Aromatic L-Amino Acid Decarboxylase Deficiency: A Genetic Screening in Sicilian Patients with Neurological Disorders

Aromatic L-amino acid decarboxylase deficiency (AADCd) is a rare autosomal recessive neurometabolic disorder caused by AADC deficiency, an enzyme encoded by the DDC gene. Since the enzyme is involved in the biosynthesis of serotonin and dopamine, its deficiency determines the lack of these neurotransmitters, but also of norepinephrine and epinephrine. Onset is early and the key signs are hypotonia, movement disorders (oculogyric crises, dystonia and hypokinesia), developmental delay and autonomic dysfunction. Taiwan is the site of a potential founder variant (IVS6+4A>T) with a predicted incidence of 1/32,000 births, while only 261 patients with this deficit have been described worldwide. Actually, the number of affected persons could be greater, given that the spectrum of clinical manifestations is broad and still little known. In our study we selected 350 unrelated patients presenting with different neurological disorders including heterogeneous neuromuscular disorders, cognitive deficit, behavioral disorders and autism spectrum disorder, for which the underlying etiology had not yet been identified. Molecular investigation of the DDC gene was carried out with the aim of identifying affected patients and/or carriers. Our study shows a high frequency of carriers (2.57%) in Sicilian subjects with neurological deficits, with a higher concentration in northern and eastern Sicily. Assuming these data as representative of the general Sicilian population, the risk may be comparable to some rare diseases included in the newborn screening programs such as spinal muscular atrophy, cystic fibrosis and phenylketonuria.

Genetic screening for hereditary transthyretin amyloidosis with polyneuropathy in western Sicily: Two years of experience in a neurological clinic

BACKGROUND AND PURPOSE

Hereditary transthyretin amyloidosis with polyneuropathy (ATTRv-PN) is caused by mutations in the TTR gene, leading to misfolded monomers that aggregate generating amyloid fibrils.

METHODS

A prospective systematic genetic screening for ATTRv-PN was proposed in patients presenting with a sensory-motor idiopathic polyneuropathy and two or more "red flags" among the following: family history of polyneuropathy or cardiopathy, bilateral carpal tunnel syndrome, cardiac insufficiency, renal amyloidosis, lumbar tract stenosis, autonomic dysfunction, idiopathic gastrointestinal disease, amyloid deposits on biopsy, and vitreous opacities. The detection rate was calculated, and nonparametric analyses were carried out to underline differences among screened positive versus negative patients.

RESULTS

In the first step, 145 suspected patients underwent genetic testing, revealing a diagnosis of ATTRv-PN in 14 patients (10%). Then, cascade screening allowed early recognition of 33 additional individuals (seven symptomatic ATTRv-PN patients and 26 presymptomatic carriers) among 84 first-degree relatives. Patients with a positive genetic test presented a higher frequency of unexplained weight loss, gastrointestinal symptoms, and family history of cardiopathy.

CONCLUSIONS

A systematic screening for ATTRv-PN yielded an increased recognition of the disease in our neurological clinic. Unexplained weight loss associated with axonal polyneuropathy had the highest predictive value in the guidance of clinical suspicion. A focused approach for the screening of ATTRv-PN could lead to an earlier diagnosis and identification of asymptomatic carriers, who will be promptly treated after a strict follow-up at the clinical onset.

The Y831C Mutation of the POLG Gene in Dementia

BACKGROUND

The POLG gene encodes the catalytic subunit of DNA polymerase γ, which is crucial for mitochondrial DNA (mtDNA) repair and replication. Gene mutation alters the stability of mtDNA and is associated with several clinical presentations, such as dysarthria and ophthalmoplegia (SANDO), progressive external ophthalmoplegia (PEO), spinocerebellar ataxia and epilepsy (SCAE), Alpers syndrome, and sensory ataxic neuropathy. Recent evidence has also indicated that POLG mutations may be involved in some neurodegenerative disorders, although systematic screening is currently lacking.

METHODS

To investigate the frequency of POLG gene mutations in neurodegenerative disorders, we screened a group of 33 patients affected by neurodegenerative diseases, including Parkinson's disease, some atypical parkinsonisms, and dementia of different types.

RESULTS

Mutational analysis revealed the presence of the heterozygous Y831C mutation in two patients, one with frontotemporal dementia and one with Lewy body dementia. The allele frequency of this mutation reported by the 1000 Genomes Project in the healthy population is 0.22%, while in our group of patients, it was 3.03%, thus showing a statistically significant difference between the two groups.

CONCLUSIONS

Our results may expand the genotype-phenotype spectrum associated with mutations in the POLG gene and strengthen the hypothesis of a pathogenic role of the Y831C mutation in neurodegeneration.

A novel compound heterozygous mutation in PYGM gene associated with McArdle's disease

McArdle's disease is an autosomal recessive glycogenosis due to mutation in the myophosphorylase gene (PYGM) resulting in a pure myopathy. The clinical onset typically occurs in childhood with cramps, myalgia, and intolerance to physical exercise, although late onset forms are also reported. We describe a case of a 17-year-old male complaining of cramps and myalgia following brief and intense exercise. The patient reported marked improvement in muscle fatigability few minutes after starting aerobic exercise. When he was a child, he had experienced few episodes of vomiting, nausea, and black colored urine following physical activity. Laboratory testings revealed high creatine kinase serum levels. Genetic testings for metabolic myopathies demonstrated a compound heterozygous for two PYGM mutations (p.R570Q and p.K754Nfs*49) allowing the diagnosis of McArdle's disease. To date, 183 mutations in the PYGM gene are listed in Human Gene Mutation Database Professional 2021.2, but this novel compound heterozygosis has never been reported before.

A Transcriptome Analysis of mRNAs and Long Non-Coding RNAs in Patients with Parkinson's Disease

Parkinson's disease (PD) is the second most common neurodegenerative disorder. The number of cases of PD is expected to double by 2030, representing a heavy burden on the healthcare system. Clinical symptoms include the progressive loss of dopaminergic neurons in the substantia nigra of the midbrain, which leads to striatal dopamine deficiency and, subsequently, causes motor dysfunction. Certainly, the study of the transcriptome of the various RNAs plays a crucial role in the study of this neurodegenerative disease. In fact, the aim of this study was to evaluate the transcriptome in a cohort of subjects with PD compared with a control cohort. In particular we focused on mRNAs and long non-coding RNAs (lncRNA), using the Illumina NextSeq 550 DX System. Differential expression analysis revealed 716 transcripts with padj ≤ 0.05; among these, 630 were mRNA (coding protein), lncRNA, and MT_tRNA. Ingenuity pathway analysis (IPA, Qiagen) was used to perform the functional and pathway analysis. The highest statistically significant pathways were: IL-15 signaling, B cell receptor signaling, systemic lupus erythematosus in B cell signaling pathway, communication between innate and adaptive immune cells, and melatonin degradation II. Our findings further reinforce the important roles of mitochondria and lncRNA in PD and, in parallel, further support the concept of inverse comorbidity between PD and some cancers.

mRNA expression profiling of mitochondrial subunits in subjects with Parkinson's disease

INTRODUCTION

Parkinson's disease (PD) is a common adult-onset neurodegenerative disorder caused by a progressive loss of dopaminergic neurons due to the accumulation of α-synuclein in the substantia nigra. Mitochondria are known to play a key role in cell respiratory function and bioenergetics. Indeed, mitochondrial dysfunction causes insufficient energy production required to satisfy the needs of several organs, especially the nervous system. However, the profiling of messenger RNA (mRNA) expression of mitochondrial subunits in PD has not been systematically investigated yet.

MATERIAL AND METHODS

We explored the mRNA expression of mitochondrial DNA (mtDNA) encoded respiratory chain (RC) subunits in 43 PD patients and 43 normal controls (NC). Next generation sequencing analysis (NGS) was used and quantitative real-time polymerase chain reaction (qRT-PCR) assay was used for confirmation of the NGS results.

RESULTS

All tested mitochondrial RC subunits were significantly over-expressed in subjects with PD compared to NC. In qRT-PCR the mean expression of all mitochondrial subunits had an expression level of at least 7 times compared to NC.

CONCLUSIONS

The over-expression of mitochondrial subunits in PD subjects with respect to NC might be secondary to a degeneration-related alteration of the mitochondrial structure and/or dynamics, or to the occurrence of a compensatory mechanism. The study of specific mRNA by peripheral blood mononuclear cells may provide a further diagnostic frame for early detection PD patients.

Bi-allelic JAM2 Variants Lead to Early-Onset Recessive Primary Familial Brain Calcification

Primary familial brain calcification (PFBC) is a rare neurodegenerative disorder characterized by a combination of neurological, psychiatric, and cognitive decline associated with calcium deposition on brain imaging. To date, mutations in five genes have been linked to PFBC. However, more than 50% of individuals affected by PFBC have no molecular diagnosis. We report four unrelated families presenting with initial learning difficulties and seizures and later psychiatric symptoms, cerebellar ataxia, extrapyramidal signs, and extensive calcifications on brain imaging. Through a combination of homozygosity mapping and exome sequencing, we mapped this phenotype to chromosome 21q21.3 and identified bi-allelic variants in JAM2. JAM2 encodes for the junctional-adhesion-molecule-2, a key tight-junction protein in blood-brain-barrier permeability. We show that JAM2 variants lead to reduction of JAM2 mRNA expression and absence of JAM2 protein in patient’s fibroblasts, consistent with a loss-of-function mechanism. We show that the human phenotype is replicated in the jam2 complete knockout mouse (jam2 KO). Furthermore, neuropathology of jam2 KO mouse showed prominent vacuolation in the cerebral cortex, thalamus, and cerebellum and particularly widespread vacuolation in the midbrain with reactive astrogliosis and neuronal density reduction. The regions of the human brain affected on neuroimaging are similar to the affected brain areas in the myorg PFBC null mouse. Along with JAM3 and OCLN, JAM2 is the third tight-junction gene in which bi-allelic variants are associated with brain calcification, suggesting that defective cell-to-cell adhesion and dysfunction of the movement of solutes through the paracellular spaces in the neurovascular unit is a key mechanism in CNS calcification.

The Genetic Landscape of Dystrophin Mutations in Italy: A Nationwide Study

Dystrophinopathies are inherited diseases caused by mutations in the dystrophin (DMD) gene for which testing is mandatory for genetic diagnosis, reproductive choices and eligibility for personalized trials. We genotyped the DMD gene in our Italian cohort of 1902 patients (BMD n = 740, 39%; DMD n =1162, 61%) within a nationwide study involving 11 diagnostic centers in a 10-year window (2008–2017). In DMD patients, we found deletions in 57%, duplications in 11% and small mutations in 32%. In BMD, we found deletions in 78%, duplications in 9% and small mutations in 13%. In BMD, there are a higher number of deletions, and small mutations are more frequent than duplications. Among small mutations that are generally frequent in both phenotypes, 44% of DMD and 36% of BMD are nonsense, thus, eligible for stop codon read-through therapy; 63% of all out-of-frame deletions are eligible for single exon skipping. Patients were also assigned to Italian regions and showed interesting regional differences in mutation distribution. The full genetic characterization in this large, nationwide cohort has allowed us to draw several correlations between DMD/BMD genotype landscapes and mutation frequency, mutation types, mutation locations along the gene, exon/intron architecture, and relevant protein domain, with effects on population genetic characteristics and new personalized therapies.

Biallelic intragenic duplication in ADGRB3 (BAI3) gene associated with intellectual disability, cerebellar atrophy, and behavioral disorder

In recent years, chromosomal microarray analysis has permitted the discovery of rearrangements underlying several neurodevelopmental disorders and still represents the first diagnostic test for unexplained neurodevelopmental disabilities. Here we report a family of consanguineous parents showing psychiatric disorders and their two sons both affected by intellectual disability, ataxia, and behavioral disorder. SNP/CGH array analysis in this family demonstrated in both siblings a biallelic duplication inherited from the heterozygous parents, disrupting the ADGRB3 gene. ADGRB3, also known as BAI3, belongs to the subfamily of adhesion G protein-coupled receptors (adhesion GPCRs) that regulate many aspects of the central nervous system, including axon guidance, myelination, and synapse formation. Single nucleotide polymorphisms and copy number variants involving ADGRB3 have recently been associated with psychiatric disorders. These findings further support this association and also suggest that biallelic variants affecting the function of the ADGRB3 gene may also cause cognitive impairments and ataxia.

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

PRUNE is a member of the DHH (Asp-His-His) phosphoesterase protein superfamily of molecules important for cell motility, and implicated in cancer progression. Here we investigated multiple families from Oman, India, Iran and Italy with individuals affected by a new autosomal recessive neurodevelopmental and degenerative disorder in which the cardinal features include primary microcephaly and profound global developmental delay. Our genetic studies identified biallelic mutations of PRUNE1 as responsible. Our functional assays of disease-associated variant alleles revealed impaired microtubule polymerization, as well as cell migration and proliferation properties, of mutant PRUNE. Additionally, our studies also highlight a potential new role for PRUNE during microtubule polymerization, which is essential for the cytoskeletal rearrangements that occur during cellular division and proliferation. Together these studies define PRUNE as a molecule fundamental for normal human cortical development and define cellular and clinical consequences associated with PRUNE mutation.

The 9-bp deletion in region V of mtDNA: a risk factor of hearing loss and encephalomyopathy in Caucasian populations?

A deletion of one of the two copies of the 9-bp tandem repeat sequence (CCCCCTCTA), in the small non-coding/untranslated segment located between the cytochrome oxidase II and lysine tRNA genes of mitochondrial DNA (mtDNA), has previously been used as a polymorphic anthropological marker (MIC9D) for people of Africa and Asia, but it has been rarely reported in Europe. 32 Sicilian patients with syndromic hearing loss, negative for mutations in GJB2 and GJB6 genes, were tested for mtDNA known point mutations associated with syndromic or non-syndromic hearing loss by RFLP and/or direct sequencing. We identified the presence of the MIC9D in homoplasmy in lymphocytes and muscle of three subjects with sensorineural hearing loss and encephalomyopathy, two of these also presented moderate mental retardation. This deletion was absent in 300 Caucasian controls. Although further studies are warranted, our results suggest that the MIC9D polymorphism could have a susceptibility role in Caucasus, such as Sicily population.

Coexistence of mitochondrial and nuclear DNA mutations in a woman with mitochondrial encephalomyopathy and double cortex

We describe a 16-year-old girl with mental retardation, myoclonic epilepsy, ataxia, mitochondrial myopathy, sensorineural hearing loss, lactic acidosis, and MRI evidence of diffuse subcortical laminar heterotopia and agyria/pachygyria. Restriction fragment length polymorphism (RFLP) and DNA sequence analyses revealed two pathogenic mutations: a heteroplasmic m.3243A>G in muscle and blood, and a new heterozygous insertion at nt697 in the doublecortin gene (DCX), resulting in a frameshift after amino acid residue 232, with a premature stop codon at amino acid residue 244. This is yet another example of genetic "double trouble" resulting in a complex phenotype.

Posterior fossa abnormalities in hereditary spastic paraparesis with spastin mutations

BACKGROUND

Hereditary spastic paraparesis (HPS) linked to mutations in the spastin gene (SPG4) is considered to be a pure form of spastic hereditary paraparesis. However, in this disease also other signs of central nervous system involvement are frequently found.

METHODS

Clinical, genetical and neuroradiological investigations were carried out in a large family with autosomal dominant spastic paraparesis and in a sporadic case with spastic paraparesis.

RESULTS

Additional clinical and molecular data are provided, studying other members of the same pedigree, as already described, with a five-base deletion in exon 9 of the SPG4 gene (1215-1219delTATAA) whose members show MRI anomalies that fall within the Dandy-Walker continuum. Furthermore, an unrelated female patient with hypoplasia of the cerebellar vermis is indicated, carrying a de novo previously reported mutation of the SPG4 gene (c.1741C>T p.R581X).

CONCLUSIONS

Spastin may play an important role in the development of the central nervous system and in particular in the development of the structures of posterior fossa.

Expression of SpanX mRNA in testicular germ cell tumors

The function of SpanX proteins is unknown, evidence is accumulating to suggest their involvement in tumorigenesis. A locus in Xq27, where the SpanX gene family is located, has been associated with testicular germ cell tumor (TGCT) onset. Therefore, we evaluated the presence of SpanX mRNA in six TGCT cases by RT-PCR. The results showed that SpanX mRNA is present in TGCT, confirming transcriptional activity of these genes in such tumors.

Severe encephalomyopathy in a patient with homoplasmic A5814G point mutation in mitochondrial tRNACys gene

We report a patient with severe encephalomyopathy and homoplasmic A5814G point mutation in the mitochondrial DNA tRNA gene for cysteine. This mutation had been reported in heteroplasmic condition in patients with different clinical phenotypes. Our results confirm the pathogenicity of the mutation and support the concept that homoplasmic mutations in tRNA genes can be responsible for mitochondrial disorders with variable penetrance. This report also extends the clinical spectrum associated with the A5814G mutation.

Mutational analysis of the ATRX gene by DGGE: a powerful diagnostic approach for the ATRX syndrome

Molecular defects affecting the ATRX gene lead to the ATRX syndrome (alpha thalassemia/mental retardation syndrome, X-linked), characterized by severe mental retardation, microcephaly, distinct facial dysmorphism, and genital abnormalities, as well as a wide spectrum of other pathological features. Alpha thalassemia is frequent but does not represent a constant characteristic of the syndrome. An expanding phenotype of the ATRX gene (a RAD54 homologue encoding a putative zinc-finger helicase) has been demonstrated as a result of the association of single mutations with specific X-linked mental retardation syndromes. To date, mutational analysis of the gene has been based on direct DNA sequencing or using methods with a lower detection rate. In this paper, we present a broad-range DGGE method for single-step mutation scanning of the entire open reading frame (ORF) and canonical splice sites of the gene. Using this method, we successfully identified five novel sequence changes in the ATRX gene, including four missense mutations (K1733E, R2085C, D2136N, T2169A) and one polymorphism (IVS5+35G>A).