull, pelvis, femur, and lower legs.

Osteogenic sarcoma, a form of bone cancer, is a rare complication of Paget's disease occurring in less than one percent of those affected. The development of osteosarcoma may be suggested by the sudden onset or worsening pain.

The ultimate cause for these conditions is unknown, but the most commonly cited cause factors are rapid growth, heredity, trauma (or overuse), anatomic conformation, and dietary imbalances; however, only anatomic conformation and heredity are well supported by scientific literature. The way that the disease is initiated has been debated. Although failure of chondrocyte differentiation, formation of a fragile cartilage, failure of blood supply to the growth cartilage, and bone necrosis all have been proposed as the starting point in the pathogenesis, recent literature strongly supports failure of blood supply to growth cartilage as most likely.

Osteochondrosis is a family of orthopedic diseases of the joint that occur in children and adolescents and in rapidly growing animals, particularly pigs, horses, dogs, and broiler chickens. They are characterized by interruption of the blood supply of a bone, in particular to the epiphysis, followed by localized bony necrosis, and later, regrowth of the bone. This disorder is defined as a focal disturbance of endochondral ossification and is regarded as having a multifactorial cause, so no one thing accounts for all aspects of this disease.

VHL disease has an incidence of one in 36,000 births. There is over 90% penetrance by the age of 65. Age at diagnosis varies from infancy to age 60–70 years, with an average patient age at clinical diagnosis of 26 years.

Von Hippel–Lindau disease (VHL), also known as Familial cerebello retinal angiomatosis, is a rare genetic disorder with multisystem involvement. It is characterized by visceral cysts and benign tumors with potential for subsequent malignant transformation. It is a type of phakomatosis that results from a mutation in the von Hippel–Lindau tumor suppressor gene on chromosome 3p25.3.

Urbach–Wiethe disease is very rare; there are fewer than 300 reported cases in medical literature. Although Urbach–Wiethe disease can be found worldwide, almost a quarter of reported diagnoses are in South Africa. Many of these are in patients of Dutch, German, and Khoisan ancestry. This high frequency is thought to be due to the founder effect. Due to its recessive genetic cause and the ability to be a carrier of the disease without symptoms, Urbach–Wiethe disease often runs in families. In some regions of South Africa, up to one in 12 individuals may be carriers of the disease. Most of the case studies involving Urbach–Wiethe disease patients involve only one to three cases and these cases are often in the same family. Due to its low incidence, it is difficult to find a large enough number of cases to adequately study the disease.

Extramammary Paget's disease is usually seen in isolation and is associated with an underlying invasive malignancy about 12% of the time. It is associated with an underlying adnexal malignancy about 24% of the time. Paget's disease of the breast is almost always associated with an underlying invasive malignancy, i.e. breast cancer (e.g. mammary ductal carcinoma).

Urbach–Wiethe disease is typically not a life-threatening condition. The life expectancy of these patients is normal as long as the potential side effects of thickening mucosa, such as respiratory obstruction, are properly addressed. Although this may require a tracheostomy or carbon dioxide laser surgery, such steps can help ensure that individuals with Urbach–Wiethe disease are able to live a full life. Oral dimethyl sulfoxide (DMSO) has been shown to reduce skin lesions, helping to minimize discomfort for these individuals.

There are no currently known causes of this disease. There are studies currently proposing several theories of the causes which include inflammation of the adipose tissue, nervous system malfunction and endocrine malfunction. None of the theories that are currently proposed have been found viable. Since little is known about Dercum's disease, there are currently no known modes of prevention. Some hypotheses state that maintaining a healthy weight and diet can help prevent Dercum's although it has not been proven.

Dercum's disease can affect people of any gender and of any age. The majority of cases are linked to women between the ages of 45 and 60, who are overweight and postmenopausal. Due to the difficulty of diagnosis of this disease, many cases are underreported or misdiagnosed and it is difficult to understand what part of the population is affected by it the most.

Paget's disease of the vulva, a rare disease, may be a primary lesion or associated with adenocarcinoma originating from local organs such as the Bartholin gland, the urethra, or the rectum and thus be secondary. Patients tend to be postmenopausal.

Paget's disease of the penis may also be primary or secondary, and is even rarer than genital Paget’s disease in women. At least one case has been misdiagnosed as Bowen's disease. Isolated Paget's disease of the penis is extremely rare.

This disease is more common in women and an association with the gene FLT4 has been described. FLT4 codes for VEGFR-3, which is implicated in development of the lymphatic system.

Milroy's disease is also known as primary or hereditary lymphedema type 1A or early onset lymphedema.

It is a very rare disease with only about 200 cases reported in the medical literature. Milroy's disease is an autosomal dominant condition caused by a mutation in the FLT4 gene which encodes of the vascular endothelial growth factor receptor 3 (VEGFR-3) gene located on the long arm (q) on chromosome 5 (5q35.3).

In contrast to Milroy's disease (early onset lymphedema type 1A,) which typically has its onset of swelling and edema at birth or during early infancy, hereditary lymphedema type II, known as Meige disease, has its onset around the time of puberty. Meige disease is also an autosomal dominant disease. It has been linked to a mutations in the ‘forkhead’ family transcription factor (FOXC2) gene located on the long arm of chromosome 16 (16q24.3). About 2000 cases have been identified. A third type of hereditary lymphedema, that has an onset after the age of 35 is known as lymph-edema tarda.

The causes of Kyrle disease are unclear and can be idiopathic. The only correlation that has shown light is the frequent association with an underlying disorder, such as, diabetes mellitus, chronic renal failure, hyperlipoproteinemia, hepatic abnormalities, and congestive heart failure. However, there had been cases where Kyrle disease was seen without any conjunction with the previous mentioned disorders. Due to the causes of Kyrle disease is unknown, the best way to prevent the disease is to prevent the disorders that are usually reported in conjunction with it.

Morbidity and mortality range from both extremes as the significance correlate with the underlying systemic disease.

It is associated with LAMP2. The status of this condition as a GSD has been disputed.

Milroy's disease (MD) is a familial disease characterized by lymphedema, commonly in the legs, caused by congenital abnormalities in the lymphatic system. Disruption of the normal drainage of lymph leads to fluid accumulation and hypertrophy of soft tissues. It is also known as Milroy disease, Nonne-Milroy-Meige syndrome and hereditary lymphedema.

It was named by Sir William Osler for William Milroy, a Canadian physician, who described a case in 1892, though it was first described by Rudolf Virchow in 1863.

Life expectancy with Fabry disease for males was 58.2 years, compared with 74.7 years in the general population, and for females 75.4 years compared with 80.0 years in the general population, according to registry data from 2001 to 2008. The most common cause of death was cardiovascular disease, and most of those had received kidney replacements.

Although the genetic cause of Danon Disease is known, the mechanism of disease is not well understood. Danon disease involves a genetic defect (mutation) in a gene called LAMP2, which results in a change to the normal protein structure. While the function of the "LAMP2" gene is not well understood, it is known that LAMP2 protein is primarily located in small structures within cells called lysosomes.

Infants with Schindler disease tend to die within 4 years of birth, therefore, treatment for this form of the disease is mostly palliative. However, Type II Schindler disease, with its late onset of symptoms, is not characterized by neurological degeneration. There is no known cure for Schindler disease, but bone marrow transplants have been trialed, as they have been successful in curing other glycoprotein disorders.

Adiposis dolorosa, also known as Dercum's disease or Anders disease, is a rare condition characterized by generalized obesity and fatty tumors in the adipose tissue. The tumors are normally painful and found in multiples on the extremities. The cause and mechanism of Dercum's disease remains unknown. Possible causes include nervous system dysfunction, mechanical pressure on nerves, adipose tissue dysfunction, and trauma.

Dercum's disease was first described at Jefferson Medical College by neurologist Francis Xavier Dercum in 1892.

There is no specific treatment for Farber disease. Corticosteroids may be prescribed to relieve pain. Bone marrow transplants may improve granulomas (small masses of inflamed tissue) on patients with little or no lung or nervous system complications. Older patients may have granulomas surgically reduced or removed.

Most children with Farber disease die by age 2, usually from lung disease. In one of the most severe forms of the disease, an enlarged liver and spleen (hepatosplenomegaly) can be diagnosed soon after birth. Children born with this form of the disease usually die within 6 months.

In infantile Krabbe disease, death usually occurs in early childhood. A 2011 study found 1, 2, 3 year survival rates of 60%, 26%, and 14%, respectively. A few survived for longer and one was still alive at age 13. Patients with late-onset Krabbe disease tend to have a slower progression of the disease and live significantly longer.

Many forms of cystic kidney disease can be detected in children prior to birth. Abnormalities which only affect one kidney are unlikely to cause a problem with the healthy arrival of a baby. Abnormalities which affect both kidneys can have an effect on the baby's amniotic fluid volume which can in turn lead to problems with lung development. Some forms of obstruction can be very hard to differentiate from cystic renal disease on early scans.

The disease appears to be progressive in nature. The Fields twins started having problems when they were four years old. By the time they had reached the age of nine, they were having difficulty walking and needed frames to assist them with walking. Their muscles have been gradually deteriorating over time. The disease affects the twins' nerves, causing them to make involuntary muscle movements such as trembling in the hands.

The extent of the disease is still unknown as the two women are only 21. However, the disease has had no apparent effect on their brains or personalities. Doctors do not know if the disease is fatal and, if so, what the life expectancy of one with this disease is. If the cause of the disease is genetic, there is a chance that the twins could pass it on to their future children.