2013 Nov;260(11):2728-35. doi: 10.1007/s00415-013-7046-4. Epub 2013 Jul 25.

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Department of Neurology, Emory University School of Medicine, Wesley Woods Health Center, 1841 Clifton Road, NE, Suite 350, Atlanta, GA, 30329-4021, USA, aasefshaikh@gmail.com.


Ataxia-telangiectasia (A-T) is a progressive neurodegenerative disorder with prominent eye movement deficits localizing to the cerebellum. We sought to determine if 4-aminopyridine (4-AP), which putatively enhances the precision of Purkinje neurons, could improve the disorders of eye movements and vestibular function in A-T. The influence of 4-AP on disorders of eye movements and vestibular function was studied in four A-T patients. The effects on the cerebellar control of vestibulo-ocular reflex (VOR) was quantitatively assessed by the decay time constant of per- and post-rotational nystagmus during constant velocity en bloc rotations. The length of the VOR time constant determines the fidelity of the vestibular velocity storage, a neural mechanism that increases the bandwidth of VOR under cerebellar control. The VOR time constant was not increased in A-T patients. The latter is explained by the extent of cerebellar lesion as previously described in A-T and other cerebellar disorders. Nevertheless, 4-AP shortened the VOR time constant during horizontal rotations. Severe disinhibition of velocity storage in subjects with putatively profound cerebellar degeneration manifest periodic alternating nystagmus (PAN). Among two A-T subjects who manifested PAN, 4-AP reduced the peak slow phase velocity of the more severely affected individual and abrogated the PAN in the other. Two A-T subjects manifested horizontal and vertical spontaneous nystagmus (SN) in primary gaze, 4-AP reduced its slow phase velocity. We conclude that in subjects with A-T 4-AP has a prominent effect on the ocular motor and vestibular deficits that are ascribed to the loss of cerebellar Purkinje neurons.

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