Clinical, pathological and molecular findings in two siblings with giant axonal neuropathy (GAN): report from India

Giant axonal neuropathy (GAN, MIM: 256850) is characterized by an early onset of severe peripheral neuropathy, varying central nervous system involvement and strikingly frizzly hair. Mode of inheritance is autosomal recessive. Mutations in the gigaxonin (GAN) gene on chromosome 16q24.1 are frequently observed for this disorder, but genetic heterogeneity has been demonstrated for a milder variant of GAN. Gigaxonin binds C-terminally to various microtubule associated proteins causing their ubiquitin-mediated degradation. For several gigaxonin mutations it was shown that they hamper this process resulting finally in accumulation of microtubule associated proteins which may disturb cellular functions. Here, we report a family originating in India with two patients showing typical clinical signs suggestive of GAN.

Genomic DNA was analyzed for both siblings and their parents in order to detect the molecular changes in the GAN gene. The complete coding region including flanking sequences was amplified using published primer sequences. The PCR products were sequenced on both strands after purification using an ABI 3730 (Applied Biosystems) capillary sequencer. The resulting sequences were evaluated using SeqPilot (JSI-medical systems GmbH) and were compared to the reference sequences (NT_024797, NM_022041) given in the NCBI-database.

An AluYa5 insertion (c.1657ALUYa5ins, p.Thr553_Pro597del) in exon 11 of the GAN gene was identified homozygous in both siblings, whereas the parents were heterozygous carriers of this mutation. Here, the reported mutation is located in C-terminal part of the protein affecting the terminal kelch domain. Thus a functional important part of the protein is altered by the AluYa5 insertion and causes GAN.