What is the Disease B7 Deficiency?
Vitamin B7, more commonly known as biotin, is a water-soluble vitamin essential for several metabolic functions, including the breakdown of fats, carbohydrates, and proteins. A true dietary deficiency is uncommon because biotin is widely available in foods, and gut bacteria can also produce it. The most significant disease related to B7 deficiency is biotinidase deficiency, an inherited genetic disorder. This condition prevents the body from recycling biotin, leading to a functional deficiency even when a person's dietary intake is normal. Biotinidase deficiency is a type of multiple carboxylase deficiency, a group of metabolic disorders that can also include holocarboxylase synthetase deficiency.
The Primary Genetic Cause: Biotinidase Deficiency
Biotinidase deficiency is an autosomal recessive disorder caused by mutations in the BTD gene. The BTD gene provides instructions for creating the biotinidase enzyme, which is responsible for cleaving biotin from proteins in food and from cellular turnover. Without a functional biotinidase enzyme, the body cannot free biotin for use by other enzymes called carboxylases, which are vital for metabolism. This leads to a build-up of potentially toxic compounds and a shortage of free biotin.
- Profound Biotinidase Deficiency: Characterized by less than 10% of normal biotinidase enzyme activity. This form often presents with severe symptoms early in infancy.
- Partial Biotinidase Deficiency: Involves 10-30% of normal enzyme activity. Symptoms may be milder and only appear during periods of stress, such as infection or illness.
Other Forms of Biotin Deficiency
While genetic disorders are the main cause of profound deficiency, several other factors can lead to an acquired biotin deficiency.
- Dietary: Excessive, long-term consumption of raw egg whites can cause deficiency because a protein called avidin binds tightly to biotin, preventing its absorption. Cooking denatures avidin, eliminating this risk.
- Medical Conditions: Certain gastrointestinal conditions like Crohn's disease or inflammatory bowel disease can impair biotin absorption. Prolonged use of total parenteral nutrition (TPN) without sufficient biotin can also cause deficiency.
- Medications: Long-term use of specific anticonvulsants (e.g., phenytoin, primidone, carbamazepine) can interfere with biotin metabolism. Extended courses of oral antibiotics can disrupt gut bacteria that produce biotin.
Symptoms Associated with B7 Deficiency
The symptoms of biotin deficiency are diverse and can affect multiple body systems. The severity and manifestation depend on the cause and degree of the deficiency. Symptoms often appear gradually.
Dermatological and Hair Symptoms
- Thinning hair (alopecia) and eventual hair loss across the body
- A scaly, red rash around body openings (eyes, nose, mouth)
- Unusual fat distribution in the face, sometimes referred to as 'biotin deficiency facies'
- Skin infections, particularly candidiasis
- Brittle nails
Neurological Symptoms
- Seizures
- Lethargy, depression, and hallucinations (in adults)
- Hypotonia (weak muscle tone) and developmental delay (in infants)
- Ataxia (poor coordination or unsteady gait)
- Paresthesias (numbness or tingling in the extremities)
Other Symptoms
- Conjunctivitis (red, inflamed eyes)
- Metabolic issues, such as ketolactic acidosis
- Impaired immune function and increased susceptibility to infections
How to Diagnose Biotin Deficiency
Early diagnosis is critical, especially for inherited metabolic disorders, to prevent irreversible damage.
- Newborn Screening: In many countries, newborn screening programs routinely test for biotinidase deficiency via a heel prick blood sample.
- Blood and Urine Tests: For symptomatic individuals, lab tests measure biotinidase enzyme activity, plasma biotin levels, and levels of certain organic acids in the urine (e.g., 3-hydroxyisovaleric acid).
- Family and Clinical History: A doctor will evaluate symptoms, family history of similar disorders, diet, and medication use to determine the cause of the deficiency.
Treatment and Management for B7 Deficiency
Treatment for biotin deficiency is straightforward and highly effective, consisting of biotin supplementation. The primary treatment approach varies depending on the underlying cause.
- Genetic Disorders: For inherited conditions like biotinidase deficiency, treatment involves lifelong oral biotin supplementation, typically 5 to 20 mg per day. Early treatment can prevent symptoms from developing or reverse many that have already appeared. However, some complications, such as hearing loss and developmental delays, may become permanent if treatment is delayed.
- Acquired Deficiencies: For deficiencies caused by diet, medication, or medical conditions, addressing the root cause is key. This may involve dietary changes, adjusting medication, or providing supplemental biotin temporarily until levels are restored.
- High-Dose Biotin: In some cases, higher doses of biotin may be required, particularly for conditions like holocarboxylase synthetase deficiency.
Genetic vs. Acquired Biotin Deficiency
| Feature | Genetic Biotinidase Deficiency | Acquired Biotin Deficiency |
|---|---|---|
| Cause | Inherited mutation in the BTD gene. | Dietary factors (raw eggs), medications, TPN, alcoholism, or malabsorption disorders. |
| Incidence | Rare, approximately 1 in 60,000 newborns. | Also rare in the general population, but more common in at-risk groups. |
| Age of Onset | Typically appears in infancy, but can manifest later in childhood or adulthood. | Can occur at any age, depending on the cause. |
| Treatment | Lifelong oral biotin supplementation. | Correction of the underlying cause; sometimes temporary supplementation. |
| Reversibility | Symptoms are generally reversible with early treatment, but some neurological damage may be permanent if delayed. | Symptoms typically resolve upon correction of the underlying cause. |
Conclusion
In summary, the name of the disease b7 deficiency most often refers to the genetic disorder biotinidase deficiency, which is a key cause of the metabolic issues seen when biotin is functionally unavailable. While dietary deficiency is rare, it can occur under specific circumstances, such as excessive raw egg white consumption or long-term medication use. Early diagnosis, facilitated by routine newborn screening in many countries, and consistent lifelong treatment with oral biotin are critical for managing biotinidase deficiency and preventing irreversible neurological and cutaneous complications. It is important to consult a healthcare provider for proper diagnosis and treatment if a deficiency is suspected.
For more information on the role of biotin, visit the National Institutes of Health: Biotin - Health Professional Fact Sheet.
