Molecular genetic analysis of trinucleotide repeat disorders (TRDs) in Indian population and application of repeat primed PCR

Molecular spectrum, family screening and genetic counselling of Spinocerebellar Ataxia (SCA) cases in an Indian scenario

Spinocerebellar Ataxia (SCA) is a heterogeneous adult-onset disorder with an autosomal dominant inheritance pattern mainly caused by triplet repeat expansions. Clinical diagnosis of SCA is based on phenotypic features followed by confirmation through molecular diagnosis. To identify status of repeat range in Indian SCA cases and provide extended family screening, we enrolled 70 clinical SCA suspects. For molecular diagnosis, multiplex PCR (M-PCR) was used for common Indian SCA subtypes 1, 2, 3, 6, 7, 10, 12 and 17. TP-PCR was further used in SCA2, 7 and 10 to identify larger expansions. Eighteen out of 70 SCA suspects (25%) were found to be positive for various SCA subtypes- (5 SCA1 (28%), 6 SAC2 (34%), 2 SCA3 (12%), 3 SCA7 (16%) and one each for SCA6 (1%) and SCA17 (1%) subtypes). Genetic counselling and extended family screening were offered to all positive cases and yielded additional nine cases. We have established M-PCR and TP-PCR to detect the CAG repeat expansion in SCA suspects. This method can confirm SCA subtypes in a reliable, rapid and cost-effective way. Genetic characterization of SCA-related genes has great clinical relevance, as it could provide additional information and guidance to clinicians and family members regarding prognosis.

DRPLA: understanding the natural history and developing biomarkers to accelerate therapeutic trials in a globally rare repeat expansion disorder

Dentatorubral–pallidoluysian atrophy (DRPLA) is a rare neurodegenerative disorder caused by CAG repeat expansions in the atrophin-1 gene and is inherited in an autosomal dominant fashion. There are currently no disease-modifying treatments available. The broad development of therapies for DRPLA, as well as other similar rare diseases, has hit a roadblock due to the rarity of the condition and the wide global distribution of patients and families, consequently inhibiting biomarker development and therapeutic research. Considering the shifting focus towards diverse populations, widespread genetic testing, rapid advancements in the development of clinical and wet biomarkers for Huntington’s disease (HD), and the ongoing clinical trials for antisense oligonucleotide (ASO) therapies, the prospect of developing effective treatments in rare disorders has completely changed. The awareness of the HD ASO program has prompted global collaboration for rare disorders in natural history studies and the development of biomarkers, with the eventual goal of undergoing treatment trials. Here, we discuss DRPLA, which shares similarities with HD, and how in this and other repeat expansion disorders, neurogenetics groups like ours at UCL are gearing up for forthcoming natural history studies to accelerate future ASO treatment trials to hopefully emulate the progress seen in HD.

[Fragile X syndrome and FMR1-dependent diseases - diagnostic scheme based on own experience .]

The presence of dynamic mutation in the FMR1 gene localized on the X chromosome (Xq28) is the major cause of Fragile X syndrome. As this syndrome is quite frequently diagnosed in patients with intellectual disability and autism spectrum disorders, the genetic testing of the FMR1 gene is a routine procedure performed in these patients. Molecular methods based on the PCR technique are used commonly, as they allow to identify normal (up to 54 CGG repeats, including grey zone alleles - 45-54 CGG repeats), premutation (55-200 CGG repeats) and full mutation (>200 CGG repeats) alleles.The article presents the basic methods used in the molecular diagnosis of Fragile X syndrome and other FMR1-related disorders. The following methods are presented: a screening test with GeneScan analysis, TP-PCR based tests and methods used for methylation analysis. Their pros and cons, as well as the resulting interpretation are discussed. Moreover, there is a presentation of the molecular diagnostic scheme following European Molecular Genetics Quality Network guidelines used in the Department of Medical Genetics.

Evaluating the current state of the art of Huntington disease research: a scientometric analysis

Huntington disease (HD) is an incurable neurodegenerative disorder caused by a dominant mutation on the 4th chromosome. We aim to present a scientometric analysis of the extant scientific undertakings devoted to better understanding HD. Therefore, a quantitative study was performed to examine the current state-of-the-art approaches that foster researchers’ understandings of the current knowledge, research trends, and research gaps regarding this disorder. We performed literature searches of articles that were published up to September 2016 in the “ISI Web of Science™” (http://apps.webofknowledge.com/). The keyword used was “Huntington disease”. Of the initial 14,036 articles that were obtained, 7732 were eligible for inclusion in the study according to their relevance. Data were classified according to language, country of publication, year, and area of concentration. The country leader regarding the number of studies published on HD is the United States, accounting for nearly 30% of all publications, followed by England and Germany, who have published 10 and 7% of all publications, respectively. Regarding the language in which the articles were written, 98% of publications were in English. The first publication to be found on HD was published in 1974. A surge of publications on HD can be seen from 1996 onward. In relation to the various knowledge areas that emerged, most publications were in the fields of neuroscience and neurology, likely because HD is a neurodegenerative disorder. Publications written in areas such as psychiatry, genetics, and molecular biology also predominated.