Multiple carboxylase deficiency due to deficiency of biotinidase

Outcomes of oral biotin treatment in patients with biotinidase deficiency - Twenty years follow-up

INTRODUCTION

Biotinidase deficiency (BTD) is an inborn error of biotin metabolism inherited as an autosomal recessive trait. Due to the, biotinidase deficiency, biotin is not recycled. Individuals with BTD usually exhibit neurological and cutaneous abnormalities unless treated with biotin. Supplementation with biotin may either ameliorate or if early introduced even prevent symptoms when introduced presymptomatically.

PATIENTS AND METHODS

Since 1991, 22 Polish patients from 19 families have been diagnosed with BTD. In 16 children the diagnosis had been suspected on the basis of clinical signs: skin lesions, hyperventilation, seizures, spasticity, and laboratory investigation (elevated lactate and metabolites on urine organic acids profile). The defect was enzymatically (serum biotinidase activity measurement) and genetically (tested for mutations in the BTD gene) confirmed afterwards. All patients were treated with biotin. Urine organic acids analysis (GC/MS) for 3-hydroxizovaleric acid was used for patients' monitoring. Neurological, audiological and ophthalmological evaluation has been conducted once a year.

RESULTS

In 5 symptomatic patients a progressive optic nerve atrophy had already been noted at the time of treatment initiation. In these patients sensorineural hearing loss has also been diagnosed despite biotin supplementation. Asymptomatic patients treated with biotin supplementation presented no signs or symptoms of BTD. Supplementation with biotin slows the progression of BTD in symptomatic patients, but does not reverse nerve atrophy. Nonetheless, introduction of the treatment with biotin during presymptomatic stage of the disease prevents the onset of symptoms including optic atrophy and hearing loss. Homozygosity for the p.Leu215Phe mutation in BTD gene seems to be frequent in patients from the North-Eastern region of Poland and is connected with the hearing loss.

CONCLUSION

Since the prognosis for individuals diagnosed with BTD is good, provided they are treated before symptoms occur, it is justified to add this metabolic disorder to the panel of conditions screened under the national newborn screening programme in Poland.

Biotin in metabolism and molecular biology

Biotin is a water-soluble vitamin required by all organisms by virtue of its essential role in carboxylation reactions. Although the metabolism and role of biotin in intermediary metabolism are well established, biotin remains one of the most poorly understood water-soluble vitamins in terms of nutritional requirements and responsiveness to physiological and pharmacological states. Significant advances in the understanding of biotin nutriture have been recently accomplished through the description of the kinetics and regulation of biotin transport and improved methods for biotin status assessment. Additionally, the potential role of biotin in the regulation of gene expression has been strengthened through description of altered gene expression during biotin deficiency and through newly described enzymatic activities of the enzyme biotinidase. Given mounting evidence of suboptimum biotin status, a more complete understanding of these aspects of biotin should lead to a greater appreciation of the ways in which biotin aids in the maintenance of health.

Cerebral metabolic change after treatment in biotinidase deficiency

A 13.5-year-old boy with biotinidase deficiency was studied 8 days before and 5 months after biotin treatment by positron emission tomography (PET) and computerized electroencephalographic topography (CET). With biotin treatment there was a marked improvement in the presenting symptom of loss of visual acuity and a more modest recovery in spastic quadraparesis. By PET scanning, the relative metabolic rate for glucose was more than 2 standard deviations lower in the temporal and occipital cortices than in adult or age-matched controls. With biotin treatment, these values rose to normal limits for both control groups. By CET, normalized EEG equivalent to the relative glucose metabolic rate showed asymmetric slowing in the left temporal and frontal regions before treatment, whereas none of the 32 leads exceeded normal limits of delta, theta, alpha or beta after treatment. These results suggest a strong correlation between clinical, metabolic and electrical measures of brain function as related to biotin treatment in biotinidase deficiency.

Biotinidase deficiency: a rare cause of laryngeal stridor

A case of a child with a biotinidase deficiency who had a laryngeal stridor as a leading symptom is presented. This rare disease is distressing for diagnosis but easily treatable, if recognized. This condition, unless suspect clinically, could easily be overlooked and unnecessary tracheotomy could be done.

Multiple carboxylase deficiency

1. The multiple carboxylase deficiencies are inborn errors in the metabolism of biotin in which there is defective activity of propionyl CoA carboxylase, 3-methylcrotonyl CoA carboxylase and pyruvate carboxylase. 2. Two distinct disorders have been described. 3. In one the fundamental defect is in the enzyme holocarboxylase synthetase which catalyzes the molecular activation of the apocarboxylase proteins. 4. In the other the fundamental defect is in biotinidase which catalyzes the reutilization of biotin and may be involved in its digestion and intestinal absorption.