1. Biotinidase deficiency: clinical presentation, treatment and screening
Ferenc Papp
University of Szeged, Department of Pediatrics

2. Biotinidase deficiency
Inherited disorder of biotin metabolism
The body cannot recycle endogenous biotin and develop a secondary biotin deficiency

3. Biotin Water-soluble essential B-complex vitamin (vitamin H)
Cofactor for all 4 carboxylase enzymes:
pyruvate caboxylase (gluconeogenesis)
acetyl-CoA carboxylase (fatty acid synthesis)
propionyl-CoA carboxylase (Ile, Val, Met, Thr catabolism)
methylcrotonyl-CoA carboxylase (Leu catabolism)
Dietary biotin is bound to proteins
Free biotin is generated in the intestine by digestive enzymes, by bacteria and by biotinidase

4. Biotin cycle Dietary biotin protein-bound Proteolytic enzymes Bacteria
Biotinidase
Multiple carboxylase deficiency
Infantile/early form
Multiple carboxylase deficiency
Juvenile/late form
Free biotin
Holocarboxylase synthase
Lysine
Biotinidase
Biotin
cycle
Apocarboxylases
Biocytin
Pyruvate
Acetyl-CoA
Propionyl-CoA
Methylcrotonyl-CoA
Apocarboxylases
Proteolytic degradation
Biotin
Holocarboxylases
Protein catabolism
Fatty acid synthesis
Gluconeogenesis

5. Biotinidase deficiency
Two types:
Profound
< 10% of mean normal enzymatic activity
Partial
10-30% reduced activity

6. Epidemiology
Incidence of profound and partial deficiency is 1: in most countries
Brazil 1:9.000
Relatively common in Hungary
estimated combined incidence is 1:23.000
58 children had decreased biotinidase activity from newborns ( , László et al., 2002)
clinical, biochemical and genetic characterization of 20 pts (11 profound, 7 partial, 2 heterozygous)

7. Genetic background Autosomal recessive inheritance
BTD gene 3p25, 4 exons
> 140 disease-causing mutations
Spectrum and frequency of mutations are considerably variable in different ethnic groups
5 mutations are very common in Caucasians: p.D444H, p.Q456H, p.R538C, p.A171T:D444H, c.98:d7i3

8. Genetic background
p.D444H mutation causes 50% reduction in enzyme activity and is almost always associated with partial deficiency
In partial form p.D444H is combined with a severe mutation  10 to 30% enzyme activity
Patients with complete deficiency have two severe mutations  less than 10% enzyme activity

9. Clinical presentation
There is considerable variability of clinical features as well as age of onset of symptoms in enzyme-deficient children
Symptoms may appear from several months to several years of age but may develop as early as 1 week of age (term late form does not apply to all cases!)
First clinical symptoms appear between 3-6 months of age in most of the cases
Symptoms can be seen mostly, but not only in profound form and in pts without treatment

10. Clinical presentaion Skin manifestations Neurological symptoms
Hearing loss, eye problems
Immunodeficiency (fungal and bacterial infections)
Gastrointestinal problems (nausea, vomiting, anorexia)
Metabolic decompensation with acidosis and organic aciduria

11. Cutaneous findings Dry skin Seborrheic dermatitis Ekzema Rashes
Fine and brittle hair
Hair loss or total alopecia
Fungal skin infections

12. Neurological symptoms
Hypotonia
Ataxia
Lethargy
Myoclonic seizures
Developmental delay
Mental retardation
Hearing loss
Visual problems

13. Age of onset: 1 to 180 months (mean 11.8)
Clinical data of 37 symptomatic pts with profound biotinidase deficiency were analysed (Pomponio et al., USA, Ped Res, 1997)
Symptoms
No. of pts
(total 37) %
Rash 25 67
Hypotonia
Seizures 23 62
Hearing deficits
Lethargy 22 59
Alopecia
Ataxia 18 48
Visual problems 14 38
Mental retardation 11 30
Gastrointestinal 8 21
Fungal skin infection 5 13
Age of onset: 1 to 180 months (mean 11.8)
Symptoms improved or resolved after therapy and the children have remained asymptomatic while taking biotin
In some pts the residual neurologic damage has continued

14. Laboratory findings
Metabolic acidosis, ketosis, hyperammonaemia
Elevated C3 and C5OH detected by MS/MS
Pathological organic acid profile in the urine (propionic acid, methylcitrate, 3-methylcrotonic-, 3-hydroxyisovaleric acid, 3-methylcrotonylglycine)
These lab findings can be observed mostly in untreated pts or in metabolic decompensation

15. Diagnosis
Based on detection of decreased biotinidase activity in the blood and/or in the serum compared to a normal control by using colorimetric test
DNA testing is also available, but this is not necessary for confirmation of biotinidase deficiency

16. Treatment
Pharmacologic dose of biotin resolves many of the clinical features in symptomatic pts and prevents the development of symptoms in asymptomatic pts
Recommended daily dose is 5-20 mg orally
Lifelong treatment is needed (carriers do not need therapy)
Hearing loss, eye problems and developmental delay do not resolve completely with biotin therapy
Early diagnosis and treatment are needed before permanent neurologic damage occurs

17. Screening
A colorimetric method for diagnosing of biotinidase deficiency was developed by Knappe (1963)
It was adopted for newborn screening by Heard (1984)
In Hungary screening was introduced in 1989
Biotinidase deficiency has been screened in 47 of 51 states of the USA and in 6 European countries (Sweden, Germany, Switzerland, Austria, Lichtenstein and Hungary) at 2007
Screening has been started in 4 more European countries with pilot studies at the same time (Spain, Belgium, Italy, Turkey)

18. Screening method A quantitative colorimetric method is used
Enzyme activity is measured directly in the DBS
Result is not influenced by days of life, gestational age or breast feeding
Only transfusion of a newborn can interfere with biotinidase screening, in that case screening needs to be repeated at the age of 2 weeks and 60 days

19. Summary Inherited disorder of biotin recycling
Two severity forms: profound and partial
If left untreated affected individuals develop severe clinical abnormalities
In symptomatic pts mostly neurologic and cutaneous complications can be observed
It can be treated effectively with biotin supplementation

20. Summary Permanent neurologic symptoms do not resolve with therapy
Early diagnosis is very important, so that therapy can be initiated before clinical symptoms appear
Clinical consequencies of biotinidase deficiency can be minimized effectively by newborn screening