Claudio Graziano

Mutations and polymorphisms of the skeletal muscle alpha-actin gene (ACTA1).

The ACTA1 gene encodes skeletal muscle α‐actin, which is the predominant actin isoform in the sarcomeric thin filaments of adult skeletal muscle, and essential, along with myosin, for muscle contraction. ACTA1 disease‐causing mutations were first described in 1999, when a total of 15 mutations were known. In this article we describe 177 different disease‐causing ACTA1 mutations, including 85 that have not been described before. ACTA1 mutations result in five overlapping congenital myopathies: nemaline myopathy; intranuclear rod myopathy; actin filament aggregate myopathy; congenital fiber type disproportion; and myopathy with core‐like areas. Mixtures of these histopathological phenotypes may be seen in a single biopsy from one patient. Irrespective of the histopathology, the disease is frequently clinically severe, with many patients dying within the first year of life. Most mutations are dominant and most patients have de novo mutations not present in the peripheral blood DNA of either parent. Only 10% of mutations are recessive and they are genetic or functional null mutations. To aid molecular diagnosis and establishing genotype–phenotype correlations, we have developed a locus‐specific database for ACTA1 variations (http://waimr.uwa.edu.au). Hum Mutat 30:1–11, 2009.

Clinical and genetic heterogeneity in autosomal recessive nemaline myopathy

Autosomal recessive nemaline (rod) myopathy is clinically and genetically heterogeneous. A clinically distinct, typical form, with onset in infancy and a non-progressive or slowly progressive course, has been assigned to a region on chromosome 2q22 harbouring the nebulin gene Mutations have now been found in this gene, confirming its causative role. The gene for slow tropomyosin TPM3 on chromosome 1q21, previously found to cause a dominantly inherited form, has recently been found to be homozygously mutated in one severe consanguineous case. Here we wished to determine the degree of genetic homogeneity or heterogeneity of autosomal recessive nemaline myopathy by linkage analysis of 45 families from 10 countries. Forty-one of the families showed linkage results compatible with linkage to markers in the nebulin region, the highest combined lod scores at zero recombination being 14.13 for the marker D2S2236. We found no indication of genetic heterogeneity for the typical form of nemaline myopathy. In four families with more severe forms of nemaline myopathy, however, linkage to both the nebulin and the TPM3 locus was excluded. Our results indicate that at least three genetic loci exist for autosomal recessive nemaline myopathy. Studies of additional families are needed to localise the as yet unknown causative genes, and to fully elucidate genotype-phenotype correlations.

FA2H-related disorders: a novel c.270+3A>T splice-site mutation leads to a complex neurodegenerative phenotype

Homozygous mutations in the gene for fatty acid 2‐hydroxylase (FA2H) have been associated in humans with three neurodegenerative disorders: complicated spastic paraplegia (SPG35), leukodystrophy with spastic paraparesis and dystonia, and neurodegeneration with brain iron accumulation. Here, we describe a novel homozygous c.270+3A>T mutation in an Italian consanguineous family. In two affected brothers (age at molecular diagnosis 22y and 15y; age at last follow‐up 24y and 17y), altered FA2H function led to a severe phenotype, with clinical features overlapping those of the three FA2H‐associated disorders. Both patients showed childhood onset progressive spastic paraparesis, mild pyramidal and cerebellar upper limb signs, severe cognitive impairment, white‐matter disease, and cerebellar, brainstem, and spinal cord atrophy. However, absence of dystonia, drowsiness episodes, and a subtle globus pallidus involvement suggested that FA2H mutations result in a clinical spectrum, rather than causing distinct disorders. Although clinical heterogeneity is apparent, larger numbers of patients are needed to establish more accurate genotype–phenotype correlations.

Recurrent De Novo and Biallelic Variation of ATAD3A, Encoding a Mitochondrial Membrane Protein, Results in Distinct Neurological Syndromes

ATPase family AAA-domain containing protein 3A (ATAD3A) is a nuclear-encoded mitochondrial membrane protein implicated in mitochondrial dynamics, nucleoid organization, protein translation, cell growth, and cholesterol metabolism. We identified a recurrent de novo ATAD3A c.1582C>T (p.Arg528Trp) variant by whole-exome sequencing (WES) in five unrelated individuals with a core phenotype of global developmental delay, hypotonia, optic atrophy, axonal neuropathy, and hypertrophic cardiomyopathy. We also describe two families with biallelic variants in ATAD3A, including a homozygous variant in two siblings, and biallelic ATAD3A deletions mediated by nonallelic homologous recombination (NAHR) between ATAD3A and gene family members ATAD3B and ATAD3C. Tissue-specific overexpression of borR534W, the Drosophila mutation homologous to the human c.1582C>T (p.Arg528Trp) variant, resulted in a dramatic decrease in mitochondrial content, aberrant mitochondrial morphology, and increased autophagy. Homozygous null bor larvae showed a significant decrease of mitochondria, while overexpression of borWT resulted in larger, elongated mitochondria. Finally, fibroblasts of an affected individual exhibited increased mitophagy. We conclude that the p.Arg528Trp variant functions through a dominant-negative mechanism that results in small mitochondria that trigger mitophagy, resulting in a reduction in mitochondrial content. ATAD3A variation represents an additional link between mitochondrial dynamics and recognizable neurological syndromes, as seen with MFN2, OPA1, DNM1L, and STAT2 mutations.

MYO7A mutation screening in Usher syndrome type I patients from diverse origins

Usher syndrome (USH) (OMIM 276901) is an autosomal recessive disorder characterised by hearing impairment associated with retinitis pigmentosa and in some cases vestibular dysfunction. This disease accounts for approximately 50% of individuals with combined deafness and blindness in developed countries. The estimated prevalence of USH ranges from 3.8 to 6.2/100 000.1–3 Phenotypically, three clinical types of Usher syndrome have been defined according to the severity of hearing impairment, age of retinitis pigmentosa onset and the presence or absence of vestibular response. Usher syndrome type I (USH1) is the most serious type, characterised by severe to profound congenital sensorineural hearing loss, balance deficiency and prepubertal onset of retinitis pigmentosa leading to blindness. USH2 is characterised by moderate to severe hearing impairment, normal vestibular function and later onset of retinal degeneration than USH1. USH3 displays progressive hearing loss, retinitis pigmentosa and variable vestibular phenotype. Six loci for USH1 (USH1B–USH1G) have been mapped and, to date, five genes have been identified.4,5 The MYO7A gene was found to be responsible for USH1B6 and is the most common subtype of USH1, accounting for approximately 50% of cases.7–9 Defects in MYO7A also cause autosomal dominant non-syndromic sensorineural hearing impairment (DFNA11) (MIM 601317),10 autosomal recessive deafness (DFNB2) (MIM 600060)11,12 as well as atypical types of Usher syndrome which are clinically similar to USH3.13 The MYO7A gene has 49 exons, of which 48 are coding, and spans approximately 87 kb of genomic sequence on chromosome 11q13.5. The encoded protein is an unconventional myosin, the myosin VIIA,14 predicted to consist of 2215 amino acids and has a molecular mass of 254 kDa. This protein contains three typical domains: the N terminal head or motor; the neck or regulatory domain consisting of five IQ motifs; and the tail …

PRV-1, erythroid colonies and platelet Mpl are unrelated to thrombosis in essential thrombocythaemia

Females with the monoclonal type of essential thrombocythaemia (ET), based on the X‐chromosome inactivation pattern (XCIP), have previously been shown to present a higher incidence of thrombosis than polyclonal ones. We aimed to assess correlations between XCIP, thrombosis, and three epigenetic markers of ET, namely PRV‐1 overexpression, endogenous erythroid colony (EEC) formation, and reduced platelet Mpl content. Fifty‐three (60%) of 88 subjects studied had monoclonal myelopoiesis and presented a 32% incidence of major thrombosis compared with 6% of polyclonal subjects (P = 0·009). The frequency of abnormalities of PRV‐1, EEC, or Mpl was similar in monoclonal and polyclonal subjects (respectively, 28%, 48%, 75%, and 37%, 27%, 63%), and none of them correlated with thrombosis. We conclude that the exploited epigenetic markers constitute independent phenotypic variations and are not clustered according to monoclonality of myelopoiesis in ET; none of them could serve as a surrogate marker of thrombotic risk in male subjects with ET.

A de novo nonsense mutation of PAX6 gene in a patient with aniridia, ataxia, and mental retardation

Claudio Graziano, Angela V. D’Elia, Laura Mazzanti, Filomena Moscano, Simonetta Guidelli Guidi, Emanuela Scarano, Daniela Turchetti, Emilio Franzoni, Giovanni Romeo, Giuseppe Damante, and Marco Seri* U.O. di Genetica Medica, Dipartimento di Medicina Interna, Cardioangiologia ed Epatologia, Università degli Studi di Bologna, Bologna, Italy Dipartimento di Scienze e Tecnologie Biomediche, Università degli Studi di Udine, Udine, Italy Clinica Pediatrica, Dipartimento di Pediatria, Università degli Studi di Bologna, Bologna, Italy U.O. di Neuropsichiatria Infantile, Dipartimento di Pediatria, Università degli Studi di Bologna, Bologna, Italy Ottica Fisiopatologica, Policlinico S. Orsola-Malpighi, Bologna, Italy

Single gene microdeletions and microduplication of 3p26.3 in three unrelated families: CNTN6 as a new candidate gene for intellectual disability

BackgroundDetection of submicroscopic chromosomal alterations in patients with a idiopathic intellectual disability (ID) allows significant improvement in delineation of the regions of the genome that are associated with brain development and function. However, these chromosomal regions usually contain several protein-coding genes and regulatory elements, complicating the understanding of genotype-phenotype correlations. We report two siblings with ID and an unrelated patient with atypical autism who had 3p26.3 microdeletions and one intellectually disabled patient with a 3p26.3 microduplication encompassing only the CNTN6 gene.ResultsTwo 295.1-kb microdeletions and one 766.1-kb microduplication of 3p26.3 involving a single gene, CNTN6, were identified with an Agilent 60K array. Another 271.9-kb microdeletion of 3p26.3 was detected using an Affymetrix CytoScan HD chromosome microarray platform. The CHL1 and CNTN4 genes, although adjacent to the CNTN6 gene, were not affected in either of these patients.ConclusionsThe protein encoded by CNTN6 is a member of the immunoglobulin superfamily and functions as a cell adhesion molecule that is involved in the formation of axon connections in the developing nervous system. Our results indicate that CNTN6 may be a candidate gene for ID.

Genetics of human enteric neuropathies

Knowledge of molecular mechanisms that underlie development of the enteric nervous system has greatly expanded in recent decades. Enteric neuropathies related to aberrant genetic development are thus becoming increasingly recognized. There has been no recent review of these often highly morbid disorders. This review highlights advances in knowledge of the molecular pathogenesis of these disorders from a clinical perspective. It includes diseases characterized by an infantile aganglionic Hirschsprung phenotype and those in which structural abnormalities are less pronounced. The implications for diagnosis, screening and possible reparative approaches are presented.

Array CGH analysis of a cohort of Russian patients with intellectual disability.

The use of array comparative genomic hybridization (array CGH) as a diagnostic tool in molecular genetics has facilitated the identification of many new microdeletion/microduplication syndromes (MMSs). Furthermore, this method has allowed for the identification of copy number variations (CNVs) whose pathogenic role has yet to be uncovered. Here, we report on our application of array CGH for the identification of pathogenic CNVs in 79 Russian children with intellectual disability (ID). Twenty-six pathogenic or likely pathogenic changes in copy number were detected in 22 patients (28%): 8 CNVs corresponded to known MMSs, and 17 were not associated with previously described syndromes. In this report, we describe our findings and comment on genes potentially associated with ID that are located within the CNV regions.