Genotype-Phenotype Relations for the Parkinson's Disease Genes Parkin, PINK1, DJ1: MDSGene Systematic Review.

This first comprehensive MDSGene review is devoted to the 3 autosomal recessive Parkinson's disease forms: PARK-Parkin, PARK-PINK1, and PARK-DJ1. It followed MDSGene's standardized data extraction protocol and screened a total of 3652 citations and is based on fully curated phenotypic and genotypic data on >1100 patients with recessively inherited PD because of 221 different disease-causing mutations in Parkin, PINK1, or DJ1. All these data are also available in an easily searchable online database (www.mdsgene.org), which also provides descriptive summary statistics on phenotypic and genetic data. Despite the high degree of missingness of phenotypic features and unsystematic reporting of genotype data in the original literature, the present review recapitulates many of the previously described findings including early onset (median age at onset of ∼30 years for carriers of at least 2 mutations in any of the 3 genes) of an overall clinically typical form of PD with excellent treatment response, dystonia and dyskinesia being relatively common and cognitive decline relatively uncommon. However, when comparing actual data with common expert knowledge in previously published reviews, we detected several discrepancies. We conclude that systematic reporting of phenotypes is a pressing need in light of increasingly available molecular genetic testing and the emergence of first gene-specific therapies entering clinical trials. © 2018 International Parkinson and Movement Disorder Society.

Facial twitches in ADCY5-associated disease - Myokymia or myoclonus? An electromyography study.

OBJECTIVE: A clinical feature in patients with ADCY5 gene mutations are perioral muscle twitches initially described as facial myokymia. METHODS: Five patients with ADCY5-associated disease with facial twitches and truncal jerks underwent electrophysiological investigations of the orbicularis oris and trapezius muscles to delineate neurophysiological characteristics of these phenomena. RESULTS: Electromyography (EMG) recordings showed a complex electrophysiological pattern with brief bursts of less than 100 ms and longer bursts with a duration of 100-300 ms up to several seconds in keeping with myoclonus and chorea, respectively, as key findings. None of the patients had EMG patterns of myokymia. CONCLUSIONS: In this series of five ADCY5 mutation carriers, perioral twitches and truncal jerks do not represent myokymia. In view of characteristic clinical signs and electrophysiological patterns with a combination of myoclonus and chorea it might be preferable to refer to these phenomena as myoclonus-chorea.

Novel GNB1 missense mutation in a patient with generalized dystonia, hypotonia, and intellectual disability.

Recently, exome sequencing has extended our knowledge of genetic causes of developmental delay through identification of de novo, germline mutations in the guanine nucleotide-binding protein, beta 1 (GNB1) in 13 patients with neurodevelopmental disability and a wide range of additional symptoms and signs including hypotonia in 11 and seizures in 10 of the patients. Limb/arm dystonia was found in 2 patients.(1).

Pitfalls in genetic testing: the story of missed SCN1A mutations.

BACKGROUND: Sanger sequencing, still the standard technique for genetic testing in most diagnostic laboratories and until recently widely used in research, is gradually being complemented by next-generation sequencing (NGS). No single mutation detection technique is however perfect in identifying all mutations. Therefore, we wondered to what extent inconsistencies between Sanger sequencing and NGS affect the molecular diagnosis of patients. Since mutations in SCN1A, the major gene implicated in epilepsy, are found in the majority of Dravet syndrome (DS) patients, we focused on missed SCN1A mutations. METHODS: We sent out a survey to 16 genetic centers performing SCN1A testing. RESULTS: We collected data on 28 mutations initially missed using Sanger sequencing. All patients were falsely reported as SCN1A mutation-negative, both due to technical limitations and human errors. CONCLUSION: We illustrate the pitfalls of Sanger sequencing and most importantly provide evidence that SCN1A mutations are an even more frequent cause of DS than already anticipated.

Investigating the genetic basis of fever-associated syndromic epilepsies using copy number variation analysis.

Fever-associated syndromic epilepsies ranging from febrile seizures plus (FS+) to Dravet syndrome have a significant genetic component. However, apart from SCN1A mutations in >80% of patients with Dravet syndrome, the genetic underpinnings of these epilepsies remain largely unknown. Therefore, we performed a genome-wide screening for copy number variations (CNVs) in 36 patients with SCN1A-negative fever-associated syndromic epilepsies. Phenotypes included Dravet syndrome (n = 23; 64%), genetic epilepsy with febrile seizures plus (GEFS+) and febrile seizures plus (FS+) (n = 11; 31%) and unclassified fever-associated epilepsies (n = 2; 6%). Array comparative genomic hybridization (CGH) was performed using Agilent 4 × 180K arrays. We identified 13 rare CNVs in 8 (22%) of 36 individuals. These included known pathogenic CNVs in 4 (11%) of 36 patients: a 1q21.1 duplication in a proband with Dravet syndrome, a 14q23.3 deletion in a proband with FS+, and two deletions at 16p11.2 and 1q44 in two individuals with fever-associated epilepsy with concomitant autism and/or intellectual disability. In addition, a 3q13.11 duplication in a patient with FS+ and two de novo duplications at 7p14.2 and 18q12.2 in a patient with atypical Dravet syndrome were classified as likely pathogenic. Six CNVs were of unknown significance. The identified genomic aberrations overlap with known neurodevelopmental disorders, suggesting that fever-associated epilepsy syndromes may be a recurrent clinical presentation of known microdeletion syndromes.

GABRA1 and STXBP1: novel genetic causes of Dravet syndrome.

OBJECTIVE: To determine the genes underlying Dravet syndrome in patients who do not have an SCN1A mutation on routine testing. METHODS: We performed whole-exome sequencing in 13 SCN1A-negative patients with Dravet syndrome and targeted resequencing in 67 additional patients to identify new genes for this disorder. RESULTS: We detected disease-causing mutations in 2 novel genes for Dravet syndrome, with mutations in GABRA1 in 4 cases and STXBP1 in 3. Furthermore, we identified 3 patients with previously undetected SCN1A mutations, suggesting that SCN1A mutations occur in even more than the currently accepted ∼ 75% of cases. CONCLUSIONS: We show that GABRA1 and STXBP1 make a significant contribution to Dravet syndrome after SCN1A abnormalities have been excluded. Our results have important implications for diagnostic testing, clinical management, and genetic counseling of patients with this devastating disorder and their families.

The unexpected role of copy number variations in juvenile myoclonic epilepsy.

Structural genomic variants or copy number variants (CNVs) comprise submicroscopic deletions and duplications of chromosomal material, including both rearrangements at genomic hotspots as well as duplications and deletions with unique breakpoints. Copy number variants have increasingly been recognized in the Idiopathic/Genetic Generalized Epilepsies (IGE/GGE) including juvenile myoclonic epilepsy (JME). Microdeletions at 15q13.3, 15q11.2, and 16p13.11 are genetic risk factors that can be identified in 3% of patients with IGE including JME. These microdeletions, however, also represent genetic risk factors to a broad range of other neurodevelopmental disorders. Additionally, 6% of patients with GGE carry other, potentially pathogenic structural genomic variants. While family studies largely support the channelopathy concept of the idiopathic epilepsies, the results of studies investigating copy number variations suggest that JME genetically overlaps with a broad range of other neurodevelopmental disorders. In addition, the particular genetic properties of structural genomic variations as rare genetic variants highlight the complexity of the genetic architecture of human disease.