Preimplantation genetic diagnosis of spinocerebellar ataxia 3 by (CAG)n repeat detection

PGT-M for spinocerebellar ataxia type 1: development of a STR panel and a report of two clinical cases

PURPOSE

To present the developed preimplantation genetic testing (PGT) for spinocerebellar ataxia type 1 (SCA1) and the outcomes of IVF with PGT.

METHODS

PGT was performed for two unrelated couples from the Republic of Sakha (Yakutia) with the risk of SCA1 in one spouse. We have developed a system for PGT of a monogenic disease (PGT-M) for SCA1, which includes the analysis of a panel of 11 polymorphic STR markers linked to the ATXN1 gene and a pathogenic variant of the ATXN1 gene using nested PCR and fragment analysis. IVF/ICSI programs were performed according to standard protocols. Multiple displacement amplification (MDA) was used for whole genome amplification (WGA) and array comparative genomic hybridization (aCGH) for aneuploidy testing (PGT-A).

RESULTS

Eight STRs were informative for the first couple and ten for the second. Similarity of the haplotypes carrying pathogenic variants of the ATXN1 gene was noted. In the first case, during IVF/ICSI-PGT, three embryos reached the blastocyst stage and were biopsied. One embryo was diagnosed as normal by maternal STR haplotype and the ATXN1 allele. PGT-A revealed euploidy. The embryo transfer resulted in a singleton pregnancy, and a healthy boy was born. Postnatal diagnosis confirmed normal ATXN1. In the second case, two blastocysts were biopsied. Both were diagnosed as normal by PGT-M, but PGT-A revealed aneuploidy.

CONCLUSION

Birth of a healthy child after PGT for SCA1 was the first case of successful preimplantation prevention of SCA1 for the Yakut couple and the first case of successful PGT for SCA1 in Russia.

Review: Preimplantation genetic diagnosis (PGD) as a reproductive option in patients with neurodegenerative disorders

Preimplantation genetic diagnosis (PGD) was introduced in the late 1980s and represents an option for couples at risk of transmitting an inherited, debilitating or neurological disorder to their children. From a cleavage or blastocyst stage embryo, cell(s) are collected and then genetically analyzed for disease; enabling an unaffected embryo to be transferred into the uterus cavity. Nowadays, PGD has been carried out for several hundreds of heritable conditions including myotonic dystrophy, and for susceptibility genes involved in cancers of the nervous system. Currently, advanced molecular technologies with better resolution, such as array comparative genomic hybridisation, quantitative polymerase chain reaction, and next generation sequencing, are on the verge of becoming the gold standard in embryo preimplantation screening. Given this, it may be time for neurological societies to consider the published evidence to develop new guidelines for the integration of PGD into modern preventative neurology. Therefore, the main aim of this review is to illustrate the option of PGD to enable conception of an unaffected baby, and to assist clinicians and neurologists in the counseling of the patient at risk of transmitting an inherited disease, to explore the genetic journey throughout in vitro fertilization IVF with PGD.

Mesenchymal Stromal Cells' Therapy for Polyglutamine Disorders: Where Do We Stand and Where Should We Go?

Polyglutamine (polyQ) diseases are a group of inherited neurodegenerative disorders caused by the expansion of the cytosine-adenine-guanine (CAG) repeat. This mutation encodes extended glutamine (Q) tract in the disease protein, resulting in the alteration of its conformation/physiological role and in the formation of toxic fragments/aggregates of the protein. This group of heterogeneous disorders shares common molecular mechanisms, which opens the possibility to develop a pan therapeutic approach. Vast efforts have been made to develop strategies to alleviate disease symptoms. Nonetheless, there is still no therapy that can cure or effectively delay disease progression of any of these disorders. Mesenchymal stromal cells (MSC) are promising tools for the treatment of polyQ disorders, promoting protection, tissue regeneration, and/or modulation of the immune system in animal models. Accordingly, data collected from clinical trials have so far demonstrated that transplantation of MSC is safe and delays the progression of some polyQ disorders for some time. However, to achieve sustained phenotypic amelioration in clinics, several treatments may be necessary. Therefore, efforts to develop new strategies to improve MSC's therapeutic outcomes have been emerging. In this review article, we discuss the current treatments and strategies used to reduce polyQ symptoms and major pre-clinical and clinical achievements obtained with MSC transplantation as well as remaining flaws that need to be overcome. The requirement to cross the blood-brain-barrier (BBB), together with a short rate of cell engraftment in the lesioned area and low survival of MSC in a pathophysiological context upon transplantation may contribute to the transient therapeutic effects. We also review methods like pre-conditioning or genetic engineering of MSC that can be used to increase MSC survival in vivo, cellular-free approaches-i.e., MSC-conditioned medium (CM) or MSC-derived extracellular vesicles (EVs) as a way of possibly replacing the use of MSC and methods required to standardize the potential of MSC/MSC-derived products. These are fundamental questions that need to be addressed to obtain maximum MSC performance in polyQ diseases and therefore increase clinical benefits.

Preimplantation Genetic Diagnosis of Neurodegenerative Diseases: Review of Methodologies and Report of Our Experience as a Regional Reference Laboratory

Preimplantation genetic diagnosis (PGD) has become a crucial approach in helping carriers of inherited disorders to give birth to healthy offspring. In this study, we review PGD methodologies and explore the use of amplification refractory mutation system quantitative polymerase chain reaction (ARMS-qPCR) and/or linkage analysis for PGD in neurodegenerative diseases that are clinically relevant with typical features, such as late onset, and which are severely debilitating. A total of 13 oocyte retrieval cycles were conducted in 10 cases with various neurodegenerative diseases. Among the 59 embryos analyzed, 49.2% (29/59) were unaffected and 50.8% (30/59) were affected. Of the 12 embryo transfer cycles, three resulted in pregnancy, and all pregnancies were delivered. The implantation rate and livebirth rate were 23.1% (3/13) per oocyte retrieval cycle and 25.0% (3/12) per embryo transfer cycle. Allele dropout (ADO) was noted in two embryos that were classified as unaffected by ARMS-qPCR but were evidenced as affected after prenatal diagnosis, rendering the false negative rate as 6.3% (2/32). Four among the 13 cycles underwent PGD by ARMS-qPCR coupled with linkage analysis, and all were correctly diagnosed. We conclude that PGD by ARMS-qPCR and/or linkage analysis is a feasible strategy, whereas ADO is a concern when ARMS-qPCR is used as the sole technology in PGD, especially in autosomal dominant diseases.

Current concepts in the treatment of hereditary ataxias

Hereditary ataxias (HA) represents an extensive group of clinically and genetically heterogeneous neurodegenerative diseases, characterized by progressive ataxia combined with extra-cerebellar and multi-systemic involvements, including peripheral neuropathy, pyramidal signs, movement disorders, seizures, and cognitive dysfunction. There is no effective treatment for HA, and management remains supportive and symptomatic. In this review, we will focus on the symptomatic treatment of the main autosomal recessive ataxias, autosomal dominant ataxias, X-linked cerebellar ataxias and mitochondrial ataxias. We describe management for different clinical symptoms, mechanism-based approaches, rehabilitation therapy, disease modifying therapy, future clinical trials and perspectives, genetic counseling and preimplantation genetic diagnosis.

Psychological well-being and family satisfaction levels five years after being confirmed as a carrier of the Machado-Joseph disease mutation

The present study on long-term outcome of presymptomatic testing for Machado-Joseph disease (MJD) aimed to evaluate the psychological well-being and the familial satisfaction of subjects that 5 years prior received an unfavorable result in the predictive testing (PT). The study included 47 testees of Azorean origin (23 from the island of Flores and 24 from S. Miguel) that completed the fourth evaluation session of the MJD protocol, and undertook a neurological examination at the moment of participation in the study. Nearly 50% of testees were symptomatic at the time of the study. Psychological well-being of the 47 participants was evaluated using the Psychological General Well-Being Index (PGWB). The family satisfaction scale by adjectives was applied to obtain information on family dynamics. The average PGWB score of the total participants was of 73.3, a value indicative of psychological well-being. Nearly half of the testees presented scores indicating psychological well-being, whereas scores indicating moderate (28.9%) or severe (23.7%) stress were found in the remaining. The average score in the PGWB scale was lower in symptomatic than in asymptomatic subjects; moreover, the distinct distribution of the well-being categories seen in the two groups shows an impact of the appearance of first symptoms on the psychological state. Motives for undertaking the test, provided 5 years prior, failed to show an impact in well-being. The average score for familial satisfaction was of 134, a value compatible with high familial satisfaction, which represented the most frequent category (59.6%). Results demonstrate that well-being and family satisfaction need to be monitored in confirmed carriers of the MJD mutation. The inclusion of acceptance studies, after PT, as well as the development of acceptance training actions, should be of major importance to anticipate the possibility of psychological damage.

Machado-Joseph Disease: from first descriptions to new perspectives

Machado-Joseph Disease (MJD), also known as spinocerebellar ataxia type 3 (SCA3), represents the most common form of SCA worldwide. MJD is an autosomal dominant neurodegenerative disorder of late onset, involving predominantly the cerebellar, pyramidal, extrapyramidal, motor neuron and oculomotor systems; although sharing features with other SCAs, the identification of minor, but more specific signs, facilitates its differential diagnosis. MJD presents strong phenotypic heterogeneity, which has justified the classification of patients into three main clinical types. Main pathological lesions are observed in the spinocerebellar system, as well as in the cerebellar dentate nucleus. MJD's causative mutation consists in an expansion of an unstable CAG tract in exon 10 of the ATXN3 gene, located at 14q32.1. Haplotype-based studies have suggested that two main founder mutations may explain the present global distribution of the disease; the ancestral haplotype is of Asian origin, and has an estimated age of around 5,800 years, while the second mutational event has occurred about 1,400 years ago. The ATXN3 gene encodes for ataxin-3, which is ubiquitously expressed in neuronal and non-neuronal tissues, and, among other functions, is thought to participate in cellular protein quality control pathways. Mutated ATXN3 alleles consensually present about 61 to 87 CAG repeats, resulting in an expanded polyglutamine tract in ataxin-3. This altered protein gains a neurotoxic function, through yet unclear mechanisms. Clinical variability of MJD is only partially explained by the size of the CAG tract, which leaves a residual variance that should be explained by still unknown additional factors. Several genetic tests are available for MJD, and Genetic Counseling Programs have been created to better assist the affected families, namely on what concerns the possibility of pre-symptomatic testing. The main goal of this review was to bring together updated knowledge on MJD, covering several aspects from its initial descriptions and clinical presentation, through the discovery of the causative mutation, its origin and dispersion, as well as molecular genetics aspects considered essential for a better understanding of its neuropathology. Issues related with molecular testing and Genetic Counseling, as well as recent progresses and perspectives on genetic therapy, are also addressed.

[Gene diagnosis and CAG repeat analysis of spinocerebellar ataxia cases of Guangxi region]

To characterize the distributions and subtypes of the spinocerebellar ataxias (SCA) in Guangxi region, the SCAl, SCA2, SCA3/MJD, SCA6, SCA7 and SCA12 (CAG)n mutations were analyzed by polymerase chain reaction (PCR) and capillary electrophoresis (CE). The SCA3/MJD mutation was detected in a total of 21 SCA patients and 19 presymptomatic individuals from 6 SCA families and their CAG repeat numbers were 59-70 and 60-73, respectively. No (CAG)n mutations of SCA1, SCA2, SCA6, SCA7 and SCA12 were detected. This study showed that SCA in Guangxi region is mostly SCA3/MJD subtype and the CAG repeats are smaller than those reported in other regions previously.

Validation of preimplantation genetic diagnosis by PCR analysis: genotype comparison of the blastomere and corresponding embryo, implications for clinical practice

The aim of this study was to validate the overall preimplantation genetic diagnosis (PGD)-PCR procedure and to determine the diagnostic value. Genotyped embryos not selected for embryo transfer (ET) and unsuitable for cryopreservation after PGD were used for confirmatory analysis. The PGD genotyped blastomeres and corresponding embryos were compared, and morphology was scored on Day 4 post fertilization. To establish the validity of the PGD-PCR procedure and the diagnostic value, misdiagnosis rate, false-negative rate and negative predictive value were calculated. Moreover, comparison on the validity was made for the biopsy of one or two blastomeres. For the total embryo group (n = 422), a misdiagnosis rate of 7.1% and a false-negative rate of 3.1% were found. The negative predictive value was 96.1%. Poor morphology Day 4 embryos (Class 1) were over-represented in the embryo group in which the blastomere genotype was not confirmed by the whole embryo genotype. The misdiagnosis rate of Class 1 embryos was 12.5% and the false-negative rate 17.1%. Exclusion of these embryos resulted in a misdiagnosis rate of 6.1%, a false-negative rate of 0.5% and a negative predictive value of 99.3%. The two blastomere biopsies revealed a significant higher positive predictive value, lowering the misdiagnosis rate, whereas the negative predictive value remained the same. In conclusion, the PGD-PCR procedure is a valid diagnostic method to select unaffected embryos for ET. The misdiagnosis and false-negative rates decrease by rejecting Class 1 embryos for ET. The biopsy of a second blastomere improves the positive predictive value, lowering the misdiagnosis rate.

Analysis of segregation patterns in Machado-Joseph disease pedigrees

Machado-Joseph disease (MJD), also known as spinocerebellar ataxia type 3 (SCA3), is an autosomal dominant neurodegenerative disorder of late onset, which is considered the most common form of SCA worldwide. The main goal of this study was to investigate the presence of segregation ratio distortion (SRD) during transmissions of ATXN3 alleles by MJD patients, evaluating the putative role of SRD in the epidemiological representation of the disease. Sixty-two complete sibships, each with one clinically affected parent, totalling 330 transmissions were selected according to defined criteria and used for segregation analysis. Onset data from MJD patients with Azorean origin was used for residual risk estimates according to different ages. Residual risk values were applied to unaffected offspring to calculate the probability of inheriting the expanded allele. The proportion of offspring that received the expanded or the normal allele from the affected parent was calculated to determine the presence of SRD during transmissions of ATXN3 alleles by MJD patients. Segregation of ATXN3 alleles was in accordance with the expected Mendelian proportions (chi (2) = 0.982, P = 0.322). However, there was a tendency favouring the transmission of the normal alleles. Thus, SRD is not a potential mechanism on the basis of MJD epidemiological representation.

Birth after pre-implantation genetic diagnosis (PGD) of spinocerebellar ataxia 2 (Sca2)

BACKGROUND

Spinocerebellar ataxia 2 (SCA2) is an autosomal-dominant neurodegenerative disease caused by an extended polyglutamine sequence in the ATXN2 protein. We describe the development of a new single-cell multiplex PCR protocol for pre-implantation genetic diagnosis (PGD) of SCA2 and its successful clinical application.

METHODS

Three duplex tests have been developed, one, which combines the detection of the CAG repeats in addition to the D12S821 microsatellite, another, the amplification of the CAG repeats and the D12S1333 microsatellite and the last, the combination of both microsatellites D12S821 and D12S1333.

RESULTS

PCR conditions were established using 226 single lymphoblasts or patient lymphocysts. Amplification was obtained in an average of 99.6%, a complete genotype in 86%, a conclusive result in 96% and an allelic drop-out (ADO) rate of 10.7% was observed. PGD for SCA2 was performed for a couple with a paternal risk of transmitting the pathology. Two cycles were done from which 18 embryos were biopsied, 8 were diagnosed as unaffected, 9 as affected and 1 gave no results. In both cycles 2 embryos were transferred, with no pregnancy at the first attempt, and a twin pregnancy at the second attempt. The patient delivered one girl and one boy at 36 weeks and 3 days.

Preimplantation genetic diagnosis for myotonic dystrophy type 1: detection of crossover between the gene and the linked marker APOC2

OBJECTIVE

To report two cases of preimplantation genetic diagnosis (PGD) for myotonic dystrophy type I (DM1) where cross-over between the DMPK locus and a linked polymorphic marker APOC2 was detected.

METHODS

Embryos from in vitro fertilisation (IVF) were biopsied at day 3 of development and single blastomeres collected. Diagnosis was performed by duplex or triplex fluorescent-polymerase chain reaction (F-PCR) to amplify DMPK and APOC2 loci, or DMPK with APOC2 and D19S112 polymorphic markers.

RESULTS

A total of 22 oocytes were retrieved from the two patients, 20 were inseminated of which 15 fertilized (75%) and were suitable for biopsy on day 3. A diagnosis was obtained for 12 embryos (80%) and was confirmed in all un-transferred embryos. Crossover between DM1 and APOC2 was detected in two embryos from the two different couples. Transfer of two embryos took place in both cases resulting in two pregnancies. Each couple have had a healthy baby.

CONCLUSION

The above cases highlight the importance of using more than one linked polymorphic marker in PGD-PCR protocols and emphasize the danger of using APOC2 as the sole marker to identify the DM1 mutation.

Preimplantation genetic diagnosis

This article covers the rapidly advancing field of preimplantation genetic diagnosis (PGD), the molecular genetic analysis of cells taken from embryos formed through in vitro fertilization (IVF). The article focuses on current practices in patient management, relevant IVF and PGD procedures, molecular methods used in the genetic analysis, and technical difficulties that can affect test results. It discusses the growing list of indications for PGD including chromosomal disorders, monogenic disorders and human leukocyte antigen typing typing of embryos. The article also examines some of the emerging technologies being introduced into PGD.