Phenotypic variability in patients with unique double homozygous mutations causing variant ataxia telangiectasia.

Ataxia-Telangiectasia (A-T) is a neurodegenerative disease caused by bi-allelic mutations in the Ataxia-Telangiectasia-Mutated (ATM) gene. Complete lack of ATM activity leads to severe A-T and mutations allowing for residual activity cause a milder phenotype, termed variant A-T. There are only sparse data on the variability in phenotypes of variant A-T patients carrying the same mutations. A retrospective study of 15 patients with variant A-T, all double homozygous for the same mutations was conducted. The age of first symptom ranged from 4-180 months, including: truncal ataxia at <18 months of age in 9 patients, ataxia and instability only during fever in one patient, dystonia in one patient and malignancy in 4 patients. Global developmental delay and occulo-motor apraxia were recorded in 4/14 patients. Variant A-T patients with the same mutations in ATM, have variable phenotypes. Environmental, epigenetic, and post translational factors are likely to play a role in creation of the phenotype in variant A-T patients.