Stephanie Efthymiou

PRUNE is crucial for normal brain development and mutated in microcephaly with neurodevelopmental impairment

Zollo et al. report that mutations in PRUNE1, a phosphoesterase superfamily molecule, underlie primary microcephaly and profound global developmental delay in four unrelated families from Oman, India, Iran and Italy. The study highlights a potential role for prune during microtubule polymerization, suggesting that prune syndrome may be a tubulinopathy.

Homozygous Mutations in VAMP1 Cause a Presynaptic Congenital Myasthenic Syndrome

We report 2 families with undiagnosed recessive presynaptic congenital myasthenic syndrome (CMS). Whole exome or genome sequencing identified segregating homozygous variants in VAMP1: c.51_64delAGGTGGGGGTCCCC in a Kuwaiti family and c.146G>C in an Israeli family. VAMP1 is crucial for vesicle fusion at presynaptic neuromuscular junction (NMJ). Electrodiagnostic examination showed severely low compound muscle action potentials and presynaptic impairment. We assessed the effect of the nonsense mutation on mRNA levels and evaluated the NMJ transmission in VAMP1lew/lew mice, observing neurophysiological features of presynaptic impairment, similar to the patients. Taken together, our findings highlight VAMP1 homozygous mutations as a cause of presynaptic CMS. Ann Neurol 2017;81:597–603

The phenotypic and molecular spectrum of PEHO syndrome and PEHO-like disorders

1 Department of Molecular Neuroscience, Institute of Neurology, UCL Institute of Neurology, London WC1N 3BG, UK 2 Department of Molecular Medicine and Medical Biotechnologies “DMMBM”, University of Naples “Federico II”, Naples 80131, Italy 3 CEINGE Biotecnologie Avanzate, Naples 80131, Italy 4 European School of Molecular Medicine, SEMM, University of Milan, Italy 5 King Saud bin Abdulaziz University for Health Sciences, Department of Pediatrics, Division of Genetics, Riyadh 14611, Saudi Arabia 6 Genetics and Rare Diseases Research Division, Ospedale Pediatrico “Bambino Gesù”, Rome 00146, Italy

Mutations in NKX6-2 Cause Progressive Spastic Ataxia and Hypomyelination.

Progressive limb spasticity and cerebellar ataxia are frequently found together in clinical practice and form a heterogeneous group of degenerative disorders that are classified either as pure spastic ataxia or as complex spastic ataxia with additional neurological signs. Inheritance is either autosomal dominant or autosomal recessive. Hypomyelinating features on MRI are sometimes seen with spastic ataxia, but this is usually mild in adults and severe and life limiting in children. We report seven individuals with an early-onset spastic-ataxia phenotype. The individuals come from three families of different ethnic backgrounds. Affected members of two families had childhood onset disease with very slow progression. They are still alive in their 30s and 40s and show predominant ataxia and cerebellar atrophy features on imaging. Affected members of the third family had a similar but earlier-onset presentation associated with brain hypomyelination. Using a combination of homozygozity mapping and exome sequencing, we mapped this phenotype to deleterious nonsense or homeobox domain missense mutations in NKX6-2. NKX6-2 encodes a transcriptional repressor with early high general and late focused CNS expression. Deficiency of its mouse ortholog results in widespread hypomyelination in the brain and optic nerve, as well as in poor motor coordination in a pattern consistent with the observed human phenotype. In-silico analysis of human brain expression and network data provides evidence that NKX6-2 is involved in oligodendrocyte maturation and might act within the same pathways of genes already associated with central hypomyelination. Our results support a non-redundant developmental role of NKX6-2 in humans and imply that NKX6-2 mutations should be considered in the differential diagnosis of spastic ataxia and hypomyelination.

Genotype-phenotype correlations and expansion of the molecular spectrum of AP4M1-related hereditary spastic paraplegia

BackgroundAutosomal recessive hereditary spastic paraplegia (HSP) due to AP4M1 mutations is a very rare neurodevelopmental disorder reported for only a few patients.MethodsWe investigated a Greek HSP family using whole exome sequencing (WES).ResultsA novel AP4M1A frameshift insertion, and a very rare missense variant were identified in all three affected siblings in the compound heterozygous state (p.V174fs and p.C319R); the unaffected parents were carriers of only one variant. Patients were affected with a combination of: (a) febrile seizures with onset in the first year of life (followed by epileptic non-febrile seizures); (b) distinctive facial appearance (e.g., coarse features, bulbous nose and hypomimia); (c) developmental delay and intellectual disability; (d) early-onset spastic weakness of the lower limbs; and (e) cerebellar hypoplasia/atrophy on brain MRI.ConclusionsWe review genotype-phenotype correlations and discuss clinical overlaps between different AP4-related diseases. The AP4M1 belongs to a complex that mediates vesicle trafficking of glutamate receptors, being likely involved in brain development and neurotransmission.

Next-generation sequencing in neuromuscular diseases.

PURPOSE OF REVIEW Neuromuscular diseases are clinically and genetically heterogeneous and probably contain the greatest proportion of causative Mendelian defects than any other group of conditions. These disorders affect muscle and/or nerves with neonatal, childhood or adulthood onset, with significant disability and early mortality. Along with heterogeneity, unidentified and often very large genes require complementary and comprehensive methods in routine molecular diagnosis. Inevitably, this leads to increased diagnostic delays and challenges in the interpretation of genetic variants. RECENT FINDINGS The application of next-generation sequencing, as a research and diagnostic strategy, has made significant progress into solving many of these problems. The analysis of these data is by no means simple, and the clinical input is essential to interpret results. SUMMARY In this review, we describe using examples the recent advances in the genetic diagnosis of neuromuscular disorders, in research and clinical practice and the latest developments that are underway in next-generation sequencing. We also discuss the latest collaborative initiatives such as the Genomics England (Department of Health, UK) genome sequencing project that combine rare disease clinical phenotyping with genomics, with the aim of defining the vast majority of rare disease genes in patients as well as modifying risks and pharmacogenomics factors.

Genotype-phenotype correlations, dystonia and disease progression in spinocerebellar ataxia type 14

Background: Spinocerebellar ataxia type 14 is a rare form of autosomal dominant cerebellar ataxia caused by mutations in protein kinase Cγ gene. Clinically, it presents with a slowly progressive, mainly pure cerebellar ataxia.

A homozygous loss-of-function mutation in PDE2A associated to early-onset hereditary chorea: A Homozygous PDE2A Mutation Causing Chorea

Background: We investigated a family that presented with an infantile‐onset chorea‐predominant movement disorder, negative for NKX2‐1, ADCY5, and PDE10A mutations. Methods: Phenotypic characterization and trio whole‐exome sequencing was carried out in the family. Results: We identified a homozygous mutation affecting the GAF‐B domain of the 3’,5’‐cyclic nucleotide phosphodiesterase PDE2A gene (c.1439A>G; p.Asp480Gly) as the candidate novel genetic cause of chorea in the proband. PDE2A hydrolyzes cyclic adenosine/guanosine monophosphate and is highly expressed in striatal medium spiny neurons. We functionally characterized the p.Asp480Gly mutation and found that it severely decreases the enzymatic activity of PDE2A. In addition, we showed equivalent expression in human and mouse striatum of PDE2A and its homolog gene, PDE10A. Conclusions: We identified a loss‐of‐function homozygous mutation in PDE2A associated to early‐onset chorea. Our findings possibly strengthen the role of cyclic adenosine monophosphate and cyclic guanosine monophosphate metabolism in striatal medium spiny neurons as a crucial pathophysiological mechanism in hyperkinetic movement disorders.

Analysis of the prion protein gene in multiple system atrophy

Neurodegenerative diseases are a very diverse group of disorders but they share some common mechanisms such as abnormally misfolded proteins with prion-like propagation and aggregation. Creutzfeldt-Jakob disease (CJD) is the most prevalent prion disease in humans. In the sporadic form of CJD the only known risk factor is the codon 129 polymorphism. Recent reports suggested that α-synuclein in multiple system atrophy (MSA) has similar pathogenic mechanisms as the prion protein. Here we present 1 Italian family with MSA and prion disease. Also, cases of concurrent MSA and prion pathology in the same individual or family suggest the possibility of molecular interaction between prion protein and α-synuclein in the process of protein accumulation and neurodegeneration, warranting further investigations. We assessed the PRNP gene by whole-exome sequencing in 264 pathologically confirmed MSA cases and 462 healthy controls to determine whether the 2 diseases share similar risk factors. We then analyzed codon 129 polymorphism by Sanger sequencing and compared with previously published results in sporadic CJD. Homozygosity at codon 129 was present in 50% of pathologically confirmed MSA cases and in 58% of normal controls (odds ratio, 0.7 (95% confidence interval of 0.5–0.9)) compared with 88.2% in sporadic CJD. Our data show that the homozygous state of position 129 in the PRNP is not a risk factor for MSA. No other variants in the PRNP gene were associated with increased risk for MSA.

PDE10A and ADCY5 mutations linked to molecular and microstructural basal ganglia pathology: PDE10A and ADCY5 Mutations Pathology

Striatal cyclic adenosine monophosphate activity modulates movement and is determined from the balance between its synthesis by adenylate cyclase 5 (ADCY5) and its degradation by phosphodiesterase 10A (PDE10A).