Anatomy & Physiology IAnatomy & Physiology IResearch Presentation

Spina bifida

Ken McIntyreMontcalm Community College

Heather Wesp, Instructor

Spina bifidaSpina bifidaBetween the 15th and 28th day of pregnancy, the neural tube forms and subsequently becomes the brain and spinal column. Normally, during this first month of a pregnancy, the two sides of the spine join together to cover the spinal cord, spinal nerves and (meninges) the tissues covering the spinal cord.

Spina bifida is a neural tube defect (NTD) that constitute a group of malformations that result from failure of normal neural tube closure during the third and fourth week of embryologic development. (American Society of Human Genetics)

Spina bifida refers to any birth defect involving incomplete closure of the spine.

Myelomeningocele is the most common type of spina bifida. It is a neural tube defect in which the bones of the spine do not completely form, resulting in an incomplete spinal canal. This causes the spinal cord and meninges (the tissues covering the spinal cord) to stick out of the child's back. (PubMed Health)

Spina bifidaSpina bifida

Image from: ultrasound-images.com

Spina bifidaSpina bifida

Image from: University of Neurosurgery

Neural tube defects (NTDs) are a leading cause of infant mortality and morbidity involving the central nervous system.

Spina bifida (SB) is a common NTD with the defect occurring in the developing spinal cord resulting in various degrees of lower extremities paralysis. (American Society of Human Genetics)

The 3 main types of Spina bifida include:

OccultaMeningoceleMyelomeningocele

Rate of OccurrenceRate of Occurrence

Because Spina bifida refers to any birth defect that involves the incomplete closure of the spine, numbers indicating the rate of occurrence vary.

On average Spina bifida occurs in 3 of every 1,0000 births.

After a significant increase in the spina bifida rate from 1992 to 1995, there was a significant decline from 1995 to 1999. (CDC)

Although declines were not significant from 1999 to 2005, the rate for 2005, 17.96 per 100,000 live births, was the lowest ever reported. (CDC)

Image: CDC

Risk FactorsRisk Factors

Both environmental and genetic factors have been identified as contributing to the cause of spina bifida.

Race.

Spina bifida is more common among whites and Hispanics. (Mayo Clinic)

Family history of neural tube defects.

Couples who've had one child with a neural tube defect have a slightly higher chance of having another baby with the same defect. That risk increases if two previous children have been affected by the condition. In addition, a woman who was born with a neural tube defect, or who has a close relative with one, has a greater chance of giving birth to a child with spina bifida. However, most babies with spina bifida are born to parents with no known family history of the condition. (Mayo Clinic)

Folate deficiency.

Folate (vitamin B-9) is important to the healthy development of a fetus. Folate is the natural form of vitamin B-9. The synthetic form, found in supplements and fortified foods, is called folic acid. A folate deficiency increases the risk of spina bifida and other neural tube defects. (Mayo Clinic)

Some medications.

Anti-seizure medications, such as valproic acid (Depakene), seem to cause neural tube defects when taken during pregnancy, perhaps because they interfere with the body's ability to use folate and folic acid. (Mayo Clinic)

Diabetes.

Women with diabetes who don't control their blood sugar well have a higher risk of having a baby with spina bifida. (Mayo Clinic)

Obesity.

Pre-pregnancy obesity is associated with an increased risk of neural tube birth defects, including spina bifida. (Mayo Clinic)

Increased body temperature.

Some evidence suggests that increased body temperature (hyperthermia) in the early months of pregnancy may increase the risk of spina bifida. Elevating your core body temperature by about 3 to 4 degrees Fahrenheit above normal — about 2 degrees Celsius — due to fever or the use of saunas, hot tubs or tanning beds, has been associated with increased risk of spina bifida. (Mayo Clinic)

Symptoms of Spina BifidaSymptoms of Spina BifidaSymptoms

A newborn may have a sac sticking out of the mid to lower back. The doctor cannot see through the sac when shining a light behind it.

Symptoms include:

Loss of bladder or bowel control Partial or complete lack of sensation Partial or complete paralysis of the legs Weakness of the hips, legs, or feet of a newborn

Other symptoms may include:

Abnormal feet or legs, such as clubfoot Build up of fluid inside the skull (hydrocephalus) Hair at the back part of the pelvis called the sacral area Dimpling of the sacral area

(PubMed Health)

Signs of Spina bifidaSigns of Spina bifidaSigns

Prenatal screening can help diagnose this condition. During the second trimester, pregnant women can have a blood test called the quadruple screen. This test screens for myelomeningocele, Down syndrome, and other congenital diseases in the baby. Most women carrying a baby with spina bifida will have a higher-than-normal levels of a protein called maternal alpha fetoprotein (AFP).

If the quadruple screen test is positive, further testing is needed to confirm the diagnosis. Such tests may include:

Pregnancy ultrasound Amniocentesis

Myelomeningocele can be seen after the child is born. A neurologic examination may show that the child has loss of nerve-related functions below the defect. For example, watching how the infant responds to pinpricks at various locations may reveal where he or she can feel the sensations.

(PubMed Health)

Diagnosing Spina bifidaDiagnosing Spina bifida

If you're pregnant, prenatal screening tests to check for spina bifida and other birth defects. The tests aren't perfect. Even if the results are negative, there's still a small chance that spina bifida is present, and most mothers who have positive blood tests have normal babies. (Mayo Clinic)

Blood Tests

The first line test used to check for spina bifida (myelomeningocele) is the maternal serum alpha-fetoprotein (MSAFP) test. The blood is tested for alpha-fetoprotein (AFP) — a protein that's produced by the fetus. It's normal for a small amount of AFP to cross the placenta and enter the mother's bloodstream, but abnormally high levels of AFP suggest that the fetus has a neural tube defect. (Mayo Clinic)

Ultrasound

Many obstetricians rely on ultrasonography to screen for spina bifida. The information these images provide can help establish whether there's more than one fetus and can help confirm gestational age — two factors that can affect AFP levels. An advanced ultrasound can also detect signs of spina bifida, such as an open spine or particular features in your baby's brain that indicate spina bifida. (Mayo Clinic)

Diagnosing Spina bifidaDiagnosing Spina bifida

Amniocentesis

If a blood test shows high levels of AFP in your blood but the ultrasound is normal, your doctor may offer amniocentesis. During amniocentesis, your doctor uses a needle to remove a sample of fluid from the amniotic sac that surrounds the fetus. An analysis indicates the level of AFP present in the amniotic fluid.

A small amount of AFP is normally found in amniotic fluid. However, when an open neural tube defect is present, the amniotic fluid contains an elevated amount of AFP because the skin surrounding the baby's spine is gone and AFP leaks into the amniotic sac. (Mayo Clinic)

PrognosisPrognosisSpina bifida may cause no symptoms, or only minor physical disabilities, or it can result in severe physical disabilities. More frequently, it leads to severe physical and mental disabilities. Factors that affect the severity of complications include:

The size and location of the neural tube defect

Whether skin covers the affected area

Which spinal nerves come out of the affected area of the spinal cord

Treatments performed before and just after birth

Children with spina bifida can lead relatively active lives. The prognosis depends on the number and severity of abnormalities and associated complications. Most children with the disorder have normal intelligence and can walk, usually with assistive devices. (NINDS)

Additional problems may arise as children with spina bifida get older. (Mayo Clinic) My father didn't develop any complications until his mid 50's. And at almost 70 years old, he is still active for his age.

HomeostasisHomeostasis

Most homeostatic mechanisms in the body is based on negative feedback. Homeostasis is the body's way of maintaining certain set points that govern our bodies in order for them to function efficiently, use their resources effectively, and to remain healthy and viable.

The typical homeostatic mechanism involves 5 steps:

1. Stimulus – An external or internal change takes place;

2. Receptors – The body detects the external or internal change through certain sensory receptors;

3. Control Center – The brain receives the information from the sensory receptors and signals effectors;

4. Effectors – The body responds physically to correct the problem;

5. Response – The body returns to it's set point.

Homeostasis & Spina bifidaHomeostasis & Spina bifida

It appears that a glucose imbalance and deficiency of folate during pregnancy are the two major risk factors for NTDs.

The results in a recent study strongly support a critical role of glucose homeostasis maintaining genes as contributory to spina bifida susceptibility. Many of these genes have been associated with diseases (including NTDs) due to diabetes or glucose imbalance. The current findings support the hypothesis that maintenance of glucose homeostasis during pregnancy as a vitally important for normal neural tube development and implicate specific genes in this process. (American Society of Human Genetics)

Spina bifida disrupts homeostasis early in the development of the fetus. Proper development of the vertebral column and spinal canal is prevented, allowing internal organs to be exposed and damaged.

Because Spina bifida occurs as early as the first 2 weeks of fetaldevelopment, homeostasis is disrupted from the very beginning.

1. Stimulus – With Spina bifida, it appears the genes that determine the correct set point of blood glucose levels fail, leading to a cascading set of failures in neural tube development. The mutated genetic information in these genes may be a direct result of little or no vitamin B-9 in the mother's diet.

2. Receptors – The receptors in the pancreas detect blood glucose levels and relay that (incorrect) information to the control center (brain).

3. Control Center – When the brain does not receive the correct information from the pancreas, it does not send the correct signal back to the pancreas. If the correct set point is wrong or not known, the two hormones (insulin and glucagon) that are responsible for controlling the concentration of glucose in the blood are not released as needed.

4. Effector – In this case, the pancreas acts as both the primary receptor and effector.

5. Response – Again, in this case, the response is wrong and the body's “normal” set point is not maintained.

The Effects on Specific LevelsThe Effects on Specific Levels

The effects begin at the genetic level.

At the chemical level, folic acid works along with vitamin B12 and vitamin C to help the body break down, use, and create new proteins. This vitamin helps form red blood cells and helps to produce DNA. (NLM) When folic acid (Vitamin B-9) is lacking it can affect DNA synthesis and cell division.

The major effect on cells is they contain defective DNA, which result in an organ that does not develop and can not function as it is required in order to keep the body healthy.

Blood and bone are the major tissues effected. The blood contains more or less glucose than the typical body's set point and the blood can deliver too little glucose required for cellular respiration. Bone tissue is affected as it can not form properly.

The organs affected are:

• Skin. The skin fails to cover the spinal column which can allow foreign material into the body. The skin also helps protect the spinal cord.

The Effects ContinuedThe Effects ContinuedThe organs affected are:

• Bone. The vertebrae of the spinal column is the major means of protection for the spinal cord. Not only does the vertebrae of the spinal column form a harden, protective barrier around the spinal cord, it helps to stabilize it from moving too much.

• Spinal Cord. Without the protection and stabilization of the vertebrae and skin, the spinal cord protrudes from the body and is damaged and subject to additional damage.

The organ system most affected is the Central Nervous System due to the damage to the spinal cord. Without the protection of the spinal vertebrae and overlying tissues, the spinal cord is damaged and unable to function properly.

The effect on the human body as a whole can be mild to fatal. In some cases, people live full lives without any complications. In other cases, death occurs within minutes of being born.

PreventionPrevention

Folic acid supplements may help reduce the risk of neural tube defects such as myelomeningocele. It is recommended that any woman considering becoming pregnant take 0.4 mg of folic acid a day. Pregnant women need 1 mg per day.

It is important to remember that folic acid deficiencies must be corrected before becoming pregnant as the defects develop very early.

Prospective mothers may be screened to determine the amount of folic acid in their blood. (PubMed Health)

The best way to reduce your risk? Watch your weight, eat healthy and don't drink or smoke.

Image from: http://www.childrenshealthyfood.com

American Society of Human Genetics. "Glucose Homeostasis Genes and Spina Bifida Risk." Web. 17 Apr. 2011.

Centers for Disease Control and Prevention. (CDC) "CDC Data & Statistics | Feature: Trends in Spina Bifida, United States, 1991 - 2005." Web. 17 Apr. 2011.

National Institute of Neurological Disorders and Stroke (NINDS). "Spina Bifida Fact Sheet." Web. 18 Apr. 2011.

PubMed Health. "Myelomeningocele" Web. 17 Apr. 2011.

Spina Bifida Association "Mechanisms of Development (Pathogenesis)." Web. 17 Apr. 2011

Staff, Mayo Clinic. "Spina Bifida: Risk Factors - MayoClinic.com." Mayo Clinic. Web. 17 Apr. 2011.

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