Progressive Myoclonus Epilepsy in Congenital Generalized Lipodystrophy type 2: Report of 3 cases and literature review

PURPOSE

A small case series with a neurodegenerative disorder involving central nervous system and related to Seipin mutations was recently reported. Herein we describe clinical and EEG features of three patients presenting with Progressive Myoclonus Epilepsy (PME) and Congenital Generalized Lipodystrophy type 2 (CGL2) related to novel Seipin mutations.

METHODS

The EEG-clinical picture was evaluated at epilepsy onset and in the follow-up period. The molecular analysis of BSCL2, Laforin and Malin genes was performed to patients and/or their parents by Denaturing High Performance Liquid Chromatography and automated nucleotide sequencing. Skin specimens collected from a patient were processed for histochemical and ultrastructural analysis.

RESULTS

The CGL2-PME syndrome co-segregated with two different BSCL2 genotypes: the homozygosity for c.782_783dupG involving exon 8 (two cases), or the compound heterozygosity for c.782_783dupG/c.828_829delAA (one case). Periodic-Acid Schiff positive osmiophilic material in the cytoplasm of fibrocytes and eccrine-gland cells were found in skin specimens. The lack of Lafora's bodies in skin specimens and the molecular analysis excluding mutations in Laforin and Malin genes ruled out Lafora disease.

CONCLUSION

The spectrum of CGL2 associated to BSCL2 gene mutations may include PMEs. Selected mutations in BSCL2 gene seem to be related to PMEs in patients with CGL2 phenotype.

Proteomic Profiling in the Brain of CLN1 Disease Model Reveals Affected Functional Modules

Neuronal ceroid lipofuscinoses (NCL) are the most commonly inherited progressive encephalopathies of childhood. Pathologically, they are characterized by endolysosomal storage with different ultrastructural features and biochemical compositions. The molecular mechanisms causing progressive neurodegeneration and common molecular pathways linking expression of different NCL genes are largely unknown. We analyzed proteome alterations in the brains of a mouse model of human infantile CLN1 disease-palmitoyl-protein thioesterase 1 (Ppt1) gene knockout and its wild-type age-matched counterpart at different stages: pre-symptomatic, symptomatic and advanced. For this purpose, we utilized a combination of laser capture microdissection-based quantitative liquid chromatography tandem mass spectrometry (MS) and matrix-assisted laser desorption/ionization time-of-flight MS imaging to quantify/visualize the changes in protein expression in disease-affected brain thalamus and cerebral cortex tissue slices, respectively. Proteomic profiling of the pre-symptomatic stage thalamus revealed alterations mostly in metabolic processes and inhibition of various neuronal functions, i.e., neuritogenesis. Down-regulation in dynamics associated with growth of plasma projections and cellular protrusions was further corroborated by findings from RNA sequencing of CLN1 patients' fibroblasts. Changes detected at the symptomatic stage included: mitochondrial functions, synaptic vesicle transport, myelin proteome and signaling cascades, such as RhoA signaling. Considerable dysregulation of processes related to mitochondrial cell death, RhoA/Huntington's disease signaling and myelin sheath breakdown were observed at the advanced stage of the disease. The identified changes in protein levels were further substantiated by bioinformatics and network approaches, immunohistochemistry on brain tissues and literature knowledge, thus identifying various functional modules affected in the CLN1 childhood encephalopathy.

Proteomic analysis of the palmitoyl protein thioesterase 1 interactome in SH-SY5Y human neuroblastoma cells

Neuronal ceroid lipofuscinoses (NCL) are a group of inherited progressive childhood disorders, characterized by early accumulation of autofluorescent storage material in lysosomes of neurons or other cells. Clinical symptoms of NCL include: progressive loss of vision, mental and motor deterioration, epileptic seizures and premature death. CLN1 disease (MIM#256730) is caused by mutations in the CLN1 gene, which encodes palmitoyl protein thioesterase 1 (PPT1). In this study, we utilised single step affinity purification coupled to mass spectrometry (AP-MS) to unravel the in vivo substrates of human PPT1 in the brain neuronal cells. Protein complexes were isolated from human PPT1 expressing SH-SY5Y stable cells, subjected to filter-aided sample preparation (FASP) and analysed on a Q Exactive Hybrid Quadrupole-Orbitrap mass spectrometer. A total of 23 PPT1 interacting partners (IP) were identified from label free quantitation of the MS data by SAINT platform. Three of the identified PPT1 IP, namely CRMP1, DBH, and MAP1B are predicted to be palmitoylated. Our proteomic analysis confirmed previously suggested roles of PPT1 in axon guidance and lipid metabolism, yet implicates the enzyme in novel roles including: involvement in neuronal migration and dopamine receptor mediated signalling pathway.

BIOLOGICAL SIGNIFICANCE

The significance of this work lies in the unravelling of putative in vivo substrates of human CLN1 or PPT1 in brain neuronal cells. Moreover, the PPT1 IP implicate the enzyme in novel roles including: involvement in neuronal migration and dopamine receptor mediated signalling pathway.

MECP2 duplication phenotype in symptomatic females: report of three further cases

Background

Xq28 duplications, including MECP2 (methyl CpG-binding protein 2; OMIM 300005), have been identified in approximately 140 male patients presenting with hypotonia, severe developmental delay/intellectual disability, limited or absent speech and ambulation, and recurrent respiratory infections. Female patients with Xq28 duplication have been rarely reported and are usually asymptomatic. Altogether, only fifteen symptomatic females with Xq28 duplications including MECP2 have been reported so far: six of them had interstitial duplications while the remaining had a duplication due to an unbalanced X;autosome translocation. Some of these females present with unspecific mild to moderate intellectual disability whereas a more complex phenotype is reported for females with unbalanced X;autosome translocations.

Findings

Here we report on the clinical features of three other adolescent to adult female patients with Xq28 interstitial duplications of variable size, all including MECP2 gene.

Conclusions

Mild to moderate cognitive impairment together with learning difficulties and speech delay were evident in each of our patients. Moreover, early inadequate behavioral patterns followed by persistent difficulties in the social and communication domains, as well as the occurrence of mild psychiatric disturbances, are common features of these three patients.

NCL diseases - clinical perspectives

The neuronal ceroid lipofuscinoses (NCLs) are lysosomal storage disorders and together are the most common degenerative brain diseases in childhood. They are a group of disorders linked by the characteristic accumulation of abnormal storage material in neurons and other cell types, and a degenerative disease course. All NCLs are characterized by a combination of dementia, epilepsy, and motor decline. For most childhood NCLs, a progressive visual failure is also a core feature. The characteristics of these symptoms can vary and the age at disease onset ranges from birth to young adulthood. Genetic heterogeneity, with fourteen identified NCL genes and wide phenotypic variability render diagnosis difficult. A new NCL classification system based on the affected gene and the age at disease onset allows a precise and practical delineation of an individual patient's NCL type. A diagnostic algorithm to identify each NCL form is presented here. Precise NCL diagnosis is essential not only for genetic counseling, but also for the optimal delivery of care and information sharing with the family and other caregivers. These aspects are challenging because there are also potential long term complications which are specific to NCL type. Therefore care supported by a specifically experienced team of clinicians is recommended. As the underlying pathophysiological mechanism is still unclear for all NCL forms, the development of curative therapies remains difficult. This article is part of a Special Issue entitled: The neuronal ceroid lipofuscinoses or Batten Disease.

Molecular epidemiology of childhood neuronal ceroid-lipofuscinosis in Italy

Background

To review the descriptive epidemiological data on neuronal ceroid lipofuscinoses (NCLs) in Italy, identify the spectrum of mutations in the causative genes, and analyze possible genotype-phenotype relations.

Methods

A cohort of NCL patients was recruited through CLNet, a nationwide network of child neurology units. Diagnosis was based on clinical and pathological criteria following ultrastructural investigation of peripheral tissues. Molecular confirmation was obtained during the diagnostic procedure or, when possible, retrospectively.

Results

One hundred eighty-three NCL patients from 156 families were recruited between 1966 and 2010; 124 of these patients (from 88 families) were tested for known NCL genes, with 9.7% of the patients in this sample having not a genetic diagnosis. Late infantile onset NCL (LINCL) accounted for 75.8% of molecularly confirmed cases, the most frequent form being secondary to mutations in CLN2 (23.5%). Juvenile onset NCL patients accounted for 17.7% of this cohort, a smaller proportion than found in other European countries. Gene mutations predicted severe protein alterations in 65.5% of the CLN2 and 78.6% of the CLN7 cases. An incidence rate of 0.98/100,000 live births was found in 69 NCL patients born between 1992 and 2004, predicting 5 new cases a year. Prevalence was 1.2/1,000,000.

Conclusions

Descriptive epidemiology data indicate a lower incidence of NCLs in Italy as compared to other European countries. A relatively high number of private mutations affecting all NCL genes might explain the genetic heterogeneity. Specific gene mutations were associated with severe clinical courses in selected NCL forms only.

C19orf12 and FA2H mutations are rare in Italian patients with neurodegeneration with brain iron accumulation

Neurodegeneration with brain iron accumulation (NBIA) defines a wide spectrum of clinical entities characterized by iron accumulation in specific regions of the brain, predominantly in the basal ganglia. We evaluated the presence of FA2H and C19orf12 mutations in a cohort of 46 Italian patients with early onset NBIA, which were negative for mutations in the PANK2 and PLA2G6 genes. Follow-up molecular genetic and in vitro analyses were then performed. We did not find any mutations in the FA2H gene, although we identified 3 patients carrying novel mutations in the C19orf12 gene. The recent discovery of new genes responsible for NBIA extends the spectrum of the genetic investigation now available for these disorders and makes it possible to delineate a clearer clinical-genetic classification of different forms of this syndrome. A large fraction of patients still remain without a molecular genetics diagnosis, suggesting that additional NBIA genes are still to be discovered.

Ataxia in mitochondrial disorders

Mitochondria are subcellular organelles whose major function is to generate energy by coupling through oxidation of nutrient substrates with ATP synthesis, via ADP phosphorylation. This process, known as oxidative phosphorylation, is carried out by the mitochondrial respiratory chain, a pathway consisting of five multi-subunit complexes, four of which take contribution from genes located in two separate compartments, the nuclear chromosomes, and a genome found in mitochondria themselves, mitochondrial DNA (mtDNA). Defects affecting either genome give rise to mitochondrial dysfunction, causing disease that often affects the brain and in particular the cerebellum. Mitochondrial disorders can give rise to pure cerebellar, spinocerebellar, or sensory ataxia, usually as part of a multisystem (and multisymptom) disorder. In this chapter we divide the diseases into those caused by mtDNA defects and those due to mutations involving nuclear genes. With more than 100 mutations in mtDNA and new nuclear genes being described all the time, we have focused on the commonest disorders and used these as examples of the different types of mitochondrial ataxia.

Involvement of the mitochondrial compartment in human NCL fibroblasts

Neuronal ceroid lipofuscinosis (NCL) are a group of progressive neurodegenerative disorders of childhood, characterized by the endo-lysosomal storage of autofluorescent material. Impaired mitochondrial function is often associated with neurodegeneration, possibly related to the apoptotic cascade. In this study we investigated the possible effects of lysosomal accumulation on the mitochondrial compartment in the fibroblasts of two NCL forms, CLN1 and CLN6. Fragmented mitochondrial reticulum was observed in all cells by using the intravital fluorescent marker Mitotracker, mainly in the perinuclear region. This was also associated with intense signal from the lysosomal markers Lysotracker and LAMP2. Likewise, mitochondria appeared to be reduced in number and shifted to the cell periphery by electron microscopy; moreover the mitochondrial markers VDCA and COX IV were reduced following quantitative Western blot analysis. Whilst there was no evidence of increased cell death under basal condition, we observed a significant increase in apoptotic nuclei following Staurosporine treatment in CLN1 cells only. In conclusion, the mitochondrial compartment is affected in NCL fibroblasts invitro, and CLN1 cells seem to be more vulnerable to the negative effects of stressed mitochondrial membrane than CLN6 cells.

Molecular genetic analysis of the PLP1 gene in 38 families with PLP1-related disorders: identification and functional characterization of 11 novel PLP1 mutations

Background

The breadth of the clinical spectrum underlying Pelizaeus-Merzbacher disease and spastic paraplegia type 2 is due to the extensive allelic heterogeneity in the X-linked PLP1 gene encoding myelin proteolipid protein (PLP). PLP1 mutations range from gene duplications of variable size found in 60-70% of patients to intragenic lesions present in 15-20% of patients.

Methods

Forty-eight male patients from 38 unrelated families with a PLP1-related disorder were studied. All DNA samples were screened for PLP1 gene duplications using real-time PCR. PLP1 gene sequencing analysis was performed on patients negative for the duplication. The mutational status of all 14 potential carrier mothers of the familial PLP1 gene mutation was determined as well as 15/24 potential carrier mothers of the PLP1 duplication.

Results and Conclusions

PLP1 gene duplications were identified in 24 of the unrelated patients whereas a variety of intragenic PLP1 mutations were found in the remaining 14 patients. Of the 14 different intragenic lesions, 11 were novel; these included one nonsense and 7 missense mutations, a 657-bp deletion, a microdeletion and a microduplication. The functional significance of the novel PLP1 missense mutations, all occurring at evolutionarily conserved residues, was analysed by the MutPred tool whereas their potential effect on splicing was ascertained using the Skippy algorithm and a neural network. Although MutPred predicted that all 7 novel missense mutations would be likely to be deleterious, in silico analysis indicated that four of them (p.Leu146Val, p.Leu159Pro, p.Thr230Ile, p.Ala247Asp) might cause exon skipping by altering exonic splicing elements. These predictions were then investigated in vitro for both p.Leu146Val and p.Thr230Ile by means of RNA or minigene studies and were subsequently confirmed in the case of p.Leu146Val. Peripheral neuropathy was noted in four patients harbouring intragenic mutations that altered RNA processing, but was absent from all PLP1-duplication patients. Unprecedentedly, family studies revealed the de novo occurrence of the PLP1 duplication at a frequency of 20%.

Pontocerebellar hypoplasia: clinical, pathologic, and genetic studies

BACKGROUND

Mutations in genes encoding subunits of the tRNA-splicing endonuclease (TSEN) complex were identified in patients with pontocerebellar hypoplasia 2 (PCH2) and pontocerebellar hypoplasia 4 (PCH4).

OBJECTIVE

We report molecular genetic findings in 12 Italian patients with clinical and MRI findings compatible with PCH2 and PCH4.

METHODS

We retrospectively selected a cohort of 12 children from 9 Italian families with MRI of hypoplastic pontocerebellar structures and clinical manifestations suggesting either PCH2 or PCH4 and submitted them to direct sequencing of the genes encoding the 4 subunits of the TSEN complex, namely TSEN54, TSEN34, TSEN15, and TSEN2.

RESULTS

In a cohort of 12 children, we detected the common p.A307S mutation in TSEN54 in 9/12 available patients from nine unrelated families. We also detected a novel c.1170_1183del (p. V390fs39X) in compound heterozygosity with the common p.A307S in a child with a severe PCH4 phenotype. In another severely affected patient, the second mutant allele was not identified. Two sibs without mutations in the TSEN complex were unlinked to the PCH3 locus. In addition to typical clinical and neuroradiologic features of PCH2, both children were affected by a tubulopathy resembling Bartter syndrome.

CONCLUSIONS

We confirm that the common p.A307S mutation in TSEN54 is responsible for most of the patients with a PCH2 phenotype. The presence of a heterozygous in/del variant correlates with a more severe phenotype as PCH4. In addition, we describe a new clinical form of PCH in 2 sibs with clinical and MRI features of PCH2.

Expanding CEP290 mutational spectrum in ciliopathies

Ciliopathies are an expanding group of rare conditions characterized by multiorgan involvement, that are caused by mutations in genes encoding for proteins of the primary cilium or its apparatus. Among these genes, CEP290 bears an intriguing allelic spectrum, being commonly mutated in Joubert syndrome and related disorders (JSRD), Meckel syndrome (MKS), Senior-Loken syndrome and isolated Leber congenital amaurosis (LCA). Although these conditions are recessively inherited, in a subset of patients only one CEP290 mutation could be detected. To assess whether genomic rearrangements involving the CEP290 gene could represent a possible mutational mechanism in these cases, exon dosage analysis on genomic DNA was performed in two groups of CEP290 heterozygous patients, including five JSRD/MKS cases and four LCA, respectively. In one JSRD patient, we identified a large heterozygous deletion encompassing CEP290 C-terminus that resulted in marked reduction of mRNA expression. No copy number alterations were identified in the remaining probands. The present work expands the CEP290 genotypic spectrum to include multiexon deletions. Although this mechanism does not appear to be frequent, screening for genomic rearrangements should be considered in patients in whom a single CEP290 mutated allele was identified.

Friedreich's ataxia: oxidative stress and cytoskeletal abnormalities

Friedreich's ataxia (FRDA) is an autosomal recessive disorder caused by mutations in the gene encoding frataxin, a mitochondrial protein implicated in iron metabolism. Current evidence suggests that loss of frataxin causes iron overload in tissues, and increase in free-radical production leading to oxidation and inactivation of mitochondrial respiratory chain enzymes, particularly Complexes I, II, III and aconitase. Glutathione plays an important role in the detoxification of ROS in the Central Nervous System (CNS), where it also provides regulation of protein function by glutathionylation. The cytoskeletal proteins are particularly susceptible to oxidation and appear constitutively glutathionylated in the human CNS. Previously, we showed loss of cytoskeletal organization in fibroblasts of patients with FRDA found to be associated with increased levels of glutathione bound to cytoskeletal proteins. In this study, we analysed the glutathionylation of proteins in the spinal cord of patients with FRDA and the distribution of tubulin and neurofilaments in the same area. We found, for the first time, a significant rise of the dynamic pool of tubulin as well as abnormal distribution of the phosphorylated forms of human neurofilaments in FRDA motor neurons. In the same cells, the cytoskeletal abnormalities co-localized with an increase in protein glutathionylation and the mitochondrial proteins were normally expressed by immunocytochemistry. Our results suggest that in FRDA oxidative stress causes abnormally increased protein glutathionylation leading to prominent abnormalities of the neuronal cytoskeleton.

Neuronal ceroid lipofuscinoses: many players, and more to come

The neuronal ceroid lipofuscinoses (NCL) are the most common group of progressive neurodegenerative diseases of childhood. The overall clinical features are highly similar regardless of the age at disease manifestation, the extent and shape of abnormally stored cytosomes and the severity of clinical course, and are generally characterized by failure and regression of psychomotor development, impaired vision, seizures and fatal outcome. The expanding array of genetic etiologies and disease-associated mutations in NCL provide the basis for the heterogeneity of these clinical conditions and are the focus of this review. Less understood are the pathogenic mechanisms, but common themes and molecular pathways are now emerging and new players are expected to come into the scene of NCL.

Screening of ARHSP-TCC patients expands the spectrum of SPG11 mutations and includes a large scale gene deletion

Autosomal recessive spastic paraplegia with thinning of corpus callosum (ARHSP-TCC) is a complex form of HSP initially described in Japan but subsequently reported to have a worldwide distribution with a particular high frequency in multiple families from the Mediterranean basin. We recently showed that ARHSP-TCC is commonly associated with mutations in SPG11/KIAA1840 on chromosome 15q. We have now screened a collection of new patients mainly originating from Italy and Brazil, in order to further ascertain the spectrum of mutations in SPG11, enlarge the ethnic origin of SPG11 patients, determine the relative frequency at the level of single Countries (i.e., Italy), and establish whether there is one or more common mutation. In 25 index cases we identified 32 mutations; 22 are novel, including 9 nonsense, 3 small deletions, 4 insertions, 1 in/del, 1 small duplication, 1 missense, 2 splice-site, and for the first time a large genomic rearrangement. This brings the total number of SPG11 mutated patients in the SPATAX collection to 111 cases in 44 families and in 17 isolated cases, from 16 Countries, all assessed using homogeneous clinical criteria. While expanding the spectrum of mutations in SPG11, this larger series also corroborated the notion that even within apparently homogeneous population a molecular diagnosis cannot be achieved without full gene sequencing.

Mutations in MFSD8/CLN7 are a frequent cause of variant-late infantile neuronal ceroid lipofuscinosis

The neuronal ceroid lipofuscinoses (NCL) are a group of genetically heterogeneous neurodegenerative disorders. The recent identification of the MFSD8/CLN7 gene in a variant-late infantile form of NCL (v-LINCL) in affected children from Turkey prompted us to examine the relative frequency of variants in this gene in Italian patients with v-LINCL. We identified nine children harboring 11 different mutations in MFSD8/CLN7. Ten mutations were novel and included three nonsense (p.Arg35Stop, p.Glu381Stop, p.Arg482Stop), four missense (p.Met1Thr, p.Gly52Arg, p.Thr294Lys, p.Pro447Leu), two splice site mutations (c.863+3_4insT, c.863+1G>C), and a 17-bp deletion predicting a frameshift and premature protein truncation (c.627_643del17/p.Met209IlefsX3). The clinical phenotype, which was similar to that of the Turkish v-LINCL cases, was not influenced by type and location of the mutation nor the length of the predicted residual gene product. As well as identifying novel variants in MFSD8/CLN7, this study contributes to a better molecular characterization of Italian NCL cases, and will facilitate medical genetic counseling in such families. The existence of a subset of v-LINCL cases without mutations in any of the known NCL genes suggests further genetic heterogeneity.

Variant late infantile neuronal ceroid lipofuscinosis because of CLN1 mutations

The neuronal ceroid lipofuscinoses are a heterogeneous group of inherited degenerative disorders of the central nervous system. Cases of ceroid lipofuscinosis with cytoplasmic storage of granular osmiophilic deposits are associated with reduced activity of palmitoyl-protein thioesterase-1 (PPT-1) and mutations in CLN1, and occur from infancy to adulthood. We present clinical and diagnostic investigations in six children with variant late infantile neuronal ceroid lipofuscinosis and mutations in CLN1. The main clinical features at onset were behavioral disturbances and cognitive decline. Myoclonic jerks constituted the most prominent paroxysmal phenomenon. An electroencephalogram revealed the "vanishing" pattern described in infantile ceroid lipofuscinosis. Neurologic regression was associated with dramatic shrinkage of cortical structures, evident upon brain magnetic resonance imaging. Three unrelated children harboring the same homozygous mutation in CLN1 and a girl who carried a novel mutation resulting in skipping of multiple exons presented with a similar clinical phenotype. The most severe picture occurred in two siblings who carried a homozygous mutation predicting a prematurely truncated protein. Similar to the infantile form, the clinical evolution in this group of patients was characterized by an onset of severe neurologic impairment, peaking within a relatively short period of time, followed by a slower evolution of the disease.

Neurodegeneration associated with genetic defects in phospholipase A(2)

OBJECTIVE

Mutations in the gene encoding phospholipase A(2) group VI (PLA2G6) are associated with two childhood neurologic disorders: infantile neuroaxonal dystrophy (INAD) and idiopathic neurodegeneration with brain iron accumulation (NBIA). INAD is a severe progressive psychomotor disorder in which axonal spheroids are found in brain, spinal cord, and peripheral nerves. High globus pallidus iron is an inconsistent feature of INAD; however, it is a diagnostic criterion of NBIA, which describes a clinically and genetically heterogeneous group of disorders that share this hallmark feature. We sought to delineate the clinical, radiographic, pathologic, and genetic features of disease resulting from defective phospholipase A(2).

METHODS

We identified 56 patients clinically diagnosed with INAD and 23 with idiopathic NBIA and screened their DNA for PLA2G6 mutations.

RESULTS

Eighty percent of patients with INAD had mutations in PLA2G6, whereas mutations were found in only 20% of those with idiopathic NBIA. All patients with two null mutations had a more severe phenotype. On MRI, nearly all mutation-positive patients had cerebellar atrophy, and half showed brain iron accumulation. We observed Lewy bodies and neurofibrillary tangles in association with PLA2G6 mutations.

CONCLUSION

Defects in phospholipase A(2) lead to a range of phenotypes. PLA2G6 mutations are associated with nearly all cases of classic infantile neuroaxonal dystrophy but a minority of cases of idiopathic neurodegeneration with brain iron accumulation, and genotype correlates with phenotype. Cerebellar atrophy predicts which patients are likely to be mutation-positive. The neuropathologic changes that are caused by defective phospholipase A(2) suggest a shared pathogenesis with both Parkinson and Alzheimer diseases.