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What is Severe Primary IGF-1 Deficiency?

Severe Primary Insulin-like Growth Factor (IGF-1) Deficiency is defined by:

  • Height SDS* is ≤ -3.0
  • IGF-1 concentration SDS ≤ -3.0
  • Growth hormone is normal or elevated

*SDS is the standard deviation score. SDS refers to the amount a value differs from the average value for a given measure. A negative value is below the mean value.

IGF-1 is Vital for Growth

IGF-1 is Vital for Growth

IGF-1 is a naturally occurring hormone that is vital in promoting growth. If your child is diagnosed with short stature and the cause is not known (idiopathic) or they do not show improvement after receiving growth hormone therapy they may have a lack of IGF-1 (Insulin-like Growth Factor deficiency).

Importantly, if your child’s IGF-1 levels are very low (i.e. severe) but their growth hormone levels are normal or even elevated, this could be the main reason why they are shorter than almost all other children of the same age and gender. Your child may have Severe Primary IGF-1 Deficiency or SPIGFD.

Diagnosing and Testing

Diagnosing and Testing

Some of the tests that may be used to evaluate a child with short stature are described in this section. Click on the link below to read a detailed description of each.

History and examination

History and examination

Often, one of the first steps in trying to find out why a child is shorter than expected for their age is for the doctor to take a medical history and perform a physical examination.

Your doctor may ask about your child’s and family’s health history. They may also ask you how much and how fast your child has grown in the past; if your child has received any particular medications that might have affected their growth; and other questions to help rule out any other conditions.

Your child’s height and weight will likely be measured.

Growth assessment

Growth assessment

A growth chart may be used to determine your child’s growth. Growth charts are one of the tools that doctors can use to see if a child is growing as expected for their age and gender. There are different charts for boys and girls and also charts that help assess a child’s growth related to both their height and weight.

An example of a growth chart can be seen below. In this example, the expected average height is shown as a solid dark green line. Heights above and below this average are given a number to show how much they vary from the average height. This difference is called standard deviation.

Growth Charts Can Help Diagnose Severe Primary IGF-1 Deficiency

Height Chart

*SDS, standard deviation score. Data and formula from
Centers for Disease Control and Prevention.

In addition to measuring your child’s height, parents’ height may also be recorded.

This measurement is used to help doctors calculate what a child’s expected height could be. Although it is good to measure regularly your child’s at home, it may be more accurate to have measurements taken at the doctor’s office to ensure consistency.

Height velocity

Height velocity

The speed at which your child is growing is known as the height velocity. This can be calculated by measuring your child’s height at regular intervals over a fixed time frame. Knowing a child’s height velocity can help a doctor determine if your child is growing at an expected rate.

IGF-1 blood test

IGF-1 blood test

If your doctor suspects your child has a growth disorder, a blood sample is likely to be taken and sent to a laboratory to measure levels of important hormones that influence growth, such as growth hormone and IGF-1.

If initial results show that there are low levels of growth hormone your doctor may suggest beginning treatment to increase the levels of this hormone. If your child is still not growing as expected, your doctor may also measure levels of IGF-1 in the blood to see if they may need to be supplemented. If IGF-1 treatment is considered, then IGF-1 levels may need to be measured periodically.

GH Stimulation Test

GH Stimulation Test

If tests show that IGF-1 levels are indeed low, a Growth Hormone (GH) stimulation test may be performed next, to see if your child has Severe Primary IGF-1 Deficiency.

A GH stimulation test will take place in the doctor’s office and your child will be given a medicine (usually by injection) that will stimulate their body to produce GH. Blood samples will be taken at regular intervals during this test. The samples will be sent to a laboratory for analysis and the results will let the doctor know how much GH your child released during the course of the test. Their results can then be compared to what would be expected for other children their age.

Severe Primary IGF-1 Deficiency occurs when GH levels in the blood are normal or even higher than might be expected and IGF-1 levels are very low (≤ -3.0 SDS), and their height falls more than three standard deviations below the average height for their age (i.e. ≤ -3 SDS).

Your child’s doctor will let you know what levels of IGF-1 and GH are considered normal.

Bone Age Study

Bone Age Study

A bone age study is a way for doctors to assess how a child’s skeletal system is maturing in comparison to the expected development for their age and gender. It traditionally involves taking a single X-ray of the left wrist and hand and comparing the images obtained to a standard set of images.

Children who have familial short stature or idiopathic short stature often have a bone age equivalent to their chronologic age. By contrast, those with a delay in growth due to puberty or hormonal disorders often have a bone age that is lower than their chronological age.

Specialized imaging

Specialized imaging

Magnetic Resonance Imaging (MRI) is a special imaging method that may be performed on children with suspected growth disorders to see if there are any tumors or structural abnormalities in the central nervous system that might be responsible for their short stature.

Advocating for Your Child

Advocating for Your Child

Caring for a child with a health issue can be challenging at times. Doctors and nurses are there to help you, and together, you will make the final decisions regarding your child’s health. It can take time to get to the right diagnosis and there may be many visits and tests before you get the answers you need.

You can help by being proactive and engaged in your child’s treatment. Ask your child’s doctor or nurse for information about your child’s condition and find out where you can learn more about the latest developments in diagnosis and treatment.

See the Support and Resources section of this website for educational materials and links to information on Severe Primary IGF-1 Deficiency.

Important Safety Information

Who Should Not Receive INCRELEX®?

Your child should not receive INCRELEX® if your child: is allergic to mecasermin or any of the ingredients in INCRELEX®; has finished growing; has any cancerous tumors or growths; or has a history of cancer. Your child should never receive INCRELEX® through a vein.

What Should I Tell My Child’s Doctor Before My Child Starts INCRELEX®?

Tell your child’s doctor about all of your child’s medical conditions, including if your child: has diabetes; a curved spine (scoliosis); or is pregnant or breast-feeding.

Tell your child’s doctor about all the medicines (prescription and over-the-counter), vitamins, and herbal supplements your child takes. Especially tell your child’s doctor if your child takes insulin or other anti-diabetes medicines; a change in dose maybe needed.

What are the Possible Side Effects of INCRELEX®?
INCRELEX® may cause serious side effects, including:

  • Low blood sugar (hypoglycemia). INCRELEX® may lower blood sugar levels. It is important to only give your child INCRELEX® 20 minutes before or 20 minutes after a meal or snack to reduce the chances of low blood sugar. Do not give your child INCRELEX® if your child cannot eat. Signs of low blood sugar include: dizziness; tiredness; restlessness; hunger; irritability; trouble concentrating; sweating; nausea; and fast or irregular heartbeat. Severe low blood sugar may cause unconsciousness, seizures, or death. Your child should avoid participating in high risk activities (e.g. driving, exercise, etc.) within 2 to 3 hours after the INCRELEX® injection, especially at the beginning of treatment. Your child should always have a source of sugar such as orange juice, glucose gel, candy, or milk available in case symptoms of low blood sugar happen. For severe low blood sugar, if your child is not responsive and cannot drink sugar-containing fluids, you should get emergency medical help for your child right away.

  • Allergic reactions are a serious but common side effect of INCRELEX®. Call your child’s doctor right away if your child gets a rash or hives, which generally appear minutes to hours after the injection and may sometimes occur at many places on the skin. Stop taking INCRELEX® and get medical help right away if your child has trouble breathing or goes into shock, with symptoms like dizziness, pale, clammy skin or passing out. INCRELEX® can also cause reactions at the injection site including: loss of fat (lipoatrophy); increase of fat (lipohypertrophy); pain; redness; or bruising.

  • Increased pressure in the brain (intracranial hypertension). INCRELEX®, like growth hormone, can sometimes cause a temporary increase in pressure within the brain. Symptoms include persistent headache and nausea with vomiting.

  • Enlarged tonsils. Signs include: snoring, difficulty breathing, sleep apnea (a condition where breathing stops briefly during sleep), or fluid in the middle-ear.

  • A bone problem called slipped capital femoral epiphysis. When the top of the upper leg bone (femur) slips apart. Get medical help for your child right away if your child develops a limp or has hip or knee pain.

  • Worsened scoliosis (caused by rapid growth).

  • Tumor Growths. Several cases of cancerous tumors have been observed in children who received INCRELEX®. Tell your doctor immediately if your child develops any new growths or symptoms of cancer.

  • Benzyl alcohol toxicity. Benzyl alcohol, a preservative in INCRELEX®, can cause serious side effects, including death in infants.

The most common side effects of INCRELEX® include:

Low blood sugar (hypoglycemia); injection site reactions; allergic reactions; and enlarged tonsils.

These are not all the side effects of INCRELEX®. Call your child’s doctor if your child has side effects that are bothersome or that do not go away. You may report side effects to FDA at 1-800-FDA-1088.

What is INCRELEX®?

INCRELEX® (mecasermin) is a prescription medicine used to treat children who are very short for their age because their bodies do not make enough insulin-like growth factor-1 (IGF-1). This condition is called Severe Primary IGF-1 Deficiency. INCRELEX® should not be used instead of growth hormone. It is not known if INCRELEX® is safe and effective in children under 2 years of age.