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HomePediatrics: General MedicineVitamin B-6 Dependency Syndromes

Vitamin B-6 Dependency Syndromes

Background

B6 dependency syndromes are a group of metabolic disorders which respond to large doses of vitamin B6. Although rare, pyridoxine-dependent seizure (PDS) is a recognized cause of intractable seizures in neonates, psychomotor developmental delay, and, sometimes, death in untreated patients.
Hunt et al first described PDS in 1954.
Since then, fewer than 100 cases have been reported worldwide.
Later onset seizures due to pyridoxine deficiency have been reported.
The 2 types of presentations are classic and atypical. The classic presentation consists of intractable seizures that appear within hours of birth and are resistant to conventional anticonvulsants. The seizures rapidly respond to administration of parenteral pyridoxine in doses greater than physiologic doses.
A trial of pyridoxine is recommended in all seizures that have no clear etiology and occur before the child is aged 18 months.
Atypicalformsinclude those with seizures only partly responsive to pyridoxine, referred to as pyridoxine responsive seizures, and those with late onset of seizures.
Despite treatment children can have intellectual deficits or developmental delays.

PDS is probably an underdiagnosed and underreported condition. All medical specialists should be aware of its existence and potentially favorable outcome.
Lifelong supplementation of pyridoxine is required.
Despite treatment developmental handicaps especially in expressive language are common.

Vitamin B-6 (pyridoxine)

See the list below:

Pyridoxine is water-soluble.

Sources include meat, nuts, and whole-grain products (especially wheat).

Deficiency usually occurs in conjunction with inadequate intake of other B vitamins due to poor diet or malabsorption states.

Isolated pyridoxine dependency can occur during treatment with isoniazid, which is a pyridoxine antagonist.

Pyridoxine requirements are increased in the presence of other drugs, including penicillamine, contraceptive steroids, and hydralazine.

Clinical features of deficiency in young infants include abnormal CNS activity (eg, irritability, aggravated startle response, seizures) and GI distress (eg, distension, vomiting, diarrhea).

Other manifestations include anemia, peripheral neuropathy, and dermatitis.

Treatment consists of pyridoxine 5 mg intramuscularly followed by 0.5 mg per day orally for 2 weeks. Correct dietary deficiency.

Consider pyridoxine dependency in the differential diagnosis of neonatal seizures when other more common causes have been eliminated. Rapid treatment with pyridoxine, 100 mg intramuscularly, is recommended.

The recommended daily dietary intake for pyridoxine is as follows:

Infants aged 0-6 months – 0.25 mg/d

Infants aged 7-12 months – 0.45 mg/d

Children aged 1-3 years – 0.6-0.9 mg/d

Children aged 4-7 years – 0.8-1.3 mg/d

Boys aged 8-11 years – 1.1-1.6 mg/d

Boys aged 12-15 years – 1.4-2.1 mg/d

Boys aged 16-18 years – 1.5-2.2 mg/d

Girls aged 8-11 years – 1-1.5 mg/d

Girls aged 12-15 years – 1.2-1.8 mg/d

Girls aged 16-18 years – 1.1-1.6 mg/d

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