Caron, Elena MD; Burns, Dennis MD; Castro, Diana MD; Iannaccone, Susan T. MD, Journal of Clinical Neuromuscular Disease:
September 2015 - Volume 17 - Issue 1 - p 13–17, doi: 10.1097/CND.0000000000000086
Missense mutations are rare causes of Friedreich ataxia that can only be detected by sequencing of the FXN gene. Sequencing of the FXN gene is essential to make an early diagnosis when there is an atypical phenotype.
Source: Atypical Presentation for Friedreich Ataxia in a Child