Nrl-knockout mice deficient in Rpe65 fail to synthesize 11-cis retinal and cone outer segments

PURPOSE: To define rod and cone function further in terms of visual cycle mechanism, the retinal phenotype resulting from Rpe65 (retinoid isomerase I) deficiency in Nrl(-)(/)(-) mice having a single class of photoreceptors resembling wild-type cones was characterized and outcomes of retinoid supplementation evaluated. METHODS: Rpe65(-)(/)(-)/Nrl(-)(/)(-) mice were generated by breeding Rpe65(-)(/)(-) and Nrl(-)(/)(-) strains. Retinal histology, protein expression, retinoid content, and electroretinographic (ERG) responses were evaluated before and after treatment with 11-cis retinal by intraperitoneal injection. Results Retinas of young Rpe65(-)(/-)/Nrl(-)(/-) mice exhibited normal lamination, but lacked intact photoreceptor outer segments at all ages examined. Rpe65, Nrl, and rhodopsin were not detected, and S-opsin and M/L-opsin levels were reduced. Retinyl esters were the only retinoids present. In contrast, Nrl(-)(/)(-) mice exhibited decreased levels of retinaldehydes and retinyl esters, and elevated levels of retinols. ERG responses were elicited from Rpe65(-)(/-)/Nrl(-)(/-) mice only at the two highest intensities over a 4-log-unit range. Significant retinal thinning and outer nuclear layer loss occurred in Rpe65(-)(/-)/Nrl(-)(/-) mice with aging. Administration of exogenous 11-cis retinal did not rescue retinal morphology or markedly improve ERG responses. CONCLUSIONS: The findings provide clarification of reported cone loss of function in Rpe65(-)(/-)/Nrl(-)(/-) mice, now showing that chromophore absence results in destabilized cone outer segments and rapid retinal degeneration. The data support the view that rod-dominant retinas do not have a cone-specific mechanism for 11-cis retinal synthesis and have potential significance for therapeutic strategies for rescue of cone-rich retinal regions affected by disease in the aging human population.     

Phenytoin-induced cerebellar atrophy in an epileptic boy

Epilepsy is an important health problem due to its high prevalence and potential for causing long-term morbidity. It is commonly treated in children with phenytoin sodium. It has wide pharmacokinetic variability and a narrow therapeutic range that leads to toxicity. Here, we report a case of phenytoin-induced cerebellar atrophy in a 16-year-old epileptic boy who presented to the hospital with a viral infection.KEY WORDS: Adverse drug reaction, antiepileptic drugs, antiseizure drugs, cerebellar atrophy, phenytoin     

Latent autoimmune diabetes in adults: A distinct but heterogeneous clinical entity

Latent autoimmune diabetes in adults (LADA) accounts for 2%-12% of all cases of diabetes. Patients are typically diagnosed after 35 years of age and are often misdiagnosed as type II Diabetes Mellitus (DM). Glycemic control is initially achieved with sulfonylureas but patients eventually become insulin dependent more rapidly than with type II DM patients. Although they have a type II DM phenotype, patients have circulating beta (β) cell autoantibodies, a hallmark of type I DM. Alternative terms that have been used to describe this condition include type 1.5 diabetes, latent type I diabetes, slowly progressive Insulin Dependent Diabetes Mellitus, or youth onset diabetes of maturity. With regards to its autoimmune basis and rapid requirement for insulin, it has been suggested that LADA is a slowly progressive form of type I DM. However, recent work has revealed genetic and immunological differences between LADA and type I DM. The heterogeneity of LADA has also led to the proposal of criteria for its diagnosis by the Immunology of Diabetes Society. Although many workers have advocated a clinically oriented approach for screening of LADA, there are no universally accepted criteria for autoantibody testing in adult onset diabetes. Following recent advances in immunomodulatory therapies in type I DM, the same strategy is being explored in LADA. This review deals with the contribution of the genetic, immunological and metabolic components involved in the pathophysiology of LADA and recent approaches in screening of this distinct but heterogeneous clinical entity.     

Nuclear receptor NR2E3 gene mutations distort human retinal laminar architecture and cause an unusual degeneration

Mutations in the nuclear receptor gene, NR2E3, cause a disorder of human retinal photoreceptor development characterized by hyperfunction and excess of the minority S (short wavelength or blue) cone photoreceptor type, but near absence of function of the majority rod receptor. NR2E3 disease can also progress to blindness. How the human retina accommodates mis-specified types and numbers of neurons and advances to retinal degeneration are unknown. We studied the retinal organization in vivo of patients with NR2E3 mutations. Early human NR2E3 disease with S cone hyperfunction showed thickened retinal layers within an otherwise normally structured retina. With visual loss, however, lamination was coarse and there was a strikingly thick and bulging appearance to the retina, localized to an annulus encircling the central fovea. This pattern was not found in other retinal degenerations. The abnormal laminar retinal architecture of early NR2E3 disease may be due in part to larger cells with an S cone phenotype in place of rods that failed to differentiate. The later-stage dysplastic appearance suggests a previously unrecognized proliferative response in human retinal degeneration.     

Severe intellectual disability and autistic features associated with microduplication 2q23.1

We report on two patients with developmental delay, hypotonia, and autistic features associated with duplications of chromosome region 2q23.1-2q23.2 detected by chromosome microarray analysis. The duplications include one OMIM Morbid Map gene, MBD5, as well as seven known RefSeq genes (ACVR2A, ORC4L, EPC2, KIF5C, MIR1978, LYPD6B, and LYPD6). MBD5 lies in the minimum area of overlap of the 2q23.1 microdeletion syndrome. This report provides the first detailed clinical examination of two individuals with a duplication of this region and suggests that brain development and cognitive function may be affected by an increased dosage of the genes involved.