Thursday, December 1, 2016
G6PD Deficiency - Family Genetics - Knowledge Is Power
This story begins about 4 1/2 years ago with the birth of Tamar's fourth child, Benaya.
Neonatal jaundice is a fairly common phenomenon, occurring in approximtely 50% of newborns. It usually lasts a week or two and during that time, depending on the severity, is treated with phototherapy.
All of Tamar's children were jaundiced and with them, it lasted for 3 to 4 weeks. Until the birth of Benaya, it was ascribed to ABO Incompatilility.
Hemolytic disease of the newborn (ABO)
From Wikipedia, the free encyclopedia
In ABO hemolytic disease of the newborn (also known as ABO HDN) maternal IgG antibodies with specificity for the ABO blood group system pass through the placenta to the fetal circulation where they can cause hemolysis of fetal red blood cells which can lead to fetal anemia and HDN. In contrast to Rh disease, about half of the cases of ABO HDN occur in a firstborn baby and ABO HDN does not become more severe after further pregnancies.
For some reason, it was decided to test Benaya for G6PD deficiency, and he tested positive.
At first, I assumed that he had inherited from his father, who is of Turkish and Egyptian descent, as the deficiency is known to be more common among Sephardim. However, when I did some internet research, I discovered that the gene for the deficiency is X-linked, which means that a male can only inherit it from his mother, which meant that Tamar had the gene in at least one X chromosome.
If Tamar had it, what about my other children?
I suggested that they have themselves tested, and they answered with a "you first, Ima!" So I had my self tested and I too tested positive. I could have inherited the gene for the deficiency from either my mother or my father, so the next time I visited Englewood, I accompanied my father to his medical checkup and asked the doctor to test my father. He, also, tested positive for the deficiency.
Then Lennie was tested and also came out positive, which meant that he had inherited it from my mother, and that both our parents are positive for the deficiency. I think that this is rather unusual in an Ashkenazi family.
Since my parents have lived with the deficiency for 90 some years and undoubtedly were exposed to at least some of the triggers, I assume that our family has a fairly mild variant of the deficiency, but still, it would be prudent to avoid the triggers listed in the article below.
So kids, stay away from those fava beans!
Glucose-6-phosphate dehydrogenase deficiency
From Wikipedia, the free encyclopedia
Glucose-6-phosphate dehydrogenase deficiency (G6PD deficiency), also known as favism (after the fava bean), is an X-linked recessive inborn error of metabolism that predisposes to hemolysis (spontaneous destruction of red blood cells) and resultant jaundice in response to a number of triggers, such as certain foods, illness, or medication. It is particularly common in people of Mediterranean and African origin. The condition is characterized by abnormally low levels of glucose-6-phosphate dehydrogenase, an enzyme involved in the pentose phosphate pathway that is especially important in the red blood cell. G6PD deficiency is the most common human enzyme defect.
There is no specific treatment, other than avoiding known triggers. In the United States, no genetic screening of prospective parents is recommended, as the symptoms only show in part of the carriers and when that is the case, they can be prevented or controlled, and as a result the disease generally has no impact on the lifespan of those affected. However, globally G6PD deficiency has resulted in 4,100 deaths in 2013 and 3,400 deaths in 1990.
Carriers of the G6PD allele appear to be protected to some extent against malaria, and in some cases affected males have shown complete immunity to the disease. This accounts for the persistence of the allele in certain populations in that it confers a selective advantage.
Signs and symptoms
Most individuals with G6PD deficiency are asymptomatic.
Symptomatic patients are almost exclusively male, due to the X-linked pattern of inheritance, but female carriers can be clinically affected due to unfavorable lyonization, where random inactivation of an X-chromosome in certain cells creates a population of G6PD-deficient red blood cells coexisting with normal red cells. A typical female with one affected X chromosome will show the deficiency in approximately half of her red blood cells. However, in rare cases, including double X deficiency, the ratio can be much more than half, making the individual almost as sensitive as a male.
Abnormal red blood cell breakdown (hemolysis) in G6PD deficiency can manifest in a number of ways, including the following:
Prolonged neonatal jaundice, possibly leading to kernicterus (arguably the most serious complication of G6PD deficiency)
Hemolytic crises in response to:
Illness (especially infections)
Certain drugs (see below)
Certain foods, most notably broad beans
Very severe crises can cause acute kidney failure
Favism may be formally defined as a hemolytic response to the consumption of broad beans. All individuals with favism show G6PD deficiency. However, not all individuals with G6PD deficiency show favism. Favism is known to be more prevalent in infants and children, and G6PD genetic variant can influence chemical sensitivity.Other than this, the specifics of the chemical relationship between favism and G6PD are not well understood.
Two variants (G6PD A− and G6PD Mediterranean) are the most common in human populations. G6PD A− has an occurrence of 10% of Africans and African-Americans while G6PD Mediterranean is prevalent in the Middle East. The known distribution of the disease is largely limited to people of Mediterranean origins (Spaniards, Italians, Greeks, Armenians, Jews and other Semitic peoples).Both variants are believed to stem from a strongly protective effect against Plasmodium falciparum and Plasmodium vivax malaria. It is particularly frequent in the Kurdish population (1 in 2 males have the condition and the same rate of females are carriers). It is also common in African American, Saudi, Sardinian males, some African populations, and Asian groups.
Carriers of the underlying mutation do not show any symptoms unless their red blood cells are exposed to certain triggers, which can be of three main types:
foods (fava beans is one of them),
medicines and other chemicals (see below), or
stress from a bacterial or viral infection.
In order to avoid the hemolytic anemia, G6PD carriers have to avoid a large number of drugs and foods. List of such "triggers" can be obtained from medical providers.
Many substances are potentially harmful to people with G6PD deficiency. Variation in response to these substances makes individual predictions difficult. Antimalarial drugs that can cause acute hemolysis in people with G6PD deficiency include primaquine, pamaquine, and chloroquine. There is evidence that other antimalarials may also exacerbate G6PD deficiency, but only at higher doses. Sulfonamides (such as sulfanilamide, sulfamethoxazole, and mafenide), thiazolesulfone, methylene blue, and naphthalene should also be avoided by people with G6PD deficiency as they antagonize folate synthesis, as should certain analgesics (such as phenazopyridine and acetanilide) and a few non-sulfa antibiotics (nalidixic acid, nitrofurantoin, isoniazid, dapsone, and furazolidone). Henna has been known to cause hemolytic crisis in G6PD-deficient infants.Rasburicase is also contraindicated in G6PD deficiency.
The most important measure is prevention – avoidance of the drugs and foods that cause hemolysis. Vaccination against some common pathogens (e.g. hepatitis A and hepatitis B) may prevent infection-induced attacks.
In the acute phase of hemolysis, blood transfusions might be necessary, or even dialysis in acute kidney failure. Blood transfusion is an important symptomatic measure, as the transfused red cells are generally not G6PD deficient and will live a normal lifespan in the recipient's circulation. Those affected should avoid drugs such as aspirin.
Some patients may benefit from removal of the spleen (splenectomy),as this is an important site of red cell destruction. Folic acid should be used in any disorder featuring a high red cell turnover. Although vitamin E and selenium have antioxidant properties, their use does not decrease the severity of G6PD deficiency.
G6PD deficiency is the most common human enzyme defect, being present in more than 400 million people worldwide.
G6PD deficiency resulted in 4,100 deaths in 2013 and 3,400 deaths in 1990. African, Middle Eastern and South Asian people are affected the most, including those who have these ancestries. A side effect of this disease is that it confers protection against malaria, in particular the form of malaria caused by Plasmodium falciparum, the most deadly form of malaria. A similar relationship exists between malaria and sickle-cell disease. One theory to explain this is that cells infected with the Plasmodium parasite are cleared more rapidly by the spleen. This phenomenon might give G6PD deficiency carriers an evolutionary advantage by increasing their fitness in malarial endemic environments. In vitro studies have shown that the Plasmodium falciparum is very sensitive to oxidative damage. This is the basis for another theory, that is that the genetic defect confers resistance due to the fact that the G6PD-deficient host has a higher level of oxidative agents that, while generally tolerable by the host, are deadly to the parasite.
G6PD-deficient individuals do not appear to acquire any illnesses more frequently than other people, and may have less risk than other people for acquiring ischemic heart disease and cerebrovascular disease.