Abstract
Ataxia-telangiectasia-like disorder-1 (ATLD1, OMIM # 604391) is a very rare clini¬cal condition, characterized by slowly progres¬sive ataxia with onset in childhood, associated with oculomotor apraxia and dysarthria. Laboratory findings reveal increased susceptibility to radiation, with a defect in DNA repair. Patients with ATLD1 show no telangiectasia, have no immunodeficiency and also have preserved cognition. Reflexes might be initially brisk and later be¬come reduced associated with axonal sensorimotor neuropathy. Brain magnetic resonance imaging (MRI) detects cerebellar atrophy. The condition is caused by mutations in the MRE11A gene. The present study reports on the neurophysiologic finding in 8 Saudi patients, belonging to 3 Saudi families, who have genetically confirmed ATLD1. All investigated patients had cerebellar atrophy on brain MRI (5/5). Electrophysiologic studies showed normal motor conduction velocity (MCV) of median (8/8) and tibial (2/2) nerves, while 5/6 (83%) had normal peroneal nerve MCV. The distal motor latency (DML) for median, tibial and peroneal nerves was within the normal range in all examined patients. The amplitude of compound muscle action potential (CMAP) of median and tibial nerves was also normal, while that of the peroneal nerve was normal in 3/6 (50%). Two of seven (29%) patients had reduced amplitude of median nerve sensory nerve action potential (SNAP) while 3/8 (38%) had reduction in the amplitude of sural nerve SNAP. These findings favor an axonal type of neuropathy predominately affecting the sensory fibers (axonal sensorimotor neuropathy).The present study constitutes the largest cohort of ATLD1 patients worldwide who had electrophysiologic tests.

Key words: Ataxia-telangiectasia-like disorder-1 (ATLD1, OMIM # 604391), oculomotor apraxia and dysarthria, Pediatrics.