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What is Lupus erythematosus and explain in detail?
Lupus erythematosus is a collection of autoimmune diseases in which the human immune system becomes hyperactive and attacks healthy tissues. Symptoms of these diseases can affect many different body systems, including joints, skin, kidneys, blood cells, heart, and lungs. The most common and most severe form is systemic lupus erythematosus.

Signs and symptoms
Symptoms vary from person to person, and may come and go. Almost everyone with lupus has joint pain and swelling. Some develop arthritis. Frequently affected joints are the fingers, hands, wrists, and knees.
Other common symptoms include:

chest pain during respiration
joint pain (stiffness and swelling)
painless oral ulcer
fatigue
weight loss
headaches
fever with no other cause
Skin lesions that appear worse after sun exposure
general discomfort, uneasiness, or ill feeling (malaise)
hair loss
sensitivity to sunlight
a "butterfly" facial rash, seen in about half of people with SLE
swollen lymph nodes

Photosensitivity
Photosensitivity is the amount to which an object reacts upon receiving photons especially in visible light. Photosensitivity is a known symptom of lupus, but its relationship to and influence on other aspects of the disease remain to be defined. Causes of photosensitivity may include:

change in autoantibody location
cytotoxicity
induction of apoptosis with autoantigens in apoptotic blebs
upregulation of adhesion molecules and cytokines
induction of nitric oxide synthase expression
ultraviolet-generated antigenic DNA

Genetics
It is typically believed that lupus is influenced by multiple genes. Lupus is usually influenced by gene polymorphisms, 30 of which have now been linked with the disorder. Some of these polymorphisms have been linked very tentatively, however, as the role that they play or the degree to which they influence the disease is unknown. Other genes that are commonly thought to be associated with lupus are those in the human leukocyte antigen (HLA) family. There have been several cases wherein a single gene influence appears to be present, but this is rare. When a single gene deficiency does cause lupus, it is usually attributed to the complement protein genes C1, C2, or C4. The influence of sex chromosomes and environmental factors are also noteworthy. Usually, these factors contribute to lupus by influencing the immune system. Several studies also indicate a potential association of lupus with mutations in DNA repair genes.

Age difference
Lupus can develop in people at any age, but it does most commonly at ages 15 to 44, with varying results. Typically, the manifestation of the disease tends to be more acute in those of younger age. Women are more likely to get it than men. Patients with juvenile-onset lupus are more vulnerable to mucocutaneous manifestations of the disease (alopecia, skin rash, and ulceration of the mucus membranes) than any other age group, and they are also more susceptible to evaluation of pulmonary artery pressure. However, patients with late-onset lupus have a much higher mortality rate. Nearly 50% of those with late-onset lupus die of their condition. Women who are of childbearing age are also particularly at risk.

Differences in ethnicity
Substantial data have been found to indicate that certain ethnic populations could be more at risk for lupus erythematosus and to have a better or worse prognosis. Asian, African, and Native Americans are more likely to get lupus than Caucasians. Caucasians seem generally to have a milder manifestation of the disease. Their survival rates after five years were typically around 94–96%, while patients of African and some Asian ethnicities had survival rates closer to 79–92%. The only documented ethnic group that had a higher survival rate than Caucasians was Koreans, who had survival rates nearer to 98%. Among Caucasians, the most common causes of death were complications involving the cardiovascular system, the respiratory system, and malignancies. Atherosclerotic cardiovascular disease is more prevalent in African Americans with lupus than in Caucasians with lupus.

Diagnosis
Diagnosis of lupus will vary from person to person. It is common to be diagnosed with other illnesses before a doctor can finally rule out lupus because a lot of the symptoms overlap with other common illness.Diagnosis of lupus erythematosis requires a physical examination, blood and urine tests, and a skin or kidney biopsy. Some other tests that may need to be run include:
Antinuclear antibody (ANA)
CBC with differential
Chest X-ray
Serum creatinine
Urinalysis

Classification
Lupus erythematosus may manifest as systemic disease or in a purely cutaneous form also known as incomplete lupus erythematosus