Footnotes

• Contributors AE and AP collected the clinical data and wrote the first draft of the manuscript. MP and PLC made clinical evaluations of the patients, revised the draft and contributed to the final manuscript. CA performed all the genetic evaluations. FC followed the clinical course of patients over the years, performed the instrumental procedures and revised the final manuscript. FT contributed to the patients’ clinical evaluation. Each author listed on the manuscript has seen and approved the submission of this version of the manuscript and takes full responsibility for same.

• Funding This research received no specific grant from any funding agency in the public, commercial or not-for-profit sectors.

• Competing interests None declared.

• Patient consent Parental/guardian consent obtained.

• Provenance and peer review Not commissioned; internally peer reviewed.