Here is some information about the metabolic disorder my son was born with. This is an uncommon genetic metabolic disorder and many doctors aren't familiar with it or even heard of it before. My hope is that this information can and will help other parents who may have children with this disorder. Please pass this info on to friends, family and physicians.
My son was diagnosed with Biotinidase Deficiency through a routine newborn screening test. It is important to note that not all states test for BTD in their routine newborn screening. The state of Maine had just added the test for BTD two months before my son was born (1999). He was the first baby in Maine to be diagnosed with BTD through routine newborn screening. He has been on 10mg biotin since 6wks of age and will be for the rest of his life.
If you have any questions please feel free to ask me...
A Booklet for Families & Professionals By Deborah L. Thibodeau, M.S. and Barry Wolf, MD., Ph.D.
You may have taken home a healthy newborn baby from the hospital, and now the doctors are telling you that there is something wrong. You may feel shocked, sad, frightened, or angry. You may ask, "How could this be?"
Or maybe you have an older child. You have known for some time that something is not quite right. Just now, doctors have diagnosed your child's condition. You may feel relieved that a diagnosis has finally been made, but afraid of what the diagnosis means.
Regardless of your child's age at the time of the diagnosis, being told that your child has biotinidase deficiency was probably confusing and scary because you had never heard of this condition before. You probably wondered what this diagnosis would mean for your child and your family.
Your doctor or a genetic counselor has explained to you that biotinidase deficiency is a treatable genetic condition. You have been given a lot of new information at a time when your mind has been preoccupied with the health of your child. You may still have many questions about your child's health.
This booklet has been written to answer many of the questions that families have concerning biotinidase deficiency. We hope that it will serve as a resource for you and others who wish to learn more about your child's condition. We have included listings of resources to which you can turn for more information or assistance. Finally, we hope that this booklet will help you realize that you are not alone in raising a child with biotinidase deficiency.
Although this book was prepared for families, it was also written to introduce medical professionals to biotinidase deficiency. A list of references is provided should you desire more detailed information from the medical literature.
WHAT IS BIOTINIDASE DEFICIENCY?
Biotinidase deficiency is a treatable, inherited metabolic disorder in which the body cannot process the vitamin biotin in a normal manner.
Metabolic processes occur within the body.
The human body is very complex. Inside of our bodies, thousands of chemical reactions occur involving the foods we eat, the air we breathe, how we sense the environment, and how we develop and grow. Some of these chemical reactions allow substances like foods to be processed or metabolized so that they can be used by the body.
Enzymes carry out metabolic processes.
Enzymes are special proteins made by the body that allow chemical reactions to occur. Enzymes that work properly are said to be active or to have activity. Some enzymes need vitamins in order to be active. Often, the activity of a single enzyme may be required to make several different substances that the body needs.
Sometimes the body does not make enough of a particular enzyme or the enzyme that is made does not work properly. This causes the enzyme to have decreased activity and it cannot carry out its normal work load. Other chemical reactions that rely on that enzyme may also be slowed down or interrupted.
If the enzyme activity is less than 10% of normal activity, it is usually considered to be deficient. Enzyme deficiencies often lead to medical problems. Medical conditions resulting from enzyme deficiencies are called metabolic disorders because the metabolic or chemical processes within the body are not occurring normally.
Biotinidase is an enzyme that sometimes has decreased activity.
Biotinidase is an important enzyme in the body. People with biotinidase deficiency do not have enough biotinidase activity. An individual with biotinidase deficiency usually has enzyme activity that is less than 10% of normal and sometimes there is almost no activity at all. Individuals with less than 10% of normal biotinidase activity are considered to have profound biotinidase deficiency. The parents of children with biotinidase deficiency have approximately 50% of normal biotinidase activity which is usually enough activity to prevent medical problems. People classified as having partial biotinidase deficiency have intermediate levels of biotinidase activity, 10-30% of normal.
Active biotinidase is needed for the body to process dietary biotin.
Biotinidase is an important enzyme in the biotin cycle, the chain of chemical reactions involved in the use and reuse of the vitamin biotin. One important role of biotinidase is to separate or free biotin from proteins to which it is bound in foods. Biotin in its free form can then be used by the body. Additionally, biotinidase lets the body recycle or reuse the biotin over and over again so that we do not need to consume large amounts of this vitamin in our diets.
Biotin is an important vitamin.
Free biotin is required to allow a group of enzymes called carboxylases to function properly. Carboxylases are important in the production of certain fats and carbohydrates and for the breakdown of proteins. In order for inactive carboxylases to become active, free biotin must be attached to the amino acid, lysine, at a special site on the inactive carboxylases. Eventually, the carboxylases are broken down, but the biotin stays attached to lysine. This biotin-lysine complex is known as biocytin. Biocytin is normally broken down by biotinidase into free biotin and lysine. In this way, biotin is recycled and can be reused by the carboxylases.
Biotinidase deficiency interrupts the biotin cycle.
When biotinidase activity is deficient, protein-bound biotin in the diet cannot be used by carboxylases. The carboxylases are unable to perform their normal functions, altering fat, carbohydrate and protein metabolism. This causes harmful by-products to collect in the body. Without adequate biotinidase activity, the body needs large amounts of free biotin, more than is supplied by the normal diet. When this is not available, health problems usually result.
HOW WILL BIOTINIDASE DEFICIENCY AFFECT MY CHILD?
Without biotin therapy, children with biotinidase deficiency may develop one or more of the symptoms as shown...
>50% of affected children
Alopecia (hair loss)
Hypotonia (poor muscle tone)
Skin rash/skin infection
25-50% of affected children
Ataxia (poor coordination)
Conjunctivitis (redness of the eye)
10-25% of affected children
<10% of affected children
Hepatomegaly (enlarged liver)
Splenomegaly (enlarged spleen)
Symptoms usually appear between three to six months of age, but may appear as early as one week of age or as late as ten years of age. The number of symptoms that a child develops and the severity of the disorder vary from child to child, even within the same family.
Early symptoms of biotinidase deficiency often include seizures of various types, particularly myoclonic seizures, and hypotonia (poor muscle tone). These symptoms are not specific to biotinidase deficiency, therefore, a diagnosis is not usually made immediately. Other early symptoms include breathing problems, such as tachypnea (fast breathing), hyperventilation (fast, shallow breathing), stridor (difficulty moving air through the windpipe), and apnea (long pauses in breathing); skin rashes often called seborrheic or atopic dermatitis; partial or complete alopecia (hair loss); and conjunctivitis (redness of the eye). Ataxia (poor coordination or clumsiness) and developmental delay usually occur later. The immune system also appears to be altered, and fungal and bacterial infections can occur in untreated children. Hearing loss is usually sensorineural (involves the nerve to the ear) and a variety of eye problems, especially optic atrophy (small optic disk that can cause loss of vision), may develop. Abnormal substances often accumulate in the urine (organic aciduria) and in the blood (ketolactic acidosis and hyperammonemia).. These biochemical abnormalities may cause damage to important organs like the brain, skin, inner ear, and eyes and may be life threatening.
Some untreated infants and children have died from this disorder.
Unrecognized and untreated biotinidase deficiency has also been considered as one possible cause of sudden infant death syndrome (SIDS), although more information is needed in this area. If you have experienced such a loss, you may wish to discuss it again with your doctor. A careful review of your baby's medical records may provide evidence that your baby had experienced symptoms of unrecognized biotinidase deficiency.
All children who have developed symptoms of biotinidase deficiency have improved when treated with recommended doses of biotin. The biochemical abnormalities, seizures, muscle tone, and skin rash usually show rapid improvement. Hair begins to grow back over a period of weeks to months. Other symptoms including hearing loss, visual impairments, and developmental delay are not always corrected by treatment, but they usually do not get worse. This may be because organs are damaged prior to treatment or possibly because high levels of substances such as biocytin are present even after treatment has begun. With proper treatment, biotinidase deficiency is not a life threatening condition.
WHAT IS PARTIAL BIOTINIDASE DEFICIENCY?
Biotinidase deficiency can appear in a milder form called partial biotinidase deficiency. In partial biotinidase deficiency, the activity of biotinidase is about 10-30% of normal compared to less than 10% in the profound or more serious form of this condition. Thus far, all of the children who have been classified as having partial biotinidase deficiency have been identified through newborn screening programs. Untreated children with partial deficiency are usually healthy, although symptoms have occurred in some children when they are stressed from an infection or poor diet. Currently, most children with this partial biotinidase deficiency are being treated with prescribed doses of biotin, usually slightly less (2 to 5 mg/day) than that used to treat profound deficiency, whereas others remain untreated and are carefully watched for the development of symptoms. The full clinical significance of partial deficiency is still not known with certainty.
HOW IS BIOTINIDASE DEFICIENCY TREATED?
People with biotinidase deficiency are unable to use naturally occurring biotin in their diets and are unable to recycle biotin. For successful treatment, they require free or unbound biotin supplements. The recommended dose of free biotin is 5-20 milligrams (mg) per day taken orally, which provides the body with the free biotin it needs. These large doses are 10 to 20 times more than the Recommended Dietary Allowance (RDA).
As discussed earlier, all children with biotinidase deficiency who have developed symptoms have improved following biotin treatment. Children with biotinidase deficiency who are carefully treated before symptoms occur rarely, if ever, develop any symptoms related to the disorder.
WHERE DO WE GET BIOTIN?
Your child's doctor must prescribe large doses of free biotin to treat your child. Diets containing egg yolks, liver, and certain vegetables are "rich" in biotin, but they are usually not effective in treating this condition because the biotin is protein-bound, not in a free form.
It is often difficult to obtain free biotin in adequate dosages from local pharmacies or health food stores. Your doctor can arrange to have the biotin purchased from a hospital pharmacy or pharmaceutical company that can supply the biotin in a form that your child can use.
Biotin is in the form of a crystal and is usually supplied by pharmacists in a capsule or tablet. The capsules can be opened or the tablets can be crushed to add the biotin to a baby's milk or a child's food. Biotin supplied in solution should not be used because the biotin often settles out of the liquid, possibly resulting in inappropriate doses. In addition, these solutions may be prone to grow bacteria. The biotin is usually given once a day, such as first thing in the morning, or may be divided into two doses each day, in the morning and in the evening.
The cost of biotin treatment varies, but is generally between 30 and 90 cents per capsule (5 or 10 mg) or between $100 to $350 per year. Unfortunately, some insurance companies do not cover the cost of prescriptions for vitamins including biotin. If you have had this problem with your health insurance carrier, you may wish to contact the company directly or ask your doctor to write a letter explaining the importance of biotin treatment for your child.
BIOTINIDASE DEFICIENCY REQUIRES LIFELONG BIOTIN THERAPY.
Our bodies need biotin throughout life, therefore, biotin therapy begins following the diagnosis and continues for life. No serious side effects of biotin treatment are known, although little information is available on the long term effects of biotin treatment. We do not expect that adults treated for biotinidase deficiency will have any new health problems from the disease or from the treatment. Treated biotinidase deficiency is not expected to pose a risk to mothers or their developing babies. However, because we do not yet have experience with pregnancies in women with biotinidase deficiency, research is needed in this area. Life expectancy for people with biotinidase deficiency is anticipated to be normal with proper treatment.
By following the progress of children treated for biotinidase deficiency, doctors are gaining a better understanding of the body's need for biotin.
WHAT IF WE MISS A DAY OF TREATMENT?
Missing a dose of biotin once in a while probably will not harm your child; however, not making an effort to follow the prescribed treatment may cause your child to develop symptoms of biotinidase deficiency. If at any time your child develops any of the symptoms of biotinidase deficiency, you should have the child examined by his or her doctor to determine if the dose of biotin needs to be changed.
HOW IS BIOTINIDASE DEFICIENCY DETECTED?
There are three ways doctors may suspect a diagnosis of biotinidase deficiency. An infant may be identified by newborn screening before symptoms develop, an infant or child may develop symptoms that lead to the diagnosis, or if there has been a previous affected child in the family, the diagnosis can be made prenatally. Prenatal diagnosis is discussed in a later section. Doctors then confirm the diagnosis of biotinidase deficiency by measuring the activity of biotinidase in serum.
All 50 states in the United States and many other countries have newborn screening programs. Through these programs, all babies born within the state or country are tested for specific disorders such as phenylketonuria (PKU) and hypothyroidism. Early diagnosis of these conditions allows doctors to treat babies before they become sick.
Newborn screening for biotinidase deficiency began in Virginia in 1984 and is now performed in many other states and countries. Not all screening programs include testing for biotinidase deficiency. Currently, about one half of the states and provinces in the U.S. and Canada screen for this condition. In addition, many countries are also screening all or some of their newborns for biotinidase deficiency.
How was my baby screened?
The heels of infants are pricked soon after birth, usually just before they go home from the hospital. The blood is spotted on filter paper cards, dried, and sent to a newborn screening laboratory for testing. The dried blood from just one card can be used to screen a baby for several different diseases. To screen for biotinidase deficiency, the activity of biotinidase in the dried blood is measured. Abnormal test results are repeated and confirmed by measuring biotinidase activity in serum or plasma of a fresh blood sample. Usually the cost of testing is paid by the newborn screening program, and parents often do not even realize that their baby was screened unless the results are abnormal.
If your child was detected through newborn screening, the diagnosis was made quickly, probably before any symptoms developed.
If your child was not screened for biotinidase deficiency at birth, your child was probably diagnosed after some of the clinical symptoms of biotinidase deficiency appeared. Children diagnosed in this way may have had medical problems for some time before doctors suspected the correct cause. Some children are even diagnosed as having other disorders because many of the symptoms of biotinidase deficiency can resemble those produced by other conditions. But once biotinidase deficiency is suspected, a blood sample is sent to a laboratory to measure the activity of biotinidase. Fortunately, once the correct diagnosis is made, most of the symptoms improve or disappear with treatment.
HOW COMMON IS BIOTINIDASE DEFICIENCY?
Biotinidase deficiency is very rare.
Biotinidase deficiency is a rare metabolic disorder. Only about 1 in 60,000 babies is born with profound or partial biotinidase deficiency. Although you may feel very alone having a child with biotinidase deficiency, there are many other families who share your concerns. Worldwide, more than 150 children have been diagnosed with this condition because they developed symptoms, and more than 300 children have been diagnosed by newborn screening.
Biotinidase deficiency is a genetic condition.
Children with biotinidase deficiency have inherited two copies of the gene for biotinidase deficiency, one from each parent. Biotinidase deficiency is not caused by anything the parents did or did not do before or after a child was born.
Genes are units of genetic information.
The body's instructions for making the enzyme biotinidase are encoded in a pair of genes. Genes are tiny units of genetic information that tell the cells of our body to make certain products such as enzymes. We all have a unique set of 50,000-100,000 different genes, each coding for specific products or traits. The instructions are read from a unique code in the DNA, the material from which genes are made. If the instructions have an error in them, the gene product will not work properly.
Genes are packaged on the chromosomes.
Genes are organized into small thread-like packages called chromosomes, each of which contains about 2,000-5,000 genes. Each cell has 23 pairs of chromosomes, one member of each chromosome pair is inherited from each parent. There are 22 pairs of autosomes (non-sex chromosomes), and 1 pair of sex chromosomes (chromosomes that determine if a person is male or female).
Genes come in pairs, one from each parent.
Since chromosomes come in pairs, genes also come in pairs. One copy of each gene is inherited from one's mother and the other copy of each gene is inherited from one's father. Therefore, children share half of their genes with each parent, but also differ because of the genes received from the other parent. Brothers and sisters also share half of their genes, on the average, but they never inherit the exact same combination of genes unless they are identical twins.
Biotinidase deficiency is caused by having a pair of defective genes.
People with biotinidase deficiency receive a defective biotinidase gene from both of their parents. Since they do not have even one copy of the gene that codes for normal, active biotinidase, the activity of biotinidase in their bodies is very low or undetectable.
HOW IS BIOTINIDASE DEFICIENCY INHERITED?
Biotinidase Deficiency is an autosomal recessive condition.
Biotinidase deficiency is inherited as an autosomal recessive trait. This means that the gene is on an autosome rather than a sex chromosome, and that the trait or disorder, is only expressed when an individual has two "doses" of the abnormal gene, one inherited from each parent.
People who have one gene for biotinidase deficiency and one normal gene show half normal enzyme activity levels, but are healthy because half normal levels are sufficient to prevent any symptoms. Individuals who have a single abnormal gene for biotinidase deficiency (i.e., the parents of affected children) are said to be "carriers" (also called heterozygotes) of biotinidase deficiency.
Parents of affected children must be carriers.
We are all carriers of genes for recessive genetic conditions. These genes go unnoticed unless both parents happen to be carriers of the same abnormal gene and then have a child who inherits two "doses" of the recessive gene and is affected with the condition.
Children with biotinidase deficiency inherit one copy of the gene for biotinidase deficiency from each parent. Both parents must therefore be carriers in order to have a child with biotinidase deficiency.
Carrier parents can have more than one affected child.
We all pass on one copy of each gene pair to our children. A person who carries the gene for biotinidase deficiency therefore has a 1 in 2 or 50% chance with each pregnancy of passing on the gene for biotinidase deficiency. They also have a 50% chance of passing on the normal or functional gene.
For a child to be affected, both parents must carry a gene for biotinidase deficiency, and both parents must pass on that gene. This means that for each pregnancy, carrier parents have a 1 in 4 or 25% chance of having an affected child. They also have a 25% chance of both passing on the normal gene and having an unaffected child. Finally, there is a 50% chance that a child will inherit the recessive gene from one parent and the normal gene from the other. These children will be carriers, just like the parents.
Should our other children be tested?
All of your other children should be tested for biotinidase deficiency even if they have do not have symptoms of the condition. This will identify children who are only mildly affected or have not yet developed symptoms. Biotin treatment can then be started. Testing can also identify carriers of biotinidase deficiency, and this information my be useful to your children when they grow up and are planning their own families.
What can be done in future pregnancies?
Babies that have biotinidase deficiency do not develop medical problems from the disease until after they are born. Carrier mothers apparently supply the developing baby (fetus) with enough free biotin to prevent symptoms from appearing. Therefore, although it is possible, prenatal treatment for this condition is usually not considered necessary. Some doctors recommend that women at risk for having an affected child take prenatal vitamins containing some biotin (many prenatal vitamin preparations do not contain biotin) to ensure adequate biotin for the baby.
It is possible to determine if a baby has biotinidase deficiency during a pregnancy by withdrawing a sample of amniotic fluid and measuring the activity of biotinidase in cells grown from the fluid. Amniotic fluid is the fluid or "water" inside of the womb that surrounds the baby. Amniocentesis is the procedure used to withdraw the fluid using a needle inserted into the uterus. Amniocentesis is usually performed between the 15th and 17th week of the pregnancy and is routinely offered to pregnant women for prenatal diagnosis of other genetic conditions. There is a risk of having a pregnancy complication caused by this procedure, therefore families must carefully weigh the risks and benefits of early diagnosis before deciding to have amniocentesis. These issues may be discussed with your doctor or genetic counselor.
Chorionic villus sampling (CVS) is another method of prenatal testing for various genetic conditions. Since biotinidase activity has not been measured in chorionic villus samples, it is not known if prenatal diagnosis by this method is possible. Regardless of whether you have prenatal diagnosis, it is important for babies who are at risk of inheriting this condition to be tested shortly after birth so that affected children can be identified and treated.
Will our grandchildren have biotinidase deficiency?
Since individuals with biotinidase deficiency have two copies of the gene for biotinidase deficiency, all of their children will inherit one copy of the gene. But in order to have a child with biotinidase deficiency, their partners must also be carriers and pass on the gene for biotinidase deficiency. Only about 1 in 125 people carry the gene for biotinidase deficiency; therefore, the chance that your grandchildren will have biotinidase deficiency is about 1 in 500, but carrier testing for biotinidase deficiency can more accurately determine their risk. All of your children who have biotinidase deficiency or are carriers of the gene may wish to see a genetic counselor to discuss risks and available testing when they begin to plan their own families.
Should we discuss testing with other relatives?
Your child's aunts, uncles, cousins, and other distant relatives may also carry the gene for biotinidase deficiency. You may wish to tell other family members that biotinidase deficiency is a genetic condition. If they would like to be tested, they can discuss it with their doctors or arrange to see a genetic counselor.
WHAT CAN I EXPECT FROM MY CHILD?
Infants who are diagnosed with biotinidase deficiency and treated before symptoms appear are not expected to develop health problems from this condition. Parents tell us that these children are just like other children except that they require a daily dose of prescribed biotin and regular medical checkups.
Children who begin biotin therapy after symptoms appear usually show rapid improvement, although some effects of the condition may persist such as hearing loss, visual impairments, and developmental delay. Your child's unique response to biotin treatment can best be addressed by your child's doctor. Your doctor or genetic counselor can also help your family locate community resources if your child has special needs.
Biotinidase deficiency was first described in 1983. Since then, doctors and scientists have learned much about this genetic condition. But there are still many unanswered questions. For example, why does reduced biotinidase activity lead to hair loss, hearing problems, and seizures? Is there any way to completely correct all health problems caused by biotinidase deficiency if the diagnosis is made late? Is biotin therapy the best treatment? Is the biocytin that is produced in individuals with biotinidase deficiency harmful? Does biotin therapy cause increased amounts of biocytin to be made? Now that we can determine the specific mutation in the biotinidase gene that causes biotinidase deficiency, are there certain mutations that are more likely result in producing symptoms in untreated individuals than others? Researchers are currently trying to answer these and other questions so that your child can receive the most effective treatment possible and so that we can provide you with complete and accurate information.
Recently, the gene for human biotinidase has been isolated and characterized. The biotinidase gene has been shown to be located on the tip of the short arm of chromosome 3. Our laboratory has found over forty different mutations that cause biotinidase deficiency. It is possible to determine the mutation(s) in your child's DNA that caused biotinidase deficiency. Our laboratory is conducting mutation analysis on DNA from children with profound and partial biotinidase deficiency from around the world.
We are in the process of determining the mutations in the DNA that cause profound and partial biotinidase deficiency in children who were symptomatic at the time of diagnosis or who were found to have the deficiency by newborn screening. We would now like to determine the mutation or mutations that causes biotinidase deficiency in your child. This will allow us to compare the mutations in symptomatic children and compare them to the mutations of children identified by newborn screening. This may help us determine if there are differences in the groups and if it is of clinical importance. To do this study we must obtain blood samples from the child with biotinidase deficiency and, if possible from both parents. This testing is experimental at this time.
WHERE CAN WE GET HELP?
Doctors and Genetic Counselors
You may have many questions concerning your child's health, and many of these questions can be answered by your family doctor or pediatrician. Your doctor may also refer your child to a biochemical, metabolic, or genetic specialist who will be able to answer more of your questions. For detailed information about the genetics of biotinidase deficiency, you may wish to see a genetic counselor who can discuss with you the chances that other family members will have biotinidase deficiency. A genetic counselor can also tell you about resources in the community that may assist you and your child.
Being the parent of a child with a rare genetic condition can be a frightening and lonely experience. You may not know any other families who share your hopes and fears concerning biotinidase deficiency. Parents sometimes find it helpful to speak to other families to hear how other children are doing or just to know that they are not alone. Your doctor or genetic counselor may be able to help you contact another family who has a child with biotinidase deficiency.. Some organizations such as Parent to Parent and the National Organization for Rare Disorders (NORD), listed below, also offer this service.
The following organizations may provide additional assistance:
In the U..S.
National Organization for Rare Disorders (NORD)
P.O. Box 8923
New Fairfield, CT 06812-1783
March of Dimes Birth Defects Foundation
1275 Mamaroneck Avenue
White Plains, NY 10605
Parent to Parent National Survey Project
The Beach Center on Families and Disabilities
University of Kansas
3111 Hayworth Hall
Lawrence, KS 66045
The Canadian Society for Metabolic Disease (CSMD)
5301 Ranger Ave.
North Vancouver, BC V7R 3M7
POINTS TO REMEMBER
Biotinidase deficiency is a rare, treatable, genetic condition in which the body cannot use dietary biotin.
Infants may be identified by newborn screening before symptoms develop or a diagnosis may be made in an older infant or child who has been experiencing some of the following problems: seizures, hair loss, skin rash, and developmental delay.
Lifelong treatment with prescribed doses of biotin is very effective in preventing or improving most symptoms.
Parents who have a child with biotinidase deficiency have a 1 in 4 or 25% chance with each pregnancy of having another child with biotinidase deficiency.
Other family members may also carry the gene for biotinidase deficiency.
Carrier testing and prenatal testing is available.
It is possible to determine the mutation(s) in the biotinidase gene of your child that causes biotinidase deficiency (experimental).