Disclaimer: This article is for informational purposes only and is not intended to diagnose any conditions. LifeDNA does not provide diagnostic services for any conditions mentioned in this or any other article.

Ever step outside on a sunny day and feel an urge to sneeze? If so, you might be among the 18-35% of people who experience the photic sneeze reflex (PSR), also known as the “sun sneeze.” This reflex occurs when exposure to bright light, particularly sunlight, triggers sneezing. 

What is the Photic Sneeze Reflex?

The photic sneeze reflex is a phenomenon where sudden exposure to bright light, particularly sunlight, triggers sneezing. This reflex isn’t exclusive to sunlight; any abrupt transition to bright light, such as from a camera flash or stepping from a dim room into a well-lit space, may also cause it.

The medical term for this reflex is “autosomal dominant compelling helio-ophthalmic outburst” ACHOO syndrome, which simply means uncontrollable sneezing in response to sunlight. The reflex typically begins with a tickling sensation in the nose, followed by one or more sneezes when exposed to light.

Interestingly, the phenomenon wasn’t formally studied until the 1950s, when French researcher Jean Sedan observed that some of his patients sneezed in response to the light from his ophthalmoscope, a tool used to examine the eyes. He realized that various types of bright light could trigger sneezing.

What Causes a Photic Sneeze Reflex?

The photic sneeze reflex is a curious phenomenon where sneezing is triggered by sudden exposure to bright light. This reflex doesn’t occur just because of bright light alone, but rather due to a rapid change in light intensity. For example, stepping into direct sunlight after being in a dark room or driving through a tunnel on a sunny day and sneezing upon exiting are common triggers.

The exact cause of this reflex isn’t fully understood, but scientists have a few theories. One leading idea is that it involves a mix-up in the brain’s signaling system. When bright light hits the eyes, it stimulates the optic nerve, which helps us see. In people with the photic sneeze reflex, this stimulation might accidentally trigger the trigeminal nerve, which is responsible for sneezing. This overlap in nerve signals could be why a sudden burst of light may cause sneezing.

While the precise reason for this reflex and its purpose are still unclear, this explanation of nerve misfiring is the most commonly accepted one.

The Genetics Behind the Sneeze Reflex

Research indicates that this reflex is inherited and follows an autosomal dominant pattern. Researchers have identified several genetic markers that can help predict if you’re likely to sneeze in response to sunlight.  Among the genes associated with this trait are ZEB2, found on chromosome 2, and NRF2 found on chromosome 15, both of which are associated with nervous system function and sensitivity. Additionally this means if one parent has photic sneeze reflex (PSR), there’s a 50% chance their child will inherit it too. However, the exact genetic mechanisms underlying PSR are still being explored.

Scientists are still studying the genetic factors behind PSR. Variants known as single nucleotide polymorphisms (SNPs) in this gene may lead to a more sensitive nervous system, making someone more prone to PSR. SNPs in other genes play a role too, for example, having a C instead of a T-allele in the genetic marker rs10427522 which is in between genes SUMO3 and PTTG1IP is linked to a higher likelihood of developing PSR. 

Understanding the genetic causes of PSR is crucial as it could provide insights into human genetics and related conditions like photosensitive epilepsy. Studies of these genetic markers help in identifying the biological mechanisms behind the reflex and how they might be linked to other genetic disorders.

In addition to the broader implications for human genetics, research has also highlighted demographic patterns and other characteristics associated with PSR. According to a 1995 study on photic sneezing, the condition is more common in people who are white, and especially women and people assigned female at birth . Having a deviated septum may also have something to do with it.

To delve deeper into the genetics of PSR, researchers conducted a study with 3,417 Chinese participants, where 25.6% reported experiencing PSR. They discovered two important genetic markers: one previously known (rs10427255 on chromosome 2) and a new one (rs1032507 on chromosome 3, located in a non-protein coding RNA 971). The genetic variants either increased or decreased the chances of having PSR and can improve the ability to predict who might have PSR. 

Further research, focusing on the Japanese population. Researchers analyzed saliva samples from 11,409 participants who completed a web survey. After filtering the genetic data, 210,086 SNPs were studied. The prevalence of PSR in the group was found to be 3.2%. The study confirmed that genetic markers on chromosome 3, previously associated with PSR, were significant in this Japanese population as well. Additionally, two new genetic regions, on chromosomes 9 and 4 were identified with suggestive significance. The research also supported the involvement of two more SNPs, located on chromosomes 2 and 9, which had been previously associated with PRS in other populations. The results suggest that PSR is influenced by many genes and isn’t limited to one ethnic group.

Why Do Some People Sneeze While Others Don’t?

Not everyone experiences the photic sneeze reflex. This difference in who reacts to bright light adds an interesting twist to the reflex. Various factors, including genetics, play a role in whether someone will sneeze in response to bright light.

For instance, some people have genetic traits that make their nervous system more sensitive to stimuli, while others do not. In addition, traits like the color of  skin and eye color might influence the reflex. People with lighter eye colors might be more prone to photic sneezing. This is because lighter eyes let in more light, which could increase the chance of triggering the sneeze reflex. Similarly, genetic traits related to skin and eye pigmentation may interact with the reflex, influencing how frequently and intensely it occurs.

The severity of PSR may vary greatly among individuals. For some, exposure to bright light may cause multiple, uncontrollable sneezes, even in winter. Others may experience the reflex only occasionally or not at all. This variability means that it’s possible to inherit the photic sneeze reflex and not notice it, or it may manifest in different ways depending on the individual.

Can PSR develop later in life, or are you born with it?

Photic sneeze reflex (PSR) is typically considered a genetic trait, meaning you’re born with it. However, some people may not notice they have PSR until later, possibly because the reflex is mild or because they haven’t encountered strong enough light triggers until adulthood.

There’s no strong evidence that PSR suddenly develops in individuals who didn’t have it before, but it may become more noticeable in different circumstances or environments as you age.

Is the Photic Sneeze Reflex Related to Allergies or Other Conditions?

No, the photic sneeze reflex (PSR) is not related to allergies or other common conditions like a cold or sinus infection. While sneezing due to allergies is triggered by irritants like pollen or dust, PSR is specifically triggered by sudden exposure to bright light, particularly sunlight. The two involve different mechanisms—PSR is thought to be related to a mix-up in nerve signals involving the optic and trigeminal nerves, while allergic sneezing is caused by the immune system reacting to allergens.

However, someone with allergies may still have PSR, but the causes and triggers are unrelated.

What triggers PSR besides sunlight?

Besides sunlight, several other factors may trigger the photic sneeze reflex (PSR). These include:

1. Bright artificial lights: Sudden exposure to intense indoor lighting, such as camera flashes, may trigger PSR in some individuals.
2. Transitioning from darkness to light: Moving from a dimly lit environment to a brightly lit one may cause the reflex to occur.
3. Fluorescent lights: Certain types of bright, flickering lights, like fluorescent bulbs, may stimulate the sneeze reflex.
4. Reflections or glare: Bright reflections off surfaces like water, mirrors, or snow may act as triggers.
5. Medical lights: Lights used during medical or dental procedures, such as examination lights or operating room lamps, may also trigger PSR.

The common factor is sudden exposure to intense light, regardless of whether it’s natural or artificial.

Is Having a Photic Sneeze Reflex Dangerous?

Having a photic sneeze reflex (PSR) isn’t generally dangerous. Sneezing itself is a normal bodily function and doesn’t pose a threat. However, there are rare situations where it could be problematic.

The main concern is if you experience uncontrollable sneezing in situations where it could be risky. For example, sneezing while driving or operating heavy machinery could increase the chance of an accident. Similarly, sneezing during medical procedures, like dental work or eye exams, might be inconvenient or disruptive.

In rare cases, certain types of anesthesia, like propofol, or anesthetic injections near the eye during surgery may trigger PSR by stimulating the trigeminal nerve. This may be problematic, especially during delicate procedures.

If you have PSR, it’s helpful to mention it to your healthcare provider, particularly before any medical procedures. Letting them know in advance may help avoid any surprises or complications during treatment, ensuring that your reflex is managed properly when it matters most.

How Do You Deal with Photic Sneeze Reflex

There is no cure for the photic sneeze reflex and no medical treatment. Instead, treatment focuses on reducing sudden exposure to bright light, especially among people for whom such exposure could be dangerous, such as pilots or drivers. Managing the photic sneeze reflex involves simple strategies to minimize exposure to triggers and reduce its effects. Here are some practical ways to deal with it:

1. Wear Sunglasses: Using polarized or UV-blocking sunglasses may significantly reduce the intensity of sunlight exposure and help prevent the reflex from being triggered.
2. Gradual Light Adjustment: When moving from a dark to a brightly lit environment, allowing your eyes to adjust slowly to the light may reduce the likelihood of a sneezing episode. Try squinting or looking down briefly when stepping outside.
3. Avoid Direct Sunlight: When outdoors, avoiding direct sunlight by staying in shaded areas or using a hat with a brim may help minimize the impact of bright light on your eyes.
4. Eye Drops for Sensitivity: If light sensitivity is exacerbated by dry eyes, using moisturizing eye drops may help reduce the overall sensitivity to light and lessen sneezing triggers.
5. Awareness of Personal Triggers: Being mindful of the conditions that trigger your photic sneeze reflex, such as particular times of day when the sun is brighter or certain weather conditions, may help you anticipate and prevent sudden sneezing.

Though the reflex is typically harmless, these measures may help mitigate discomfort or inconvenience, especially in situations where a sneezing episode might be disruptive.

Summary

• The photic sneeze reflex (PSR), also known as “sun sneeze,” affects 18-35% of people and is triggered by sudden exposure to bright light, particularly sunlight.
• PSR may be caused by any abrupt transition to bright light, not just sunlight, such as stepping from a dim room into a well-lit space or from a camera flash.
• Genetic disposition to PSR follows an autosomal dominant inheritance pattern, meaning there’s a 50% chance of passing it to children if one parent has it.
• Research suggests that nerve misfiring is responsible for PSR, with bright light stimulating the optic nerve and accidentally triggering the trigeminal nerve, leading to sneezing.
• Genetic variants, such assingle nucleotide polymorphisms (SNPs), and specific genes like SCN5A, have been linked to PSR, but the exact genetic mechanism by these genetic factors remains unclear.
• PSR is more common in people who are white, and particularly in women and people assigned female at birth , and might be influenced by traits like eye color, with lighter eyes letting in more light.
• PSR may vary in severity, with some experiencing uncontrollable sneezing fits while others rarely notice it.
• PSR is generally harmless, but sneezing during risky situations, like driving or medical procedures, could be problematic.
• It’s helpful to inform healthcare providers of PSR, especially before medical procedures to avoid complications.
• Managing PSR involves wearing sunglasses, avoiding direct sunlight, gradually adjusting to light, and using eye drops for light sensitivity.
• There is no cure for PSR, but awareness of triggers and managing exposure may reduce its negative effects.

References

1. https://www.medicalnewstoday.com/articles/photic-sneeze-reflex#what-it-is 
2. https://link.springer.com/article/10.1007/s00405-016-4256-2 
3. https://www.healthline.com/health/photic-sneeze-reflex#takeaway
4. https://pubmed.ncbi.nlm.nih.gov/7673597/ 
5. https://www.ancestry.com/c/traits-learning-hub/photic-sneeze-reflex 
6. https://www.healthline.com/health/why-do-we-sneeze 
7. https://mendelbrain.com/en/photic-sneezing-genetic-origin-of-sneezing-when-looking-at-the-sun/
8. https://www.nature.com/articles/s41598-019-41551-0 

Disclaimer: This article is for informational purposes only and is not intended to diagnose any conditions. LifeDNA does not provide diagnostic services for any conditions mentioned in this or any other article. 

What are Blast Cells?

Blast cells are immature blood cells found in the bone marrow, where they develop into red blood cells, white blood cells, or platelets. Blast count refers to the number of blast cells. These immature cells play a crucial role in creating new blood cells in a process called hematopoiesis, which happens continuously throughout life. Normally, blast cells stay in the bone marrow until they mature. However, in certain health conditions, they can appear in the bloodstream too early, which is a sign that something is wrong with how the bone marrow is working.

Blast cells usually make up less than 5% of the total bone marrow cells. If they appear in the marrow in larger amounts, or in the bloodstream , it could mean the bone marrow is producing too many immature cells or not maturing them properly. This can lead to problems such as anemia (low red blood cell count), a higher risk of infections, or issues with blood clotting. Conditions like myelodysplastic syndrome (MDS) and leukemia often cause blasts to flood into the bloodstream, where they normally shouldn’t be found.

Blast cells come from hematopoietic stem cells, which are the “parent” cells in the bone marrow. These stem cells develop into one of two types of cells: myeloid or lymphoid. 

There are two main types of blast cells based on the cell lineage they are destined to follow:

• Myeloid Blasts: These immature cells develop into granulocytes (such as neutrophils, eosinophils, and basophils), monocytes, and other myeloid cells.
• Lymphoid Blasts: These blasts mature into lymphocytes, a key part of the immune system that includes B cells, T cells, and natural killer cells.

When doctors find a high level of blast cells in the blood, it’s a red flag for serious conditions like acute myelogenous leukemia (AML) or MDS. The type of blast cells—whether they are myeloid or lymphoid—helps doctors diagnose the exact disorder and determine the best course of treatment.

What is a Blast Count?

A blast count refers to the number of immature blood cells, or blast cells, present in the bone marrow or bloodstream. This count is typically expressed as a percentage of the total white blood cells in the bone marrow or blood sample. In healthy individuals, blast cells usually make up less than 5% of the bone marrow cells and are rarely found in the blood.

Why do Blasts Matter?

Blast cells are essential for producing healthy blood cells, but their significance goes beyond their normal role in hematopoiesis. Blasts matter because they can indicate the presence of severe conditions, such as hematopoietic neoplasms, which are disorders that affect blood cell production in the bone marrow. These conditions can disrupt the normal development of blood cells, leading to various health problems.

For example, acute leukemia is one of the most dangerous hematopoietic neoplasms where blasts rapidly multiply and take over the bone marrow, crowding out healthy blood cells. Without prompt treatment, this can quickly become life-threatening. Other disorders, like myelodysplastic syndromes (MDS) and chronic myeloproliferative disorders, also feature elevated blast levels and can gradually impair the bone marrow’s ability to function properly.

Blasts can also circulate in the bloodstream due to other factors such as severe infections, certain medications (like granulocyte colony-stimulating factor), or bone marrow-replacing processes. While not always a sign of cancer, the presence of circulating blasts should always be investigated, as it can point to serious underlying conditions.

How Do You Measure Blast Count?

Blast count is assessed through either a blood test or a bone marrow biopsy, depending on the patient’s condition. Both methods provide insight into how well the bone marrow is functioning.

1. Blood Test (CBC with Differential): A complete blood count (CBC) with differential can estimate blast count if blasts are present in the peripheral blood. Normally, blasts are not detectable in a healthy person’s blood. If found, even in small amounts, it may indicate a bone marrow issue. While less invasive, this test may not capture an accurate blast count if levels are low or confined to the marrow.
2. Bone Marrow Biopsy: This is the most accurate method for measuring blast count. A small bone marrow sample, usually from the pelvic bone, is examined to determine the percentage of blast cells. A healthy bone marrow contains less than 5% blasts. A higher count or blasts in the bloodstream can indicate serious blood disorders like acute myelogenous leukemia (AML) or myelodysplastic syndromes (MDS).

Why Blast Count Matter

Blast count is a crucial diagnostic tool for identifying and monitoring blood disorders. In healthy individuals, blasts should remain in the bone marrow. If they appear in the bloodstream or exceed 5% in the marrow, it may signal disorders like AML or MDS, which can disrupt normal blood cell development and lead to symptoms such as fatigue, infections, or abnormal bleeding.

Tracking blast count helps doctors evaluate disease progression and treatment effectiveness. A rising count may indicate worsening disease, while a declining count could suggest treatment success. Monitoring these changes enables more informed treatment decisions.

Blasts are measured either as a percentage of white blood cells or by their number per liter of blood. Regular monitoring is vital, especially in conditions like MDS, which can progress into more serious diseases.

What is the Normal Blast Count?

The normal blast count in healthy individuals typically comprises less than 5% of the total cells in the bone marrow. In peripheral blood, blasts should be zero or found in very low numbers.

What Does it Mean if You Have High/Low Blast Count?

High Blast Count

An elevated blast count can signal several health issues:

• Leukemia: High blast counts are commonly associated with leukemia, a cancer that impacts blood and bone marrow. The specific type of leukemia, such as acute myeloid leukemia (AML) or acute lymphoblastic leukemia (ALL), can often be identified based on the characteristics of the blast cells.
• Bone Marrow Disorders: Conditions like myelodysplastic syndromes (MDS) can lead to increased blast counts as the marrow struggles to produce mature blood cells.
• Other Malignancies: Certain cancers can cause secondary increases in blast counts due to their effects on the bone marrow.

To diagnose acute leukemia, criteria include having 20% or more blasts in the peripheral blood or bone marrow, or the presence of specific leukemia gene mutations.

Types of Leukemia and Their Characteristics

• Acute Promyelocytic Leukemia (APL): Recognized for its association with disseminated intravascular coagulation (DIC) and its unique treatment with all-trans retinoic acid (ATRA). Blasts in APL are large, have abundant cytoplasm, and display distinctive bilobed nuclei.
• Acute Monocytic Leukemia: Characterized by leukocytosis and monocytosis, with variable blast counts. Diagnosis requires 20% blasts or promonocytes in the blood or marrow.
• Lymphoblastic Leukemia: Lymphoblasts are small to medium-sized with scant cytoplasm and immature nuclei. Distinguishing lymphoblasts from lymphocytes can be challenging, often requiring flow cytometry.

High blast counts can indicate serious conditions, and monitoring these levels is essential for effective diagnosis and treatment planning.

Low Blast Count

A low or undetectable blast count in the peripheral blood or bone marrow generally indicates a healthy state. However, very low counts may suggest that the bone marrow is under severe stress or not producing enough blood cells.

In the context of leukemia, the presence of blasts in the blood is a crucial indicator. If more than 20% of cells in the blood are blasts, it likely points to leukemia. However, a lower percentage may occur if cancerous cells are trapped in the bone marrow, making them undetectable in blood tests.

Patients with leukemia may present with extremely high white blood cell counts, sometimes reaching between 100,000 to 400,000 per microliter of blood. Conversely, some may have low counts if immature cells are retained in the marrow.

A decreasing number of blasts typically indicates a positive response to treatment, while a rising count can signal a potential relapse.

What Indicates Remission?

Remission can vary based on individual circumstances. Two common categories include complete remission and complete remission with incomplete hematologic recovery. A patient may be considered in complete remission if they:

• No longer require regular transfusions
• Have a hemoglobin count that, while lower than normal, is above 7
• Show no blasts in the blood
• Maintain a platelet count over 100,000 (but below the normal range of 150,000)
• Have a neutrophil count exceeding 1,000

Monitoring these parameters is essential for determining remission status and guiding ongoing treatment.

The Role of Blast Count in MDS and AML: Insights from Genetic Factors

Blast count is a critical factor in the classification and treatment of myelodysplastic syndromes (MDS) and acute myeloid leukemia (AML). Recent studies have revealed the intricate relationship between blast percentages and genetic mutations, highlighting how these elements together impact prognosis and treatment strategies.

In a 2023 Study, researchers established a clear relationship between blast count and overall survival. Higher blast percentages generally correlated with poorer outcomes. However, the presence of certain genetic mutations, such as those affecting genes TP53 or FLT3 (a gene that produces a protein that helps form and grow new blood cells), could offer better prognostic information even in patients with elevated blast counts. This finding suggests that while blast count is essential, incorporating genetic profiling enhances the understanding of patient prognosis.

Another recent study focused on the interactions between blast count and specific mutations in MDS. For instance, patients with lower blast counts who also have the SF3B1 mutation demonstrated significantly better survival rates compared to those with higher blasts. This highlights the importance of genetic factors—such as the presence of SF3B1 mutations—in influencing outcomes, thereby suggesting that assessments should include both blast percentage and genetic mutation status for a more accurate prognosis.

Clearly, the relationship between blast count and genetic factors is important for managing MDS and AML. While blast percentage is a key part of classification, it’s evident that including genetic information—like mutations in genes TP53,  FLT3-ITD and SF3B1—can greatly improve prognosis and treatment plans. 

Summary

• Blast cells are immature blood cells in the bone marrow that develop into red and white blood cells or platelets.
• Blast cellsplay a vital role in continuous blood cell production through a process called hematopoiesis.
• Normally, blast cells stay in the bone marrow until they mature and make up less than 5% of total cells there.
• If blast cells appear in the bloodstream this indicates potential issues with bone marrow function.
• Increased blast cells are associated with  health problems like anemia, infections, and bleeding disorders.
• There are two main types of blast cells: myeloid blasts and lymphoid blasts.
• Myeloid blasts develop into various white myeloid blood cells, while lymphoid blasts mature into lymphocytes..
• A blast count measures the number of immature cells in the blood or bone marrow, expressed as a percentage.
• A normal blast count is less than 5% in the bone marrow and ideally zero in the blood.
• High blast counts often signal serious conditions like leukemia or myelodysplastic syndromes (MDS).
• Tracking blast count changes helps assess disease progression and treatment effectiveness.
• An elevated blast count, particularly over 20%, typically indicates leukemia.
• A low or absent blast count usually suggests healthy bone marrow, but very low counts may indicate systemic stress or inadequate blood cell production.
• Remission is assessed by the absence of blasts in the blood and stable blood cell counts.
• Genetic factors play a significant role in how blast counts affect prognosis and treatment strategies.
• Recent studies indicate that certain genetic mutations can influence survival rates in patients with MDS and acute myeloid leukemia (AML).
• Tailored treatment approaches are necessary as responses to therapies can differ between older and younger patients.
• Understanding both blast counts and genetic information is crucial for effective management of blood disorders.
• Proper monitoring can enhance patient outcomes and inform treatment decisions.
• Recent advancements in genetic testing may allow clinicians to predict patient outcomes more accurately, making personalized therapies important in treating blood cancers like MDS and AML. 
• Integrating genetic profiling with blast count analysis helps refine prognosis, ensuring more targeted and effective treatments that improve long-term survival and disease management.

References:

1. https://www.verywellhealth.com/overview-of-blast-cells-4114662
2. https://www.corpath.net/blasts
3. https://www.biron.com/en/glossary/blast-ratio-blast/
4. https://www.healthline.com/health/leukemia/leukemia-white-blood-cell-count-range#outlook
5. https://www.nature.com/articles/s41375-023-01855-7
6. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5486407/