Isobutyrylglycinuria (IBG) is an inherited condition in which the body is unable to break down certain proteins. It is classified as an organic acid condition because IBG can lead to a harmful amount of organic acids and other toxins in the body. Symptoms of the condition vary. If IBG is identified early and treatment is begun, individuals with the condition may be able to lead healthy lives.
Organic Acid Conditions
Isobutyrylglycinuria (IBG) is a rare condition. The exact number of children affected by IBG is unknown. Fewer than 30 cases have been reported, and most of the people identified as having IBG did not have any health effects from the condition.
Also known as
- IBD deficiency
- Isobutyryl-CoA dehydrogenase deficiency
- Isobutyryl-coenzyme A dehydrogenase deficiency
- Acyl-CoA dehydrogenase family – member 8
- ACAD8 deficiency
Your baby’s doctor may ask you if your baby is showing any of the signs of IBG (see Early Signs below). If your baby has certain signs, your baby’s doctor may suggest starting immediate treatment.
If your baby’s newborn screening result for isobutyrylglycinuria (IBG) was out of the normal range, your baby’s doctor or the state screening program will contact you to arrange for your baby to have additional testing. It is important to remember that an out-of-range screening result does not necessarily mean that your child has the condition. An out-of-range result may occur because the initial blood sample was too small or the test was performed too early. However, a few babies do have the condition, so it is very important that you go to your follow-up appointment for a confirmatory test. Because the harmful effects of untreated IBG can occur soon after birth, follow-up testing must be completed as soon as possible to determine whether or not your baby has the condition.
Follow-up testing may involve checking your baby’s urine and blood samples for harmful amounts of acids and toxins. Certain acids and toxins build up in the body when a child has an organic acid condition, so measuring the amounts of these substances in your baby’s body can help doctors determine if your baby has a condition. A high amount of C4 acylcarnitine in the blood and urine and a high amount of organic acids in the urine might be a sign that your baby has IBG. In some cases, follow-up testing may also include testing a very small sample of skin.
Isobutyrylglycinuria (IBG) is a very rare condition. Signs of IBG have only ever been reported in one case. This child’s signs began at age one.
Signs of IBG include:
- Delayed growth
- Sleeping longer or more often
- Pale skin
- Trouble regulating body temperature (your baby may get cold easily)
- Difficulty breathing
Many of these signs may occur when your baby eats foods that they body cannot break down. They can be triggered by long periods of time without eating, illnesses, and infections.
If your baby shows any of these signs, be sure to contact your baby’s doctor immediately.
Your baby will probably need to follow a restricted diet in order to avoid eating proteins that their body cannot break down. A nutritionist or a dietician can help you plan your baby’s diet.
Your baby’s doctor might also recommend special formulas and foods for children with isobutyrylglycinura (IBG). These formulas will likely need to continue through adulthood.
Your baby will also need to eat often in order to avoid many of the signs mentioned in the Early Signs section.
Supplements and Medications
Your baby may need to take prescription L-carnitine supplements. L-carnitine is a substance that is naturally produced in the body, but your baby’s body might not make enough of it. These supplements help to break down fats and get rid of harmful waste substances that build up in the body. Your baby’s doctor will need to write a prescription for these supplements.
L-carnitine supplements can also help prevent or reverse some of the more severe health complications associated with IBG mentioned in the Expected Outcomes section.
We do not yet know how effective treatments for isobutyrylglycinuria (IBG) are. With early and ongoing treatment, your child will likely have healthy growth and development. This is why newborn screening is so important.
Children who do not receive treatment for IBG are at risk for more severe health complications, including a low red blood cell count (called anemia) and an enlarged, weak heart (known as cardiomyopathy). L-carnitine treatments can help prevent, and even reverse, anemia and heart trouble that may develop.
When we eat food, enzymes help break it down. Certain enzymes break down proteins into their building blocks, called amino acids. Other enzymes help break down those amino acids. In isobutyrylglycinuria (IBG), the enzyme isobutyryl-CoA dehydrogenase is not working correctly.
This enzyme’s job is to help break down the amino acid valine. Babies with IBG either do not make enough or make non-working isobutyryl-CoA dehydrogenase. When this enzyme does not work correctly, the body cannot break down valine. If your baby’s body cannot break down valine, high acid levels build up in the body. Everyone has some acid in their blood, but high levels can be toxic.
IBG is an autosomal recessive genetic condition. This means that a child must inherit two copies of the non-working gene for IBG, one from each parent, in order to have the condition. The parents of a child with an autosomal recessive condition each carry one copy of the non-working gene, but they typically do not show signs and symptoms of the condition. While having a child with IBG is rare, when both parents are carriers, they can have more than one child with the condition. Learn more about autosomal recessive inheritance.
Support for Isobutyrylglycinuria
Support groups can help connect families who have a child or other family member affected by isobutyrylglycinuria (IBG) with a supportive community of people who have experience and expertise in living with the condition. These organizations offer resources for families, affected individuals, health care providers, and advocates.
Work with your baby’s doctor to determine the next steps for your baby’s care. Some children with isobutyrylglycinuria (IBG) have severe signs and symptoms while others may never develop them at all. The type of care your child needs depends on whether they develop signs and symptoms. Your baby’s doctor may work with a metabolic specialist and a dietician to provide care for your baby. Some children with IBG have developmental delays. If you think that your baby is not meeting their developmental milestones, ask your baby's health care provider about the next steps in accessing a developmental evaluation and care.
Because IBG is a genetic condition, you may want to talk with a genetics specialist. A genetic counselor or geneticist can help you understand the causes of the condition, discuss genetic testing for IBG, and understand what this diagnosis means for other family members and future pregnancies. Speak with your baby’s doctor about getting a referral. The Clinic Services Search Engine offered by the American College of Medical Genetics and Genomics (ACMG) and the Find a Genetic Counselor tool on the National Society of Genetic Counselors (NSGC) website are two good resources for you or your baby's health care provider to use to identify local specialists.
At this time we have not located a family story for this particular condition. If your family is affected by isobutyrylglycinuria (IBG) and you would like to share your story, please contact us so other families may learn from your experience.
Each family's experience with a condition is unique, but there are some parts of the evaluation and treatment of IBG that are similar to other organic acid conditions. You may find it useful to read the stories of families affected by other organic acid conditions. You can read these stories at the Organic Acidemia Association's website.