Posterior Column Ataxia With Retinitis Pigmentosa

Posterior column ataxia retinitis pigmentosa (PCARP) with feline leukemia virus subgroup C cellular receptor 1 (FLVCR1) gene mutation is a rare disorder with significant ophthalmic features.

We conducted a retrospective case series study of patients diagnosed with PCARP and genetic testing positive for FLVCR1 mutation between 1 January 2015 and 1 October 2017 at the Children's Hospital of Pittsburgh. Clinical charts, visual fields, fundus autofluorescence, and spectral-domain optical coherence tomography (SD-OCT) were reviewed.

Seven patients from three families were identified to have PCARP and FLVCR1 mutation. The median age at presentation was 13 years (range, 7-28 years). Common clinical exam findings were astigmatism, cataracts, and vitreous syneresis. Funduscopy on all patients revealed bull's eye maculopathy, retinal vessels attenuation, and bone spicule changes in the peripheral retina. Fundus autofluorescence showed bilateral hyperautofluorescent rings. SD-OCT demonstrated morphological changes, which differed based on age. The youngest sibling family exhibited peripheral loss, but subfoveal preservation of the outer retinal layers. These layers were lost in the oldest sibling family. Visual fields loss paralleled SD-OCT findings.

There is limited published ophthalmic data on FLVCR1-related PCARP. We describe clinical and retinal imaging features in the one of the largest cohorts of affected patients in the literature. Given the availability of genetic testing for this phenotype, testing for FLVCR1 mutations should be considered in pediatric and adult patients with sensory ataxia and retinitis pigmentosa.

FLVCR1 (feline leukemia virus subgroup c receptor 1) is a transmembrane protein involved in the trafficking of intracellular heme. Homozygous variants in FLVCR1 have been described in association with a clinical syndrome of posterior column ataxia with retinitis pigmentosa (PCARP). Here, we describe a patient with non-syndromic retinitis pigmentosa homozygous for a splice-site variant in FLVCR1 (c.1092 + 5G>A) without evidence of posterior column ataxia or cerebellar degeneration. We suggest an association between intronic splice-site variants in FLVCR1 and the absence of posterior column degeneration and suggest a hypothesis to explain this observation. Should this association be proven, it would provide valuable prognostic information for patients. Retinal degeneration appears to be the sole clinical manifestation of this FLVCR1 variant; gene therapy approaches using an adeno-associated viral vector with sub-retinal delivery may therefore represent a therapeutic approach to halting retinal degeneration in this patient group.

FLVCR1 encodes for a ubiquitous heme exporter, whose recessive mutations cause posterior column ataxia with retinitis pigmentosa (PCARP). Recently, FLVCR1 recessive mutations were also found in two sporadic children with hereditary sensory-autonomic neuropathy (HSAN). We report the unique case of a 33-year-old Italian woman with a combination of typical PCARP, sensory-autonomic neuropathy with sensory loss to all modalities and multiple autonomic dysfuctions, and acute lymphocytic leukemia. Molecular analysis demonstrated homozygosity for the previously identified FLVCR1 p.Pro221Ser variation. The same variation, in combination with a frameshift mutation, was previously identified in an Italian child with HSAN. Functional studies carried out on patient-derived lymphoblastoid cell lines showed decreased FLVCR1a transcript, increased reactive oxygen species, excessive intracellular heme accumulation, and increased number of Annexin V positive cells. This indicates that the homozygous p.Pro221Ser FLVCR1 variation compromises the ability of FLVCR1a to export heme leading to enhanced susceptibility to programmed cell death. Our study demonstrates the existence of a phenotypic continuum among the discrete disorders previously linked to FLVCR1 mutations, and suggests that the related alteration of heme metabolism may lead to the degeneration of specific neuronal cell populations.