The disorder is called Methemoglobin and there are people known as fugates in Kentucky - who over a century of isolation and inbreeding- became blue skinned. Look it up

Background: Methemoglobinemia is a condition in which the iron within hemoglobin is oxidized from the ferrous (Fe2+) state to the ferric (Fe3+) state, resulting in the inability to transport oxygen and carbon dioxide. Clinically, this condition causes cyanosis, often posing a diagnostic dilemma.

Methemoglobinemia in children usually results from exposure to oxidizing substances (such as nitrates or nitrites, aniline dyes, or medications including lidocaine, prilocaine, Pyridium, and others), or it is the result of inborn errors of metabolism (especially glucose-6-phosphate dehydrogenase deficiency and cytochrome b5 oxidase deficiency) or severe acidosis, which impairs the function of cytochrome b5 oxidase.


Pathophysiology: Hemoglobin molecules are tetrameric and contain iron within a porphyrin heme structure. The iron moiety in hemoglobin normally exists in the ferrous state Fe2+ in both oxyhemoglobin and deoxyhemoglobin and is capable of binding reversibly with oxygen only in this (ferrous) state. The oxidation of iron to the ferric state Fe3+ results in the formation of methemoglobin, which alters absorption and causes a brownish discoloration of the blood.

In healthy children, the ferric iron in methemoglobin is readily reduced to the ferrous state primarily through the function of cytochrome b5 oxidase (also referred to as methemoglobin reductase), which is present in erythrocytes and other cells. Patients who are deficient in cytochrome b5 reductase are particularly prone to methemoglobinemia, especially when exposed to oxidizing medications and other chemicals, including nitrates, nitrites, prilocaine and lidocaine, nitric oxide, and aniline dyes. Because methemoglobin is incapable of reversibly binding and transporting oxygen or carrying carbon dioxide, if it is present in significant amounts, methemoglobinemia can result in impaired oxygen delivery to (and carbon dioxide removal from) all tissue beds.

Cyanosis is commonly caused by either an excess of deoxygenated hemoglobin (usually in amounts >5 g/dL) or significant amounts of abnormal hemoglobins such as methemoglobin (>1.5 g/dL) or sulfhemoglobin (>0.5 g/dL), resulting in a grayish-bluish coloration of the skin and mucous membranes. Because the absolute amount of deoxygenated or abnormal hemoglobin rather than its percentage is required for cyanosis to be clinically evident, patients with moderate-to-severe anemia may not appear cyanotic, even with elevated percentages of deoxygenated or abnormal hemoglobins.

In healthy individuals, ongoing red blood cell exposure to a variety of oxidizing agents produces small amounts of methemoglobin; however, the concentration of methemoglobin (as a fraction of total hemoglobin) is maintained below 1% by a reduction enzyme system (mainly cytochrome b5 along with nicotinamide adenine dinucleotide [NADH] reductase), with additional protection provided by other systems including glutathione reductase and glucose-6-phosphate dehydrogenase. Methemoglobinemia occurs if the rate of oxidation is increased significantly and overwhelms the protective and reductive capacities of the cells, the structure of hemoglobin is altered and is resistant to reduction, or the rate of reduction of methemoglobin is decreased.

Methemoglobinemia may be acquired or congenital.


Acquired methemoglobinemia

Acquired methemoglobinemia is more common than congenital forms. Exposure to oxidant drugs and toxins in amounts that exceed the enzymatic reduction capacity of red blood cells precipitates symptoms of methemoglobinemia.

Acquired methemoglobinemia is more frequent in premature infants and infants younger than 4 months. The following factors may have a role in the higher incidence in this age group:

Hereditary methemoglobinemias may be divided into 2 categories, methemoglobinemia due to an altered form of hemoglobin (hemoglobin M) and enzyme deficiency (NADH reductase deficiency) that decreases the rate of reduction of iron in the hemoglobin molecule. Four types of hereditary methemoglobinemias are secondary to deficiency of NADH cytochrome b5 reductase. All are autosomal recessive disorders. Heterozygotes have 50% enzyme activity and no cyanosis. Homozygotes that have elevated methemoglobin levels above 1.5% have clinical cyanosis.


Type I: This is the most common variant, and the enzyme deficiency is limited to the erythrocytes causing cyanosis.

Type II: Widespread deficiency of the enzyme occurs in various tissues, including erythrocytes, liver, fibroblasts, and brain. It is associated with severe central nervous symptoms, including encephalopathy, microcephaly, hypertonia, athetosis, opisthotonus, strabismus, and mental and growth retardation. Cyanosis is evident at an early age.

Type III: Although the hemopoietic system (platelets, RBCs, white cells including lymphocytes and granulocytes) is involved, the only clinical consequence is cyanosis.

Type IV: Similar to type I, this type has isolated involvement of the erythrocytes, but it results in chronic cyanosis.
Deficiency of nicotinamide adenine dinucleotide phosphate (NADPH)–flavin reductase can also cause methemoglobinemia.

An amino acid substitution in or near the heme pocket affects the heme-globin bond, and the hemoglobin molecule becomes more stable in the oxidized form, resisting reduction. Several variants of hemoglobin M have been described, including hemoglobin Ms, hemoglobin MIwate, hemoglobin MBoston, hemoglobin MHyde Park, and hemoglobin MSaskatoon. These are usually autosomal dominant in nature. Alpha chain substitutions cause cyanosis at birth, whereas those in the beta chain become clinically apparent in infants aged 4-6 months.


Frequency:
In the US: Exact incidence is not known.
Internationally: Exact incidence is not known.


Mortality/Morbidity:

Patients with congenital methemoglobinemia are generally asymptomatic other than cyanosis. Life expectancy is normal unless the methemoglobin level is above 25-40%.
Acquired methemoglobinemia is usually mild but may be severe and rarely fatal, depending upon the cause.
Age: Hereditary forms appear early in life. Young infants, especially infants aged 3-4 months, are more susceptible to acquired methemoglobinemia.




CLINICAL Section 3 of 10
Author Information Introduction Clinical Differentials Workup Treatment Medication Follow-up Miscellaneous Bibliography
Physical:

Congenital methemoglobinemia

These patients are described as being more blue than sick.
Patients appear cyanotic with a diffuse slate-gray appearance.

Cyanosis is more easily observed on the nose, cheeks, fingers, toes, and in the mucous membranes, including the fundi, and it may be unrecognized for a long time in patients with more heavily pigmented skin. Clubbing is absent.

Methemoglobin levels of 10-20% are tolerated with no clinical symptoms, whereas levels of 30-40% may be associated with headaches and dyspnea, especially on exertion.

Patients with hemoglobin M disease with the alpha chain variant can present at birth with cyanosis, while patients with the beta chain variants present in the later half of infancy.
Causes:

Acquired: Exposure to various drugs or toxins may result in acquired methemoglobinemia. These include the following:

Nitrites
Aniline dyes
Silver nitrate
Nitroprusside
Antimalarials

Local anesthetics, such as Benzocaine, prilocaine, and lidocaine, particularly when applied to mucosa, such as during bronchoscopy, or after repeated cutaneous exposure to eutectic mixture of lidocaine-prilocaine (EMLA® cream) over a short period of time

Nitric and nitrous oxides
Vegetables (eg, spinach, beets, carrots) inadequately cooked or contaminated with bacteria

Hereditary: This may be due to the deficiency of NADH cytochrome b5 reductase or NADPH-flavin reductase or the presence of hemoglobin M.

An arterial blood sample from a patient with methemoglobinemia is characteristically chocolate brown. Blood that is cyanotic or dark in color due to cardiopulmonary disease turns red on exposure to oxygen, whereas blood with methemoglobin does not. A quick and easy bedside test is to bubble 100% oxygen in the tube containing the dark blood. If the blood remains dark, it most likely is due to the presence of methemoglobin.

Another simple test is to place 1-2 drops of patient blood on white filter paper, then evaluate for color change upon exposure to oxygen (this test can be accelerated by gently blowing supplemental oxygen onto the filter paper). Deoxygenated hemoglobin changes from dark red/violet to bright red, while methemoglobin remains brown.

Serum methemoglobin levels greater than 1% are considered abnormal, although higher levels are commonly encountered in smokers (and patients with long-term exposure to second-hand smoke). Symptomatic individuals usually have levels greater than 40-50%.

Serum levels of nitrites or other offending drugs may be determined.
NADH reductase levels should be checked.

The blood is exposed to light using a small probe placed on a finger or toe.

Light at wavelengths of 660 nm and 940 nm are used, and the ratio of absorption of light at each of these wavelengths is converted into oxygen saturation using calibration curves.

In a patient with methemoglobinemia, the severity of the cyanosis does not correspond to the pulse oximetry reading. The patient may appear extremely cyanotic but have a pulse oximetry reading in the high 80s...

if you want to read the rest of it, here's the link

http://www.emedicine.com/ped/topic1432.htm

And as a side note, blood isn't actually blue; deoxygenated blood is dark red

(Also, not to step on anyone's toes, but I think this topic is worth leaving open. There might be some other questions or comments regarding the condition.)

Its as real as your face :-)

honestly, who still uses "your lame thing here" anymore?

no one asked for your two cents if your going to be a dickweed about it. they are asking a question and in return, getting an answer. like it or not, you dont have to post.