Full-field electroretinography and marked variability in clinical phenotype of Alström syndrome.

OBJECTIVES: To characterize the clinical phenotype and to study the course of disease in patients with Alström syndrome, with an emphasis on retinal function assessed with full-field electroretinography (ERG). METHODS: Three age- and sex-matched patients with Alström syndrome were selected from our retinitis pigmentosa register for repeated ophthalmologic examinations that included tests for color vision and visual fields using Goldmann perimetry and for repeated assessment of full-field ERGs. RESULTS: Electroretinography demonstrated cone-rod degeneration in all 3 patients. A concomitant impairment of color vision and visual fields was also observed as well as marked variation in retinal function and in disease severity. CONCLUSIONS: Full-field ERGs confirmed that Alström syndrome is associated with a cone-rod type of retinal degeneration. In this study, we have shown a striking variability in retinal function and disease onset and severity, which has, to our knowledge, not been described previously in Alström syndrome.

Spectrum of ALMS1 variants and evaluation of genotype-phenotype correlations in Alström syndrome.

Alström syndrome is a monogenic recessive disorder featuring an array of clinical manifestations, with systemic fibrosis and multiple organ involvement, including retinal degeneration, hearing loss, childhood obesity, diabetes mellitus, dilated cardiomyopathy (DCM), urological dysfunction, and pulmonary, hepatic, and renal failure. We evaluated a large cohort of patients with Alström syndrome for mutations in the ALMS1 gene. In total, 79 disease-causing variants were identified, of which 55 are novel mutations. The variants are primarily clustered in exons 8, 10, and 16, although we also identified novel mutations in exons 12 and 18. Most alleles were identified only once (45/79), but several were found recurrently. Founder effects are likely in families of English and Turkish descent. We also identified 66 SNPs and assessed the functional significance of these variants based on the conserved identity of the protein and the severity of the resulting amino acid substitution. A genotype-phenotype association study examining 18 phenotypic parameters in a subset of 58 patients found suggestive associations between disease-causing variants in exon 16 and the onset of retinal degeneration before the age of 1 year (P = 0.02), the occurrence of urological dysfunction (P = 0.02), of DCM (P = 0.03), and of diabetes (P = 0.03). A significant association was found between alterations in exon 8 and absent, mild, or delayed renal disease (P = 0.0007). This data may have implications for the understanding of the molecular mechanisms of ALMS1 and provides the basis for further investigation of how alternative splicing of ALMS1 contributes to the severity of the disease.