Pyridoxine-dependent epilepsy

Pyridoxine-dependent epilepsy
Synonyms	Pyridoxine-dependent seizure (PDS), vitamin B6 responsive epilepsy
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Field	Neurology
Symptoms
Complications
Onset
Duration
Types
Causes
Risks
Diagnosis
Differential diagnosis
Prevention
Treatment
Medication
Prognosis
Frequency
Deaths

Pyridoxine-dependent epilepsy (PDE) is a rare genetic disorder characterized by intractable seizures in the prenatal and neonatal period. The disorder was first recognized in the 1950s, with the first description provided by Hunt et al. in 1954.<ref name=Gospe>,

 Pyridoxine-Dependent Epilepsy, 
 GeneReviews, 
 
 
 
 
 PMID: 20301659,
 
 
 Full text,</ref><ref name=Stockler>, 
 Pyridoxine dependent epilepsy and antiquitin deficiency: Clinical and molecular characteristics and recommendations for diagnosis, treatment and follow-up, 
 Molecular Genetics and Metabolism, 
 
 Vol. 104(Issue: 1–2),
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 DOI: 10.1016/j.ymgme.2011.05.014,
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 Global brain dysfunction in an infant with pyridoxine dependency: evaluation with EEG, evoked potentials, MRI, and PET., 
 Neurology, 
 
 Vol. 47(Issue: 3),
 pp. 824–6,
 DOI: 10.1212/WNL.47.3.824,
 PMID: 8797489,
 
 
 Full text,</ref>   More recently, pathogenic variants within the ALDH7A1 gene have been identified to cause PDE.<ref name=Gospe /><ref name=Stockler /><ref name=Shih /><ref name=Pearl>, 
 Pyridoxine or pyridoxal-5'-phosphate for neonatal epilepsy: the distinction just got murkier., 
 Neurology, 
 
 Vol. 82(Issue: 16),
 pp. 1392–4,
 DOI: 10.1212/WNL.0000000000000351,
 PMID: 24658927,</ref>

Genetics

PDE is inherited in an autosomal recessive manner and is estimated to affect around 1 in 400,000 to 700,000 births, though one study conducted in Germany estimated a prevalence of 1 in 20,000 births.<ref name=Gospe /><ref name=Stockler /> The ALDH7A1 gene encodes for the enzyme antiquitin or α -aminoadipic semialdehyde dehydrogenase, which is involved with the catabolism of lysine.<ref name=Gospe /><ref name=Stockler /><ref name=Pearl /><ref name=Parsley>,

 The patient with infantile seizures., 
 Current Opinion in Pediatrics, 
 
 Vol. 23(Issue: 6),
 pp. 693–9,
 DOI: 10.1097/MOP.0b013e32834b930c,
 PMID: 21926623,</ref>

Treatment

Patients with PDE do not respond to anticonvulsant medications, but seizures rapidly cease with therapeutic intravenous doses of Vitamin B6 and remission from seizures are often maintained on daily therapeutic doses of Vitamin B6.<ref name=Gospe /><ref name=Stockler /><ref name=Parsley /> An optimal dose has not yet been established, but doses of 50–100 mg/day or 15–30 mg/kg/day have been proposed.<ref name=Gospe /><ref name=Stockler /> Importantly, excessive doses of vitamin B6 can result in irreversible neurological damage, and therefore several guidelines recommend 500 mg per day as the maximal daily dose.<ref name=Gospe /><ref name=Stockler />

Despite remission of seizure activity with vitamin B6 supplementation, intellectual disability is frequently seen in patients with PDE.<ref name=Stockler /><ref name=vanKarnebeek>,

 Lysine restricted diet for pyridoxine-dependent epilepsy: First evidence and future trials, 
 Molecular Genetics and Metabolism, 
 
 Vol. 107(Issue: 3),
 pp. 335–344,
 DOI: 10.1016/j.ymgme.2012.09.006,
 PMID: 23022070,</ref>  Because the affected enzyme antiquitin is involved in the cerebral lysine degradation pathway, lysine restriction as an additional treatment modality has recently been explored.  Studies have been published which demonstrate potential for improved biomarkers, development, and behavior in patients treated with lysine restriction in addition to pyridoxine supplementation.<ref name=Stockler /><ref name=vanKarnebeek />  In trial, lysine restriction of 70–100 mg/kg/day in children less than 1 year of age, 45–80 mg/kg/day in children between 1–7 years of age, and 20–45 mg/kg/day in children older than 7 years of age were prescribed.<ref name=vanKarnebeek />  Despite the potential of additional benefit from lysine restriction, vitamin B6 supplementation remains the main-stay of treatment given lack of studies thus far demonstrating the safety and efficacy of lysine restriction for this purpose.

Monitoring

Plasma and cerebrospinal fluid levels of pipecolic acid are frequently elevated in patients with PDE, though it is a non-specific biomarker.<ref name=Gospe /><ref name=Stockler /><ref name=Parsley /> α-aminodipic semialdehyde is elevated in urine and plasma and is a more specific biomarker for PDE.<ref name=Gospe /><ref name=Stockler /><ref name=Parsley /> Improvements in these biomarkers have been reported with the implementation of a lysine-restricted diet.<ref name=Stockler /><ref name=Parsley /> Initial studies evaluating the safety and efficacy of lysine restriction evaluated developmental and cognitive outcomes by age-appropriate tests and parental observations.<ref name=vanKarnebeek />

See also

• Pyridoxine deficiency

External links

• GeneReview/NCBI/NIH/UW entry on Pyridoxine-Dependent Seizures
• Pyridoxine-dependent epilepsy. Genetics Home Reference. June 17, 2013.

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