Retinal function in deaf-blind syndromes

Abstract: A variety of disorders can cause retinal degeneration and hearing impairment, and it is of great value to have an early diagnosis since there is a large variation in phenotype and prognosis both within and between the different disorders. The general aim of this thesis was to characterize the retinal function, to describe the phenotype, and – where appropriate – to relate the phenotype to genotype in patients with combined visual and hearing impairment.

Alström syndrome is a rare autosomal recessive disease with variability in clinical phenotypes, and with visual impairment that progress to blindness in the teens. In Alström syndrome we have confirmed variability in the retinal function with different age of onset and rate of progression of the cone-rod degeneration, in which the final visual outcome could vary considerably.

Usher syndrome is a group of autosomal recessively inherited disorders. The three clinical phenotypes (Usher types 1, 2, and 3) have variability in onset, progression, and severity of the three characteristics: RP, sensory neural hearing loss, and vestibular dysfunction. In children with Usher syndrome ff-ERG under general anesthesia verified rod-cone degeneration with remaining rod function up to at least four years of age. The children had remaining cone responses to some extent, even in the early teens.
Phenotypic heterogeneity in Usher syndrome was established both in children and adults, including three families with siblings. Among the adults the phenotypic heterogeneity could be demonstrated both in siblings with the same genotype and between different genotypes of Usher syndrome, regarding both the severity of the rod-cone degeneration and the function in the macular region.

In children with Usher syndrome, Alström syndrome, Cockayne syndrome, and MPS we could confirm that in most children with retinal degeneration the appearance of the fundus often shows no or minor changes.

Ff-ERG in four rare syndrome-related disorders demonstrated in Alström syndrome cone-rod degeneration, in Cockayne syndrome rod-cone degeneration, in MPS 1H/S generalized degeneration of the photoreceptors, and in rubella retinopathy normal retinal function.

Examination of a control group of children with no retinal disorder establishes ff-ERG under general anesthesia as a reliable method.

Early examination with ff-ERG establishes the type of retinal degeneration, which is valuable in diagnosis, prognosis, and habituation to the visual handicap in deaf-blind syndromes. In combination with genetic screening, ff-ERG constitutes a valuable diagnostic tool.