METHEMOGLOBINEMIA- BLUE SKINNED PEOPLE

Methemoglobinemia is a disorder that describes blood with an abnormally high concentration of methemoglobin— a bluish-brown hemoglobin that carries iron in the ferric state. This leads to reduced oxygen levels throughout the body, because red blood cells lose their ability to release oxygen to tissues. 


Methemoglobin is a form of hemoglobin that contains ferric [Fe³⁺] iron and has a decreased ability to bind oxygen. However, the ferric iron has an increased affinity for bound oxygen.The binding of oxygen to methemoglobin results in an increased affinity of oxygen to the three other heme sites (that are still ferrous) within the same tetrameric hemoglobin unit. This leads to an overall reduced ability of the red blood cell to release oxygen to tissues. 
With methemoglobinemia, hypoxia — the deprivation of oxygen — of organs and tissue may occur. 

Signs and symptoms: of methemoglobin >1%) include shortness of breath, cyanosis, mental status changes (~50%), headache, fatigue, exercise intolerance, dizziness and loss of consciousness.

Patients with severe methemoglobinemia (methemoglobin >50%) may exhibit seizures, coma and death (>70%).Healthy people may not have many symptoms with methemoglobin levels < 15%. 

However, patients with comorbidities such as anemia, cardiovascular disease, lung disease, sepsis, or presence of other abnormal hemoglobin species (e.g. carboxyhemoglobin, sulfhemoglobin or sickle hemoglobin) may experience moderate to severe symptoms at much lower levels (as low as 5-8%).

TYPES

1. Acquired : Methemoglobinemia may be acquired.Classical drug causes of methemoglobinemia include antibiotics (trimethoprim, sulfonamide), local anesthetics.

2. Congenital: Due to a deficiency of the enzyme diaphorase I (NADH methemoglobin reductase), methemoglobin levels rise and the blood of met-Hb patients has reduced oxygen-carrying capacity. Instead of being red in color, the arterial blood of met-Hb patients is brown. This results in the skin of Caucasian patients gaining a bluish hue. Hereditary met-Hb is caused by a recessive gene. If only one parent has this gene, offspring will have normal-hued skin, but if both parents carry the gene there is a chance the offspring will have blue-hued skin.

Another cause of congenital methemoglobinemia is seen in patients with abnormal hemoglobin variants such as hemoglobin M (HbM), or hemoglobin H (HbH), which are not amenable to reduction despite intact enzyme systems.

Methemoglobinemia can also arise in patients with pyruvate kinase deficiency due to impaired production of NADH – the essential cofactor for diaphorase I. Similarly, patients with Glucose-6-phosphate dehydrogenase (G6PD) deficiency may have impaired production of another co-factor,NADPH.

  

YOU CAN READ ABOUT THE FUGATE FAMILY: THE BLUE PEOPLE OF TROUBLESOME CREEK WHOSE PROGENY AROSE FROM A MARRIED COUPLE WHO BOTH POSSESS THE RECESSIVE GENE FOR METHEMOGLOBINEMIA.





SOURCE: THOUGHTCATALOG
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