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Huibert Jan Simonsz, M. Kooiker, J. J.M. Pel, M. M. van Genderen, Ralf Florijn, L.S. Smit, Maarten Kamermans, J. van der Steen; Onset of low-frequency, upgaze-evoked and high-frequency, horizontal nystagmus in infant with night-blindness associated, transient, tonic downgaze (NATTD). Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):2915.
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In 1994 we described infants who presented at age 2-4 months with tonic downgaze, chin-up head posture and low-frequency, upgaze-evoked nystagmus that disappeared at age 2, accompanied by high-frequency, horizontal nystagmus that persisted. In most of these, abnormal ERGs and CACNA1F, NYX or GPR179 mutations confirming CSNB were found. As the proteins affected by these mutations reside on either side of the rod-ON-bipolar synapse, and this pathway carries a motion signal, this specific combination of horizontal and vertical nystagmus may have a retinal cause. Early diagnosis of NATTD now permits longitudinal recording of the onset of upgaze-evoked and horizontal nystagmus.
A 4-months-old male infant, born prematurely (34 weeks, 2100g) presented with tonic downgaze and chin-up head posture. Eye movements were recorded with a Tobii X60 video eye tracker. Recording was repeated every 2 weeks from onset, later every 4-6 weeks. ERG was made in the months after.
A hemizygote mutation c.1784G>A; p.(Arg595His) was found in the CACNA1F gene. At 4 months (corrected age 11 weeks) the eyes were continuously in downgaze. Upper eyelid retraction occurred periodically without upward saccades. Slow horizontal pendular eye movements, disjugate and more pronounced in the right eye (Fig. 1), were accompanied by convergence spasms. At 4,5 months (corrected age 13 weeks) the horizontal pendular nystagmus had become more rapid with less convergence spasms. At 5,5 months (corrected age 17 weeks) horizontal eye movements had become more conjugate (Fig. 2); convergence spasms were rare. The infant occasionally tried to look ahead resulting in upward jerks with subsequent slow phases with deceleration back to downgaze, and eyelid retraction.
Tonic downgaze, accompanied by chin-up head posture, occurred as the primary event. The horizontal pendular nystagmus started with a minimal, hardly noticeable, pendular eye movement. A few weeks later upgaze-evoked nystagmus started when the infant tried to look ahead. In previous NATTD cases the upgaze-evoked nystagmus disappeared at around 2 years, in one case before 8 months. Interestingly, two of these were operated at age 10 for head posture, with the nulzone of the rapid horizontal nystagmus in upgaze.
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