Uveitis specifically refers to inflammation of the middle layer of the eye, termed the “uvea” but in common usage may refer to any inflammatory process involving the interior of the eye, with inflammation specifically of the uvea termed iridocyclitis.

Uveitis is estimated to be responsible for approximately 10% of the blindness in the United States.[citation needed] Uveitis requires an urgent referral and thorough examination by an ophthalmologist, along with urgent treatment to control the inflammation.

Uveitis is usually categorized anatomically into anterior, intermediate, posterior and panuveitic forms.

Myriad conditions can lead to the development of uveitis, including systemic diseases as well as syndromes confined to the eye. In anterior uveitis, no specific diagnosis is made in approximately one-half of cases. However, anterior uveitis is often one of the syndromes associated with HLA-B27. Presence this type of HLA allele has a relative risk of evolving this disease by approximately 15%.[1]

Systemic disorders that can cause uveitis include: [2]

Masquerade syndromes are ophthalmic disorders that clinically present as either an anterior or posterior uveitis, but are not primarily inflammatory. The following are some of the most common:

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Urticaria pigmentosa (also known as “Generalized eruption of cutaneous mastocytosis (childhood type)”[1]:616 ) is the most common form of cutaneous mastocytosis. It is a rare disease caused by excessive numbers of mast cells in the skin that produce hives or lesions on the skin when irritated.

The majority of urticaria pigmentosa cases are caused by a point mutation at amino acid 816 of the proto-oncogene c-kit[2]. c-kit is a transmembrane protein which, when bound to Mast Cell Growth Factor (MCGF), signals the cell to divide. Mutations in position 816 of c-kit can result in a constant division signal being sent to the mast cells, resulting in abnormal proliferation. Different mutations have been linked to different onset times of the disease. For example, the Asp816Phe and Asp816Val mutations (the aspartate normally at position 816 in the c-kit protein has been replaced with phenylalanine or valine respectively) have been associated with early manifestation of the disease (mean age of onset: 1.3 and 5.9 months respectively). [3][4]

Urticaria pigmentosa is an orphan disease, affecting fewer than 200000 people in the United States.

The disease is most often diagnosed as an infant, when parents take their baby in for what appears to be bug bites. The bug bites are actually the clumps of mast cells. Doctors can confirm the presence of mast cells by rubbing the baby’s skin. If hives appear, it most likely signifies the presence of urticaria pigmentosa.

Urticaria Pigmentosa is characterized by excessive amounts of mast cells in the skin. Red or brown spots are often seen on the skin, typically around the chest and forehead. These mast cells, when irritated (e.g. by rubbing the skin, heat exposure), produce too much histamine, triggering an allergic reaction that leads to hives localized to the area of irritation, sometimes referred to as Darier’s sign. Severe itching usually follows, and scratching the area only serves to further symptoms. Symptoms can range from very mild (flushing, hives, no treatment needed) to life-threatening (vascular collapse).

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Urticaria (or hives) are a kind of skin rash notable for dark red, raised, itchy bumps. Hives are frequently caused by allergic reactions, however there are many non-allergic causes. For example, most cases of hives lasting less than 6 weeks (acute urticaria) are the result of an allergic trigger. Chronic urticaria (hives lasting longer than 6 weeks) are rarely due to an allergy. The majority of patients with chronic hives have an unknown (idiopathic) cause. Perhaps as many as 30-40% of patients with chronic idiopathic urticaria will, in fact, have an autoimmune cause. Acute viral infection is another common cause of acute urticaria (viral exanthem). Less common causes of hives include friction, pressure, temperature extremes, exercise, and sunlight. It may be true that hives are more common in those with fair skin.

Weals (raised areas surrounded by a red base) from urticaria can appear anywhere on the surface of the skin. Whether the trigger is allergic or non-allergic, there is a complex release of inflammatory mediators, including histamine from cutaneous mast cells, resulting in fluid leakage from superficial blood vessels. Weals may be pinpoint in size, or several inches in diameter. Angioedema is a related condition (also from allergic and non-allergic causes), though fluid leakage is from much deeper blood vessels. Individual hives that are painful, last >24 hours, or leave a bruise as they heal are more likely to be a more serious condition called urticaria pigmentosa. Hives caused by stroking the skin (often linear in appearance) is due to a benign condition called dermatographism.

The skin lesions of urticarial disease are caused by an inflammatory reaction in the skin, causing leakage of capillaries in the dermis, and resulting in an edema which persists until the interstitial fluid is absorbed into the surrounding cells.

Urticaria are caused by the release of histamine and other mediators of inflammation (cytokines) from cells in the skin. This process can be the result of an allergic or non-allergic reaction, differing in the eliciting mechanism of histamine release.

The rash that develops from poison ivy, poison oak, and poison sumac contact is commonly mistaken for urticaria. This rash is caused by contact with urushiol and results in a form of contact dermatitis called Urushiol-induced contact dermatitis. Urushiol is spread by contact, but can be washed off with a strong grease/oil dissolving detergent and cool water and rubbing ointments.

Angioedema is similar to urticaria,[4] but in angioedema, the swelling occurs in a lower layer of the dermis than it does in urticaria[5], as well as in the subcutis. This swelling can occur around the mouth, in the throat, in the abdomen, or in other locations. Urticaria and angioedema sometimes occur together in response to an allergen and is a concern in severe cases as angioedema of the throat can be fatal.

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Urocanic aciduria, also called urocanate hydratase deficiency or urocanase deficiency,[1] is an autosomal recessive metabolic disorder caused by a deficiency of the enzyme urocanase. It is a secondary disorder of histidine metabolism.[2]

The amino acid histidine, when catalyzed by the enzyme histidase, forms urocanic acid. Disruptions in this pathway, caused by a deficiency of histidase, is the underlying cause of histidinemia. This results in reduced levels of skin and serum urocanic acid, the primary indicator of insufficient histidase activity.

In urocanic aciduria, increased urocanic acid in the urine indicates a deficiency of the enzyme urocanase. This enzyme breaks down urocanic acid, forming formininoglutamic acid, and also forms imidazolonepropionic acid from trans-urocanic acid.

With normal to only slightly elevated levels of histidine present in the liver during urocanic aciduria, the only true metabolic indicator of the disorder can be found in the urine.[2]

Urocanic aciduria is thought to be relatively benign.[2] Although aggressive behavior and mental retardation have been reported with the disorder,[3] no definitive neurometabolic connection has yet been established.[2]

Urocanic aciduria has an autosomal recessive inheritance pattern, which means the defective gene is located on an autosome, and two copies of the gene – one copy inherited from each parent – are required in order to be born with the disorder. The parents of an individual with an autosomal recessive disorder both carry one copy of the defective gene, but are usually not affected by the disorder.

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Uremia is a term used to loosely describe the illness accompanying kidney failure (also called renal failure), in particular the nitrogenous waste products associated with the failure of this organ.[1]

In kidney failure, urea and other waste products, which are normally excreted into the urine, are retained in the blood. Early symptoms include anorexia and lethargy, and late symptoms can include decreased mental acuity and coma. It is usually diagnosed in kidney dialysis patients when the glomerular filtration rate, a measure of kidney function, is below 50% of normal.[2]

Azotemia is another word that refers to high levels of urea, but is used primarily when the abnormality can be measured chemically but is not yet so severe as to produce symptoms. Uremia can also result in fibrinous pericarditis. There are many dysfunctions caused by uremia affecting many systems of the body, such as blood (lower levels of erythropoietin), sex (lower levels of testosterone/estrogen) and bones (osteoporosis and metastatic calcifications).

Besides renal failure, the level of urea in the blood can also be increased by:

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Ulcerative colitis (Colitis ulcerosa, UC) is a form of inflammatory bowel disease (IBD). Ulcerative colitis is a form of colitis, a disease of the intestine, specifically the large intestine or colon, that includes characteristic ulcers, or open sores, in the colon. The main symptom of active disease is usually constant diarrhea mixed with blood, of gradual onset. Ulcerative colitis is, however, a systemic disease that affects many parts of the body outside the intestine. Because of the name, IBD is often confused with irritable bowel syndrome (“IBS”), a troublesome, but much less serious condition. Ulcerative colitis has similarities to Crohn’s disease, another form of IBD. Ulcerative colitis is an intermittent disease, with periods of exacerbated symptoms, and periods that are relatively symptom-free. Although the symptoms of ulcerative colitis can sometimes diminish on their own, the disease usually requires treatment to go into remission.

Ulcerative colitis occurs in 35-100 people for every 100,000 in the United States,[1] or less than 0.1% of the population. The disease tends to be more common in northern areas. Although ulcerative colitis has no known cause, there is a presumed genetic component to susceptibility. The disease may be triggered in a susceptible person by environmental factors. Although dietary modification may reduce the discomfort of a person with the disease, ulcerative colitis is not thought to be caused by dietary factors. Although ulcerative colitis is treated as though it were an autoimmune disease, there is no consensus that it is such. Treatment is with anti-inflammatory drugs, immunosuppression, and biological therapy targeting specific components of the immune response. Colectomy (partial or total removal of the large bowel through surgery) is occasionally necessary, and is considered to be a cure for the disease.

While the cause of ulcerative colitis is still unknown, several, possibly interrelated, causes have been suggested. Some think that the smallest illness could spark the disease.

A genetic component to the etiology of ulcerative colitis can be hypothesized based on the following:[2]

There are 12 regions of the genome which may be linked to ulcerative colitis. This includes chromosomes 16, 12, 6, 14, 5, 19, 1, 16, and 3 in the order of their discovery.[4] However, none of these loci has been consistently shown to be at fault, suggesting that the disorder arises from the combination of multiple genes. For example, chromosome band 1p36 is one such region thought to be linked to inflammatory bowel disease.[5] Some of the putative regions encode transporter proteins such as OCTN1 and OCTN2. Other potential regions involve cell scaffolding proteins such as the MAGUK family. There are even HLA associations which may be at work. In fact, this linkage on chromosome 6 may be the most convincing and consistent of the genetic candidates.[4]

Multiple autoimmune disorders have been recorded with the neurovisceral and cutaneous genetic porphyrias including ulcerative colitis, Crohn’s disease, celiac disease, dermatitis herpetiformis, diabetes, systemic and discoid lupus, rheumatoid arthritis, ankylosing spondylitis, scleroderma, Sjogren’s disease and scleritis. Physicians should be on high alert for porphyrias in families with autoimmune disorders and care must be taken with potential porphyrinogenic drugs, including sulfasalazine.

Many hypotheses have been raised for environmental contributants to the pathogenesis of ulcerative colitis. They include the following:

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Uhl anomaly was first described in 1952.[1] It is a very rare congenital heart disease (less than 100 cases 1900–1993) with a partial or total loss of the myocardial muscle in the right ventricle.

Three findings are enlarged right ventricular cavity without apical trabeculation with a thin hypokinetic ventricular wall.[2]

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Umbilical cord ulceration and intestinal atresia is a rare[1] congenital disease that leads to intestinal atresia, umbilical cord ulceration and severe intrauterine haemorrhage. Only 15 cases have so far been report[2] though newer studies are beginning to conclude that this disease has a higher incidence rate than has been previously reported.[3] A particular study has given intestinal atresia and umbilical cord ulceration a clear link after 5 such cases were reported at the time of publication.[4]

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Uncombable hair syndrome, also known as Pili trianguli et canaliculi[1]:639 , Spun-glass hair, and Cheveux incoiffable[2]:765 , is a rare structural anomaly of the hair with a variable degree of effect. It was discovered in the 1970s[3] It becomes apparent from as little as 3 months to up to 12 years.

The hair is normal in quantity and is usually silvery-blond or straw-colored. It is disorderly, it stands out from the scalp, and cannot be combed flat. The underlying structural anomaly is longitudinal grooving of the hair shaft, which appears triangular in cross section. There usually is no family history, though the characteristic hair shaft anomaly can be demonstrated in asymptomatic family members by scanning electron microscopy. To be noticeable, 50 % of hairs must be affected by the structural abnormality. Improvement often occurs in later childhood.[4][5] An autosomal dominant mode of inheritance has been suggested though a autosomal recessive pattern with varying degrees of penetrance has also been noted.[3][4] The stiffness of the uncombable hair has been reasoned to be due to the triangular form of the hair shaft in cross section. It has been suggested that the condition may result from premature keratinization of the inner root sheath.[4]

Other syndromes with hair abnormalities may also show features of uncombable hair syndrome such as Rapp-Hodgkin ectodermal dysplasia, loose anagen hair syndrome, EEC syndrome (ectodermal dysplasia, ectrodatyly and cleft lip/palate) and familial tricho-odonto-onchyial ectodermal dysplasia with syndactyly. However unlike these conditions, uncombable hair syndrome alone is not associated with physical, neurologic, or mental abnormalities.[3]

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Uniparental disomy (UPD) occurs when a person receives two copies of a chromosome, or part of a chromosome, from one parent and no copies from the other parent. [1]

UPD can occur as a random event during the formation of egg or sperm cells or may happen in early fetal development. It can also occur during trisomic rescue.

Most occurrences of UPD result in no phenotypical anomalies. However, if the UPD causing event happens during meiosis II, the genotype may include identical copies of the uniparental chromosome (isodisomy), leading to the manifestation of rare recessive disorders. UPD should be suspected in an individual manifesting a recessive disorder, where only one parent is a carrier.

Uniparental inheritance of imprinted genes can also result in phenotypical anomalies. Few imprinted genes have been identified, however uniparental inheritance of an imprinted gene can result in the loss of gene function which can lead to delayed development, mental retardation, or other medical problems.

Occasionally, all chromosomes will be inherited from one parent, due to either a sperm fertilizing an empty egg and duplicating itself, or a diploid egg that is not fertilized. The effect is similar to triploidy, with either a molar pregnancy with no embryo if only paternal genes are present, or an embryo with no placenta if only maternal genes are present. Neither condition ever results in a liveborn infant.

The first clinical case of UPD was reported in 1991 and involved a girl with cystic fibrosis and unusually short stature who carried two copies of maternal chromosome 7. Since 1991, out of the 47 possible disomies, 29 have been identified among individuals ascertained for medical reasons. This includes Chromosome 2, 5-11, 13-16, 21 and 22.[4]

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