Genetic and phenotypic characterization of NKX6-2-related spastic ataxia and hypomyelination.

BACKGROUND AND PURPOSE: Hypomyelinating leukodystrophies are a heterogeneous group of genetic disorders with a wide spectrum of phenotypes and a high rate of genetically unsolved cases. Bi-allelic mutations in NKX6-2 were recently linked to spastic ataxia 8 with hypomyelinating leukodystrophy. METHODS: Using a combination of homozygosity mapping, exome sequencing, and detailed clinical and neuroimaging assessment a series of new NKX6-2 mutations in a multicentre setting is described. Then, all reported NKX6-2 mutations and those identified in this study were combined and an in-depth analysis of NKX6-2-related disease spectrum was provided. RESULTS: Eleven new cases from eight families of different ethnic backgrounds carrying compound heterozygous and homozygous pathogenic variants in NKX6-2 were identified, evidencing a high NKX6-2 mutation burden in the hypomyelinating leukodystrophy disease spectrum. Our data reveal a phenotype spectrum with neonatal onset, global psychomotor delay and worse prognosis at the severe end and a childhood onset with mainly motor phenotype at the milder end. The phenotypic and neuroimaging expression in NKX6-2 is described and it is shown that phenotypes with epilepsy in the absence of overt hypomyelination and diffuse hypomyelination without seizures can occur. CONCLUSIONS: NKX6-2 mutations should be considered in patients with autosomal recessive, very early onset of nystagmus, cerebellar ataxia with hypotonia that rapidly progresses to spasticity, particularly when associated with neuroimaging signs of hypomyelination. Therefore, it is recommended that NXK6-2 should be included in hypomyelinating leukodystrophy and spastic ataxia diagnostic panels.

Neuroimaging features of neurodegeneration with brain iron accumulation.

NBIA characterizes a class of neurodegenerative diseases that feature a prominent extrapyramidal movement disorder, intellectual deterioration, and a characteristic deposition of iron in the basal ganglia. The diagnosis of NBIA is made on the basis of the combination of representative clinical features along with MR imaging evidence of iron accumulation. In many cases, confirmatory molecular genetic testing is now available as well. A number of new subtypes of NBIA have recently been described, with distinct neuroradiologic and clinical features. This article outlines the known subtypes of NBIA, delineates their clinical and radiographic features, and suggests an algorithm for evaluation.

Identification of critical regions for clinical features of distal 10q deletion syndrome.

Array comparative genomic hybridization studies were performed to further characterize cytogenetic abnormalities found originally by karyotype and fluorescence in situ hybridization in five clinical cases of distal 10q deletions, including several with complex cytogenetic rearrangements and one with a partial male-to-female sex-reversal phenotype. These results have enabled us to narrow the previously proposed critical regions for the craniofacial, urogenital, and neuropsychiatric disease-related manifestations associated with distal 10q deletion syndrome. Furthermore, we propose that haploinsufficiency of the DOCK1 gene may play a crucial role in the pathogenesis of the 10q deletion syndrome. We hypothesize that alteration of DOCK1 and/or other genes involved in regulation and signaling of multiple pathways can explain the wide range of phenotypic variability between patients with similar or identical cytogenetic abnormalities.

The role of evidence-based medicine and clinical trials in rare genetic disorders.

The drive to empirically evaluate and analyze tools for the screening, diagnosis, management and monitoring of disease captured by the phrase 'evidence-based medicine (EBM)' has firmly entrenched itself as part of standard clinical care. However, rare genetic disorders, by their very nature, challenge the generation and application of EBM. This review presents many of the challenges encountered in applying EBM to rare genetic disorders, highlighting areas of recent emphasis in establishing multi-institutional collaborative research networks and in the systematic evaluation of developing therapies. Resources for identifying EBM tools for the practitioner are discussed, and the features and limitations of such resources are presented. Although the application of EBM to rare genetic disorders has definite limitations, a foundation has been established, and ongoing efforts seeking to systematically summarize and critically evaluate available evidence will continue to help identify the most effective tools for screening, diagnosis, management, and monitoring.

Insulin inhibition of the proteasome is dependent on degradation of insulin by insulin-degrading enzyme.

A consequence of insulin-dependent diabetes mellitus is the loss of lean muscle mass as a result of accelerated proteolysis by the proteasome. Insulin inhibition of proteasomal activity requires interaction with insulin-degrading enzyme (IDE), but it is unclear if proteasome inhibition is dependent merely on insulin-NIDE binding or if degradation of insulin by IDE is required. To test the hypothesis that degradation by IDE is required for proteasome inhibition, a panel of insulin analogues with variable susceptibility to degradation by IDE binding was used to assess effects on the proteasome. The analogues used were [Lys(B28), Pro(B29)]-insulin (lispro), [Asp(B10)]-insulin (Asp(B10)) and [Glu(B4), Gln(B16), Phe(B17)]-insulin (EQF). Lispro was as effective as insulin at inhibition of degradation of iodine-125 ((125)I)-labeled insulin, but Asp(B10) and EQF were somewhat more effective. All agents inhibited cross-linking of (125)I-insulin to IDE, suggesting that all were capable of IDE binding. In contrast, although insulin and lispro were readily degraded by IDE, Asp(B10) was degraded more slowly, and EQF degradation was undetectable. Both insulin and lispro inhibited the proteasome, but Asp(B10) was less effective, and EQF had little effect. In summary, despite effective IDE binding, EQF was poorly degraded by IDE, and was ineffective at proteasome inhibition. These data suggest that insulin inhibition of proteasome activity is dependent on degradation by IDE. The mechanism of proteasome inhibition may be the generation of inhibitory fragments of insulin, or by displacement of IDE from the proteasome.