GeneReviews NYS1

Clinical characteristics
FRMD7-related infantile nystagmus (FIN) is characterized by either the onset of horizontal, conjugate, gaze-dependent nystagmus in the first six months of life or periodic alternating nystagmus (with cyclical changes of nystagmus direction) of infantile onset. Binocular vision and color vision are normal and visual acuity is typically better than 6/12. An abnormal head posture is seen in approximately 15% of affected individuals. The eyes are structurally normal and electrophysiologic studies, such as visual evoked potential (VEP) and electroretinogram (ERG), are normal. Affected females report slightly better visual acuity than affected males; however, no differences between males and females in the amplitude, frequency, and waveform of nystagmus are observed.

The diagnosis is based on clinical findings (including, when possible, ocular motility recordings) and molecular genetic testing of FRMD7.

Treatment of manifestations: Routine correction of refractive errors; contact lenses that correct refractive errors may also dampen the intensity of the nystagmus. Prisms may be useful in those with binocular vision whose nystagmus is dampened by convergence. Memantine and gabapentin can improve intensity of nystagmus, foveation, and, hence, visual acuity. Surgical approaches include: horizontal rectus tenotomy to improve the waveform of the nystagmus and visual function and the Anderson-Kestenbaum procedure, surgery of the extraocular muscles to shift the null zone to the primary position in order to correct anomalous head posture.
Surveillance: Routine monitoring, especially during childhood, to evaluate visual acuity and development of refractive errors, strabismus, and/or ambylopia.

Genetic counseling
FIN is inherited in an X-linked manner. Affected males transmit the pathogenic variant to all of their daughters and none of their sons. Women who are carriers have a 50% chance of transmitting the pathogenic variant in each pregnancy. Carrier testing for at-risk female relatives and prenatal testing for pregnancies at increased risk are possible once the pathogenic variant has been identified in the family.