Hereditary motor and sensory neuropathy (HMSN) Ia with cerebellar hypoplasia and ataxia

Introduction: Hereditary Motor and Sensory neuropathies (HMSN) are common inherited diseases with marked variability in phenotypic expression. In the past classification and diagnosis relied on clinical and electrophysiological features. Today molecular analysis of known mutations can establish diagnosis of HMSN. A duplication in the PMP-22-Gene is found predominantly in HMSN type Ia. It has been shown however, that certain mutations could cause different clinical entities.

Case Report: We report the case of an 8-year-old boy presenting with cerebellar symptoms like moderate ataxia and oculomotoric apraxia. The MRI showed a hypoplasia of the cerebellum. His mental development was normal. Examination revealed weakness of dorsiflexion of the feet, an atrophy of distal lower limbs and an absence of deep tendon reflexes. In addition the boy’s mother exhibited marked symmetrical pes cavus. Motor nerve conduction velocity was slowed in the mother (ulnar nerve 19,6 m/s) and the patient (tibial nerve 12,0 m/s and ulnar nerve 14,0 m/s).

Molecular analysis revealed a duplication of the peripherial Myeline-Proteine-Gene (PMP-22-Gene) in both patients confirming the diagnosis of HMSN Ia. Further studies excluded common disorders characterized by cerebellar symptoms (Friedreich ataxia, Ataxia teleangiectasia and Congenital disorders of Glycosylation).

Conclusion: HMSN Ia very rarely is associated with cerebellar symptoms. Despite the evidence of cerebellar hypoplasia with presumed pure cerebellar ataxia, motor nerve conduction studies should be undertaken to rule out HMSN. This case is an example for the phenotypic variability of these diseases.

Keywords: HMSN I, PMP-22-gene, ataxia, cerebellar hypoplasia