Retinitis pigmentosa, ataxia, and peripheral neuropathy

Neuropathy, ataxia, retinitis pigmentosa: a case of a mother and two siblings

AIM

We describe the ophthalmic manifestations of Neuropathy, ataxia, retinitis pigmentosa (NARP) syndrome in three related patients.

METHODS

We examined a mother and her two children, who were carriers of the mt 8993T>G mutation. The mother, patient I, is the first known carrier within the family pedigree. Patients II and III are her children from a non-carrier father. NARP syndrome and the heteroplasmy levels were established prior to the first referral of the patients to the Ophthalmology department.We performed a visual acuity testing, followed by a biomicroscopic and fundus examination, as well as additional multimodal imaging testing: optical coherence tomography (OCT) and fundus autofluorescence (FAF), and functional testing: electroretinogram and visual field.

RESULTS

All patients had the clinical manifestations of NARP syndrome, which were variably expressed symptomatically, on the fundus exams, electroretinogram, and visual fields.

CONCLUSIONS

Once genetically established, NARP syndrome, as other mitochondrial disorders, has a very variable progression with different degrees of severity. A multimodal approach involving both neurological and ophthalmological diagnosis of NARP syndrome is necessary in order to establish the course of the disease and the measures to be taken.

Mutations in FLVCR1 cause posterior column ataxia and retinitis pigmentosa

The study of inherited retinal diseases has advanced our knowledge of the cellular and molecular mechanisms involved in sensory neural signaling. Dysfunction of two specific sensory modalities, vision and proprioception, characterizes the phenotype of the rare, autosomal-recessive disorder posterior column ataxia and retinitis pigmentosa (PCARP). Using targeted DNA capture and high-throughput sequencing, we analyzed the entire 4.2 Mb candidate sequence on chromosome 1q32 to find the gene mutated in PCARP in a single family. Employing comprehensive bioinformatic analysis and filtering, we identified a single-nucleotide coding variant in the feline leukemia virus subgroup C cellular receptor 1 (FLVCR1), a gene encoding a heme-transporter protein. Sanger sequencing confirmed the FLVCR1 mutation in this family and identified different homozygous missense mutations located within the protein's transmembrane channel segment in two other unrelated families with PCARP. To determine whether the selective pathologic features of PCARP correlated with FLVCR1 expression, we examined wild-type mouse Flvcr1 mRNA levels in the posterior column of the spinal cord and the retina via quantitative real-time reverse-transcriptase PCR. The Flvcr1 mRNA levels were most abundant in the retina, followed by the posterior column of the spinal cord and other brain regions. These results suggest that aberrant FLVCR1 causes a selective degeneration of a subpopulation of neurons in the retina and the posterior columns of the spinal cord via dysregulation of heme or iron homeostasis. This finding broadens the molecular basis of sensory neural signaling to include common mechanisms that involve proprioception and vision.

Posterior column ataxia and retinitis pigmentosa: a distinct clinical and genetic disorder

Autosomal recessive posterior column ataxia and retinitis pigmentosa (PCARP) is a movement disorder that was genetically mapped to a disease locus (AXPC1) on chromosome 1q32-q31 in an inbred population of Dutch-German ancestry in the continental United States. We performed genetic linkage analysis and haplotype reconstruction on a different family from Spain with an identical phenotype to determine if the neurologic signs of an early-onset ataxia, retinitis pigmentosa, and a sensory neuropathy also mapped to the AXPC1 locus. The disease phenotype was linked in the candidate interval with a maximum lod score of 3.56 at a recombination fraction of 0.0 for locus D1S414. Haplotypes were discordant and suggested that the disease mutation arose independently from at least two populations. These results refine the classification of early-onset ataxia, abrogate a founder effect for this recessive disorder, and provide evidence that PCARP is a distinct, homogeneous, clinical, and genetic disorder.

Spinocerebellar ataxia, hypogonadotropic hypogonadism, and choroidal dystrophy (Boucher-Neuhäuser syndrome)

We describe two families (including one previously reported) in which cerebellar or spinocerebellar ataxia, hypogonadotropic hypogonadism, and choroidal dystrophy result from abnormal function of an autosomal recessive gene. Review of the literature adds one other family with this disorder. These three examples confirm the existence of this traid as a specific, pleiotropic, single-gene syndrome. Careful ophthalmologic evaluation of patients with ataxia and hypogonadotropic hypogonadism may identify additional cases.

Retinitis pigmentosa

Retinitis pigmentosa is a clinically and genetically heterogeneous group of hereditary disorders in which there is progressive loss of photoreceptor and pigment epithelial function. The prevalence of retinitis pigmentosa is between 1/3000 and 1/5000 making it one of the most common causes of visual impairment in all age groups. The natural history, differential diagnosis, diagnostic clinical and electrophysiologic findings are reviewed. Generalization about the different genetic subtypes of retinitis pigmentosa are reviewed along with the uses of DNA probes for linkage studies. Syndromes in which retinitis pigmentosa is a manifestation are summarized.

Neurological disorders and phytanic acid metabolism

Fifty patients with neurological symptoms and signs resembling those of Refsum's disease were analyzed for phytanic acid in serum. In addition, the phytanic acid oxidase capacity in skin fibroblasts was determined. The patients suffered from retinitis pigmentosa, cerebellar ataxia and/or chronic polyneuropathy of unknown cause. The serum level of phytanic acid was not increased, and the alpha-oxidation of (1-14C) phytanic acid was found to be normal in all patients. The present investigation lends no support to the theory that so-called atypical or mild cases of Refsum's disease exist. This disorder appears to be a disease entity with a specific genetic phenotype.