INTRODUCTION.
Nystagmus is a condition of involuntary eye movement. People can be born with it but more commonly acquire it in infancy or later in life. In many cases it may result in reduced or limited vision.
Classic congenital or infantile nystagmus presents as conjugate, horizontal oscillations of the eyes, in primary or eccentric gaze, often with a preferred head turn or tilt. Other associated features may include mildly decreased visual acuity, strabismus, astigmatism, and occasionally head nodding. Eye movement recordings reveal that infantile nystagmus is predominantly a horizontal jerk waveform, with a diagnostic accelerating velocity slow phase. However, pendular and triangular waveforms may also be present. The nystagmus may rarely be vertical. As these patients often have normal visual acuity, it is presumed that the nystagmus represents a primary defect in the parts of the brain responsible for ocular motor control; thus the disorder has sometimes been termed ‘congenital motor nystagmus‘.
There is evidence that nystagmus type-2 is caused by mutation in the NYS2 gene on cytogenetic location 6p12 and genomic coordinates 6:46,200,001-57,200,000. The screenshot of the NYS2 gene 11,000,000 bp (base pairs) of DNA sequence length is shown BELOW. Nine (9) other genes besides NYS2 in the 6p12 cytogenetic location are listed BENEATH.
| Coordinate | Symbol | Genomic Name |
| 6:45,880,827 | CLIC5 | Chloride intracellular channel 5 |
| 6:46,129,989 | ENPP4 | Ectonucleotide pyrophosphatase/phosphodiesterase 4 |
| 6:46,159,185 | ENPP5 | Ectonucleotide pyrophosphatase/phosphodiesterase 5 |
| 6:46,200,001 | CTRCT28 | Cataract 28 |
| 6:46,200,001 | NYS2 | Nystagmus 2, congenital, autosomal dominant |
| 6:46,220,736 | RCAN2 | Regulator of calcineurin 2 |
| 6:46,549,580 | CYP39A1 | Cytochrome P450, subfamily XXXIXA |
| 6:46,652,975 | SLC25A27 | Solute carrier family 25, member 17 |
| 6:46,680,268 | TDRD6 | TUDOR domain-containing protein 6 |
| 6:46,704,201 | PLA2G7 | Phospholipase A2, group VII |
