Fast-phase instabilities in normally sighted relatives of congenital nystagmus patients—autosomal dominant and x-chromosome recessive modes of inheritance

Abstract

Verification of inheritance in congenital nystagmus (CN) is only possible through the identification of more than one affected member in a family since in a single case there are no accurate clinical differentiations between "spontaneous" and inherited CN. We performed electronystagmographic examinations (ENG) to search for abnormal involuntary eye movements as a sign of heredity in seemingly unaffected members of CN families. ENG registrations were performed under three test conditions: (1) with the subject fixating a target, (2) with the room lights off and (3) with closed eyes. Fifty normally sighted individuals (group (a] underwent the test procedure to provide a baseline of normality. Five CN families (three dominant, two sex-linked recessive) were tested as group (b). The eye movement recordings were analysed in terms of nystagmus intensity (amplitude x frequency of the involuntary saccade). In every one of the five families, abnormalities in seemingly non-affected members could be demonstrated: in four families, fast-phase instabilities, in the fifth family a true (CN) (slow-phase instability). All certain gene carriers were diagnosed correctly by the ENG. These findings indicate a method for detecting slightly affected members in dominant pedigrees and female gene carriers in sex-linked mode of transmission.

The Molecular Genetics of Congenital Idiopathic Nystagmus

“…Subtle eye movement abnormalities have been detected among apparently unaffected relatives of CIN patients (Dell'Osso & Weissman, 1993;Shallo-Hoffmann & Watermeier, 1988) and it is also known that nystagmus waveform and phenotype may vary significantly, not only within pedigrees but even monozygotic twins with CIN. (Abadi & Dickinson, 1983;Spooner & Bateman, 1986) This may be of considerable importance for linkage projects using these CIN pedigrees where phenotypic variations may lead to errors in assigning affected/non-affected status.…”

Congenital nystagmus in a (46, XX/45,X) mosaic woman from a family with X‐linked congenital nystagmus

“…X-linked congenital nystagmus has been reported in association with red-green color blindness [Rucker, 1949;Pearce, 19781 or without any other abnormalities [Billings, 1942;Schneiderman et al, 1976;Shallo-Hoffmann et al, 1988;Pearce, 1978;Hayasaki, 19861. In some of these pedigrees, affected females have been described.…”