Introduction

A 26-year-old woman (patient 1 on the family tree—figure 1) gave a 6-year history of dysarthria, occasional jerks and progressive gait unsteadiness with frequent falls, and had become bedridden. On examination, she had dorsal kyphosis and pes cavus. There was severe truncal and appendicular ataxia, generalised action myoclonus, hyporeflexia, hypotonia and bilateral extensor plantar reflexes. Electromyography with nerve conduction studies identified a sensorimotor polyneuropathy, with intermediate conduction velocities.

Her medical history was unremarkable, with a normal development. She had experienced one recent generalised tonic–clonic seizure. She had an older sister (patient 2 on the family tree—figure 1) with a rapidly progressive nephrotic syndrome starting at the age of 17, becoming steroid resistant and needing haemodialysis after a few months. She also had a normal development and unremarkable medical history. At age of 21, she had developed action myoclonus of the lower limbs, with subjective loss of strength and frequent falls, later progressing to the upper limbs. She started having generalised tonicclonic seizures and lost walking ability in the next year. At aged 28 years, she underwent renal transplantation and died 5 years later due to graft-related complications. Their parents were consanguineous (they were half-siblings) and they had a healthy sister.