Tay-Sachs disease

Tay Sachs Disease is a rare genetic disease in which the absence of a key protein results in the build-up of fatty substances. These fatty substances called gangliosides will become toxic in the body ultimately resulting in death around five years of age. This disease is not curable due to it being a result of a genetic mutation passed down by parents.

Gene Mutation

Tay Sachs is mostly a result of an in-frame deletion of 192 codons in the HEXA gene, located on chromosome 15q23. Although there are other causes of Tay Sachs disease, this seems to be the most common mutation (Gene bank accession number KR710352).

The HEXA gene is responsible for the production of a key enzyme called Beta-Hex0saminadase A. This enzyme, when normally synthesized is found in the lysosomes of nerve cells in your brain and spinal cord. Their function is to break down apart GM2 Gangliosides that accumulate in the cell. Their inability to synthesize these lipids results in the build-up of unmetabolizable and toxic GM2 Gangliosides in lysosomes.

How Is It Passed Down?

Since this disease is a result of a genetic mutation, you are not able to “catch” it from someone that has Tay Sachs. Instead, you must inherit it from your parents, just as you inherit your eye and hair color.

In this case, Tay Sachs is an autosomal recessive gene-disease. This means that both copies on both chromosomes have to have the gene mutation for this disease to be expressed. In other words, both of your parents must have one chromosome that has this mutation for an offspring to obtain this mutation. This also means that there is a 25% chance of inheriting this disease if two parents that are heterozygous for this mutation.

But, you may be asking why the parents that have this mutation do not know? Although it is possible to know you have this mutation if you take a PCR test, there is no other way to tell. People that are heterozygous for this mutation have no disease manifestation and can live their life normally.

So, why is this mutation so prominent? This mutation is thought to be a result of heterozygous evolution and advantageous results. People that are heterozygous for this mutation have an increased immune response to diseases like tuberculosis.

Symptoms

People that experience this disease will be a victim of numerous physical and mental disabilities. The most common include the loss of motor control due to the increase of GM2 Gangliosides building up in nerve cells. This destroys nonreproducible cells that function for motor control that is involuntary and voluntary.

Other symptoms include seizures, loss of vision and hearing, muscle weakness, and paralysis. There are treatments and medication to help combat these symptoms, however. Things such as medication, feeding tubes, physical therapy, and respiratory care can help manage and make these symptoms less frequent.

How Do You Identify Tay Sachs?

There are a few physical signs that may be a result of Tay Sachs. The most common is called Cherry red spots in the eyes. These are circular discolored areas in the posterior portion of the eye that is a result of lipid buildup and nerve damage. Other things such as the inability to lift their head at the proper age can also be signs. Genetic and blood tests can be used to further identify what problems are going on in the body, but it is always important to follow up with a professional.

People that are more likely to have this mutation include descents of:

  • Ashkenazi Jewish
  • French Canadian
  • Pennsylvania Dutch
  • Irish
  • Cajun

Eyes: How Do We See?

Most animals you can think of have eyes that help them process their environment. Eyes are one of the major senses of animals and without them, it is imminent that they will die in the wild. So, how does the eye work?

First, it is important to understand the anatomy of an eye. The light that is reflected off an object will first enter through the cornea. The cornea is the outer layer of your eye that helps focus light so you can see clearly. This clear layer is vital for proper vision and a deformity of the cornea will result in astigmatism (an irregular curve of the cornea).

After traveling through the cornea of the eye the light will pass directly between the iris in an area known as the pupil. The pupil is the dark center of your eye and the iris is the colored outer ring of your eye (brown, blue, etc.). The iris is responsible for adjusting to the intensity of the light. This means that if you were to look at an object that reflects a greater amount of light your pupils will constrict and limit the amount entering your eye. The opposite would happen in a dark area. This assures that the image being processed is not unseeable by brightness or darkness. A fun fact about your pupils is that both pupils will dilate and constrict together. This is called the pupillary reflex and is caused by the eyes connecting afferent (going towards the brain) nerves.

After passing through the pupil the light will then be focused for a second time by the lens. This lens works in conjunction with the cornea to assure that the light hits the retina correctly. Due to the light being focused twice by the cornea and lens the light is flipped upside down at this point. This image will be inverted again later.

When the light finally passes through the lens it travels through a clear gelatinous fluid called the vitreous. The vitreous is responsible for maintaining the shape of the eye as well as preventing damage to the retina. After passing through this fluid, light is projected onto the retina. The retina contains photoreceptors called rods and cones. Rods are responsible for processing stimuli at low levels of light. They do not process color and have low spatial acuity (ability to process 2 stimuli at a close distance). The cones are responsible for processing stimuli at high levels of light. They can process color and have high spatial acuity.

These rods and cones will send afferent signals back to the brain via the optic nerve. The brain will process this information in the optic lobe and flip the image so you can see it correctly.

The Femur: Stronger Than You Think

The femur is the bone the largest bone in your body and also one of the strongest bones. It is a vital support system for your entire body and bears the majority of weight and pressure. It is the only bone in the upper portion of your leg and is covered by mostly muscle. Being covered by muscle makes it one of the strongest areas of your body but, it causes complications if something goes wrong. If someone were to fracture their femur, completely, then the strong muscles of the quadriceps, hamstrings, and many others would pull in the separated parts of your bone. This would not only be extremely painful but extremely dangerous at the same time. See, along the femur runs a vital artery called the femoral artery. It supplies the legs with oxygenated blood to keep muscles active. When the femur is broken the muscles pulling on the bone will cause this artery to break. This can result in serious bleeding and can even be fatal.