Pyruvate kinase deficiency anaemia is a rare inherited blood disorder that causes red blood cells to break down too quickly, leading to a range of symptoms from mild tiredness to severe complications that can appear at any stage of life.
Understanding Pyruvate Kinase Deficiency Anaemia
Pyruvate kinase deficiency anaemia is an inherited condition that affects the red blood cells in your body. Red blood cells are responsible for carrying oxygen to all your tissues and organs, and they rely on an enzyme called pyruvate kinase to produce the energy they need to survive. An enzyme is simply a protein that helps chemical reactions happen in your body. When someone has this deficiency, their red blood cells cannot make enough energy, which causes them to break down much faster than normal red blood cells do.[1]
In healthy people, red blood cells typically live for about 120 days before they are naturally removed by the spleen and replaced with new ones. However, in people with pyruvate kinase deficiency, these cells may only survive for a few days or weeks. This premature breakdown is called hemolysis, and it leads to a condition known as hemolytic anemia, where the body does not have enough red blood cells to function properly.[2]
The condition is lifelong, meaning that people are born with it and will have it throughout their lives. However, the severity of symptoms varies enormously from person to person. Some individuals experience life-threatening complications as newborns, while others may have such mild symptoms that they are not diagnosed until adulthood, or they may have no noticeable symptoms at all.[3]
How Common Is Pyruvate Kinase Deficiency?
Pyruvate kinase deficiency is considered a rare disorder. The condition was first discovered in 1961 by a researcher named Valentine and colleagues, and since then, cases have been reported worldwide. However, determining exactly how common it is remains challenging because many mild cases may go undiagnosed.[1]
The estimated prevalence varies depending on the population studied. In Western populations, the condition is thought to affect between 3.2 and 8.5 people per million. Some reports suggest it may be as common as 1 in 20,000 people. More than 500 affected families have been identified globally, and research suggests the disorder may be underdiagnosed because people with mild symptoms may never be identified.[1][2]
The condition affects all ethnic groups and appears to affect men and women equally. However, certain populations have higher rates of the condition. For example, it is more common in the Old Order Amish communities in Pennsylvania and Ohio, as well as in Romani communities and certain areas in Brazil and Tunisia. These clusters can be explained by a founder effect, where mutations are traced back to specific couples who migrated to these areas, and by consanguinity, which means marriage between close relatives, increasing the chance that both parents carry the same faulty gene.[1][3]
What Causes Pyruvate Kinase Deficiency?
Pyruvate kinase deficiency is caused by mutations in a gene called PKLR. Your genes are like instruction manuals that tell your cells how to make proteins and enzymes. The PKLR gene, located on chromosome 1q21, provides instructions for making the pyruvate kinase enzyme that red blood cells need to produce energy.[1][2]
When there is a mutation or error in this gene, the body cannot produce enough functional pyruvate kinase enzyme. Red blood cells rely heavily on a process called glycolysis to generate energy. During glycolysis, glucose (a simple sugar) is broken down step by step to produce ATP (adenosine triphosphate), which is the cell’s main energy source. Pyruvate kinase catalyzes one of the final and most important steps in this process, converting a substance called phosphoenolpyruvate into pyruvate while producing ATP. This single step accounts for about 50 percent of all the ATP that red blood cells make.[1][4]
Scientists have identified about 300 different mutations in the PKLR gene that can cause pyruvate kinase deficiency. The majority of these are missense mutations, where a single building block of the gene is changed, leading to an altered protein. However, other types of mutations have also been reported, including frameshift mutations, deletions, and insertions. Different mutations can result in different levels of enzyme activity, which helps explain why symptoms vary so much between individuals.[1][6]
Pyruvate kinase deficiency follows an autosomal recessive inheritance pattern. This means that a person must inherit two faulty copies of the PKLR gene—one from each biological parent—to develop the condition. Parents who carry one faulty gene and one normal gene are called carriers. They typically do not show symptoms of the condition but can pass the faulty gene to their children. When both parents are carriers, there is a 25 percent chance with each pregnancy that their child will inherit both faulty genes and develop pyruvate kinase deficiency.[1][3]
Risk Factors for Pyruvate Kinase Deficiency
Since pyruvate kinase deficiency is an inherited genetic condition, you cannot develop it during your lifetime—you are either born with it or you are not. The primary risk factor is having parents who both carry a mutation in the PKLR gene. You cannot prevent inheriting this condition, as it is determined at conception.[3]
Certain populations and communities have a higher risk due to the increased frequency of specific PKLR mutations. People of northern European descent have been shown to have higher diagnosis rates. The condition is particularly prevalent in certain Amish communities in Pennsylvania and Ohio, where specific mutations have been traced back to founding members of these communities. Similarly, higher frequencies are found in Romani populations and in Mediterranean countries.[3][4]
Consanguinity, or marriage between closely related individuals, increases the likelihood that both parents carry the same genetic mutation, thereby raising the risk of having a child with an autosomal recessive condition like pyruvate kinase deficiency.[1]
Signs and Symptoms
The symptoms of pyruvate kinase deficiency can vary dramatically from person to person. The condition is present from birth, but when symptoms become noticeable depends on how severely the enzyme is affected. Some newborns show symptoms immediately after birth and require lifesaving treatment, while others may not notice any problems until childhood, adolescence, or even adulthood. In some cases, people may never develop noticeable symptoms and remain undiagnosed throughout their lives.[3][7]
Most symptoms are related to anemia, which occurs when there are not enough red blood cells to carry adequate oxygen to the body’s tissues. Common anemia symptoms include extreme tiredness or fatigue, which can be debilitating and affect daily activities. People may experience weakness, shortness of breath, especially during physical activity, and a rapid heartbeat as the heart works harder to pump oxygen-poor blood. Other signs include unusually pale skin, dizziness, headaches, and in children, difficulty keeping up with peers during play or exercise and slow growth.[3][8]
Other signs and symptoms result from the buildup of waste products when red blood cells break down prematurely. When red blood cells are destroyed, they release substances like iron and bilirubin. Excess bilirubin causes jaundice, which is a yellowing of the skin and the whites of the eyes. This can be particularly noticeable in newborns. Dark-colored urine is another sign, caused by bilirubin being filtered through the kidneys.[2][3]
Many people with pyruvate kinase deficiency develop an enlarged spleen, a condition called splenomegaly. The spleen is an organ that filters and removes damaged or old red blood cells from circulation. In pyruvate kinase deficiency, the spleen works much harder than normal because so many red blood cells are being destroyed, causing it to become larger. An enlarged spleen can sometimes be felt during a physical examination.[2][6]
Gallstones are another common complication. The buildup of bilirubin can form small, pebble-like deposits in the gallbladder or bile ducts, which may cause pain and require treatment. Iron overload can also occur, especially in people who receive frequent blood transfusions. Excess iron can accumulate in organs like the liver, heart, and pancreas, potentially causing damage over time.[2][8]
Symptoms can worsen during times of physiological stress, such as during infections, injuries, or pregnancy. Some people experience what is called an aplastic crisis, where the body temporarily stops making new red blood cells, causing severe anemia. Infants may be fussy, have trouble feeding, and show signs of low energy.[3][8]
How the Body Is Affected: Understanding the Changes
To understand how pyruvate kinase deficiency affects the body, it helps to know how red blood cells normally function. Mature red blood cells are unique because they lack a nucleus and mitochondria, which are structures found in most other cells. Without a nucleus, red blood cells cannot produce new proteins or repair damage. Without mitochondria, they cannot use oxygen to generate energy. This means red blood cells depend entirely on glycolysis, an anaerobic process that does not require oxygen, to produce the ATP they need to survive.[6]
Pyruvate kinase plays a crucial role in this energy production process. When the enzyme is deficient or not working properly, red blood cells cannot generate enough ATP. Without adequate energy, the cells cannot maintain their shape or function properly. The first systems to fail are the sodium-potassium pumps in the cell membrane, which normally keep the right balance of these minerals inside and outside the cell. When these pumps stop working, water rushes into the cell, causing it to swell and eventually burst. This premature destruction of red blood cells is what leads to hemolytic anemia.[6]
Interestingly, there is one unusual biochemical consequence of pyruvate kinase deficiency that may actually help patients tolerate their anemia better than expected. When the enzyme is deficient, a substance called 2,3-bisphosphoglycerate (2,3-DPG) accumulates in red blood cells. This molecule changes how hemoglobin binds to oxygen, making it easier for oxygen to be released to the body’s tissues. This compensatory mechanism means that even though people with pyruvate kinase deficiency have fewer red blood cells, those cells may deliver oxygen more efficiently than normal. As a result, some patients tolerate surprisingly low hemoglobin levels without severe symptoms.[6][7]
The spleen plays an important role in removing damaged red blood cells from circulation. In pyruvate kinase deficiency, the spleen works overtime because it is constantly filtering out the fragile, energy-depleted red blood cells. Over time, this extra work causes the spleen to enlarge. Young red blood cells, called reticulocytes, are particularly affected by the enzyme deficiency, which is why the condition can be especially severe in infants and young children.[1]
Prevention
Because pyruvate kinase deficiency is an inherited genetic condition, it cannot be prevented in individuals who inherit two faulty PKLR genes. However, there are steps that can help manage the condition and prevent complications once someone is diagnosed.[3]
For families with a known history of pyruvate kinase deficiency, genetic counseling can provide valuable information about the risk of passing the condition to children. Genetic testing can identify whether parents are carriers of PKLR mutations. In communities where the condition is more common, such as certain Amish populations, carrier screening may be particularly useful for family planning decisions.[1]
Prenatal testing is available if both parents are known carriers or if a previous child has been diagnosed with the condition. Tests such as amniocentesis or chorionic villus sampling can be performed during pregnancy to determine whether the baby has inherited the condition. These tests involve taking a sample of fluid or tissue from the womb to analyze the baby’s genes.[8]
Once diagnosed, certain lifestyle measures can help prevent complications and reduce symptoms. Maintaining good general health is important, including eating a balanced diet and staying physically active within individual limitations. Some people may need to avoid high-impact contact sports if they have significant splenomegaly, as an enlarged spleen is more vulnerable to injury.[11]
People with pyruvate kinase deficiency should receive supplemental folic acid and other B vitamins to support the increased production of red blood cells. The body uses these vitamins to make new blood cells, and people with chronic hemolysis need more than the average person.[11]
Vaccinations are particularly important for people who have had their spleen removed, as the spleen plays a key role in fighting infections. After splenectomy, individuals are at higher risk for serious infections from bacteria such as pneumococcus, meningococcus, and haemophilus. Vaccination against these bacteria, along with prompt treatment of any infection, is essential for preventing life-threatening complications.[19]
