A Review of the Ocular Phenotype and Correlation with Genotype in Poretti-Boltshauser Syndrome.

Background and Objectives: Poretti-Boltshauser syndrome (PBS) is a rare, autosomal recessive disorder caused by pathogenic variants in the LAMA1 gene, resulting in laminin dysfunction. This manifests as a cerebellar malformation with cysts, and patients present with developmental delay and ataxia; however, ocular features are not well-characterised. We aimed to summarise the ocular phenotypes of PBS based on cases reported in the literature. Materials and Methods: A literature search was conducted on Medline, Embase, and PubMed on PBS and its ocular associations. Genetically confirmed PBS cases were reviewed, and genotype-phenotype correlations were investigated. Results: Comprehensive reporting of genotypes and associated systemic and ocular phenotypes was available in 51 patients with PBS, who had 52 distinct variants in LAMA1. Most patients carried homozygous variants. The most common genotype was a c.2935delA homozygous mutation, followed by the c.768+1G>A; c.6701delC compound heterozygous mutation. High myopia was the most common ocular phenotype (n = 39), followed by strabismus (n = 27) and ocular motor apraxia (n = 26). A wide range of other ocular manifestations, including retinal dystrophy, retinal neovascularisation, retinal detachment, strabismus, nystagmus, optic disc and iris hypoplasia, were reported. Patients with the same genotype exhibited variable expressivity. Conclusions: PBS has a broad ocular phenotypic spectrum, and characterisation of this variability is important for making an accurate diagnosis and informing genetic counselling.