Mitochondrial diagnosis revisited

Clinicopathological Relationships in an Aged Case of DOORS Syndrome With a p.Arg506X Mutation in the ATP6V1B2 Gene

DOORS [deafness, onychodystrophy, osteodystrophy, intellectual disability (mental retardation), and seizures] syndrome can be caused by mutations in the TBC1D24 and ATP6V1B2 genes, both of which are involved in endolysosomal function. Because of its extreme rarity, to date, no detailed neuropathological assessment has been performed to establish clinicopathological relationships and, thereby, understand better the neurobiology of this disease in aged cases. Accordingly, the aim of the current study was to highlight the clinicopathological characteristics of a novel case with a presumable de novo mutation in the ATP6V1B2 gene from a neuropathological point of view. This Caucasian male patient, who died at the age of 72 years, presented all the typical cardinal signs of DOORS syndrome. In addition, behavioral alterations, pyramidal signs, and Parkinsonism were observed. The p.R506X pathogenic mutation identified in the ATP6V1B2 gene was responsible for the clinical phenotype. The detailed neuropathological assessment revealed a limbic-predominant tauopathy in the forms of argyrophilic grain disease, primary age-related tauopathy, and age-related tau-astrogliopathy. In summary, we present the first detailed clinicopathological report of a patient with DOORS syndrome harboring a pathogenic mutation in the ATP6V1B2 gene. The demonstrated tauopathy may be considered as a consequence of lysosomal and/or mitochondrial dysfunction, similar to that found in Niemann-Pick type C disease, which is another lysosomal disorder characterized by premature neurodegenerative disorder.

Catalogue of inherited disorders found among the Irish Traveller population

Background Irish Travellers are an endogamous, nomadic, ethnic minority population mostly resident on the island of Ireland with smaller populations in Europe and the USA. High levels of consanguinity result in many rare autosomal recessive disorders. Due to founder effects and endogamy, most recessive disorders are caused by specific homozygous mutations unique to this population. Key clinicians and scientists with experience in managing rare disorders seen in this population have developed a de facto advisory service on differential diagnoses to consider when faced with specific clinical scenarios.

Objective(s) To catalogue all known inherited disorders found in the Irish Traveller population.

Methods We performed detailed literature and database searches to identify relevant publications and the disease mutations of known genetic disorders found in Irish Travellers.

Results We identified 104 genetic disorders: 90 inherited in an autosomal recessive manner; 13 autosomal dominant and one a recurring chromosomal duplication.

Conclusion We have collated our experience of inherited disorders found in the Irish Traveller population to make it publically available through this publication to facilitate a targeted genetic approach to diagnostics in this ethnic group.

Mining for mitochondrial mechanisms: Linking known syndromes to mitochondrial function

Mitochondrial disorders (MDs) are caused by defects in 1 or multiple complexes of the oxidative phosphorylation (OXPHOS) machinery. MDs are associated with a broad range of clinical signs and symptoms, and have considerable clinical overlap with other neuromuscular syndromes. This overlap might be due to involvement of mitochondrial pathways in some of these non-mitochondrial syndromes. Here, we give an overview of around 25 non-mitochondrial syndromes, diagnosed in patients who were initially suspected to have a MD on the basis of clinical and biochemical parameters. In addition, we highlight the mitochondrial connections of 6 of these non-mitochondrial syndromes (eg, Rett syndrome and Dravet syndrome) diagnosed in multiple patients. Further research to unravel the interplay between these genes and mitochondria may help to increase knowledge on these syndromes. Additionally, it may open new avenues for research on pathways interacting with mitochondrial function in order to find new targets for therapeutics to treat MDs. The data presented in this review underline the importance of careful assessment of clinical, genetic, and biochemical data in all patients suspected of a neuromuscular syndrome, and highlights the importance of the role of clinical geneticists, physicians, and clinical biochemists in recognizing the possible mitochondrial connection of non-mitochondrial syndromes.