ANNALS OF NEUROLOGY

Chelban V, Wilson MP, Warman Chardon J, Vandrovcova J, Zanetti MN, Zamba-Papanicolaou E, Efthymiou S, Pope S, Conte MR, Abis G, Liu YT, Tribollet E, Haridy NA, Botia JA, Ryten M, Nicolaou P, Minaidou A, Christodoulou K, Kernohan KD, Eaton A, Osmond M, Ito Y, Bourque P, Jepson JEC, Bello O, Bremner F, Cordivari C, Reilly MM, Foiani M, Heslegrave A, Zetterberg H, Heales SJR, Wood NW, Rothman JE, Boycott KM, Mills PB, Clayton PT and Houlden H.

Ann Neurol. 2019 Jun 11. doi: 10.1002/ana.25524.

Abstract

Objective:

To identify disease-causing variants in autosomal recessive axonal polyneuropathy with optic atrophy and provide targeted replacement therapy.

Methods:

We performed genome-wide sequencing, homozygosity mapping and segregation analysis for novel disease-causing gene discovery. We used circular dichroism to show secondary structure changes and isothermal titration calorimetry to investigate the impact of variants on ATP-binding. Pathogenicity was further supported by enzymatic assays and mass spectroscopy on recombinant protein, patient-derived fibroblasts, plasma and erythrocytes. Response to supplementation was measured with clinical validated rating scales, electrophysiology and biochemical quantification.

Results:

We identified bi-allelic mutations in PDXK in five individuals from two unrelated families with primary axonal polyneuropathy and optic atrophy. The natural history of this disorder suggests that untreated, affected individuals become wheelchair-bound and blind. We identified conformational rearrangement in the mutant enzyme around the ATP-binding pocket. Low PDXK ATP-binding resulted in decreased erythrocyte PDXK activity and low pyridoxal 5′-phosphate (PLP) concentrations. We rescued the clinical and biochemical profile with PLPsupplementation in one family, improvement in power, pain and fatigue contributing to patients regaining their ability to ambulate during the first year of PLP normalization.

Interpretation:

We show that mutations in PDXK cause autosomal recessive axonal peripheral polyneuropathy leading to disease via reduced PDXK enzymatic activity and low PLP. We show that the biochemical profile can be rescued with PLP supplementation associated with clinical improvement. As B6 is a cofactor in diverse essential biological pathways, our findings may have direct implications for neuropathies of unknown aetiology characterised by reduced PLP levels. This article is protected by copyright. All rights reserved.