Neurogenetics

Association of ATXN2 intermediate-length CAG repeats with amyotrophic lateral sclerosis correlates with the distributions of normal CAG repeat alleles among individual ethnic populations Abstract Intermediate-length CAG repeats in ATXN2 have been widely shown to be a risk factor for sporadic amyotrophic lateral sclerosis (SALS). To evaluate the association of ATXN2 intermediate-length CAG repeat alleles with an increased risk of SALS, we investigated distributions of CAG repeat alleles in 394 patients with SALS and 490 control individuals in the Japanese population. In the intermediate-length repeat units of 29 or more, we identified one SALS patient with 31 repeat units and two control individuals with 30 repeat units. Thus, no significant differences in the carrier frequency of intermediate-length CAG repeat alleles were detected between patients with SALS and control individuals. When we investigated the distribution of "large normal alleles" defined as ATXN2 CAG repeats ranging from 24 up to 33 in the Japanese population compared with those in other populations in previous studies, the frequency of large normal alleles was significantly higher in the European and North American series than in the Japanese series. Moreover, these frequencies in the Turkish, Chinese, Korean, and Brazilian (Latin American) series were also higher than that in the Japanese series. These results raise the possibility that the frequencies of large normal alleles in individual populations underlie the frequencies of ALS risk alleles in the corresponding populations.

Truncating biallelic variant in DNAJA1 , encoding the co-chaperone Hsp40, is associated with intellectual disability and seizures Abstract Intellectual disability poses a huge burden on the health care system, and it is one of the most common referral reasons to the genetic and child neurology clinic. Intellectual disability (ID) is genetically heterogeneous, and it is associated with several other neurological conditions. Exome sequencing is a robust genetic tool and has revolutionized the process of molecular diagnosis and novel gene discovery. Besides its diagnostic clinical value, novel gene discovery is prime in reverse genetics, when human mutations help to understand the function of a gene and may aid in better understanding of the human brain and nervous system. Using WES, we identified a biallelic truncating variant in DNAJA1 gene (c.511C>T p.(Gln171*) in a multiplex Saudi consanguineous family. The main phenotype shared between the siblings was intellectual disability and seizure disorder.

Rs10230207 genotype confers changes in HDAC9 and TWIST1 , but not FERD3L in lymphoblasts from patients with intracranial aneurysm Abstract Intracranial aneurysms (IA) are weakened outpouchings of the arterial wall in the cerebrovasculature. Rupture of an IA often leads to devastating consequences. The early identification of IA patients is crucial for management of their condition. A genetic variant at rs10230207, located nearby the HDAC9, TWIST1, and FERD3L genes, is associated with IA. HDAC9 is a class IIa histone deacetylase that mediates vascular smooth muscle cell dysfunction. TWIST1 is a mechanosensitive transcription factor and its expression is reduced in unstable carotid atherosclerotic plaques. In this study, the expression of the HDAC9, TWIST1, and FERD3L genes was characterized and associated with the presence of the rs10230207 genetic variant. Allelic discrimination and gene expression analysis were performed using lymphoblasts from 85 population controls and 109 IA patients. Subjects that were heterozygous (GT) within rs10230207 were 4.32 times more likely to have an IA than those that were homozygous for the reference allele (GG; 95%CI 1.23 to 14.16). Subjects that were homozygous (TT) were 8.27 times more likely to have an IA than those that were GG (95%CI 2.45 to 27.85). While the presence of the risk allele was not associated with changes in FERD3L gene expression, the risk allele was associated with increased HDAC9 and decrease in TWIST1 mRNA expression. The significant inverse correlation between HDAC9 and TWIST1 gene expression suggests that changes in the expression of both of genes may contribute to the formation of IAs.

Primary familial brain calcification caused by a novel homozygous MYORG mutation in a consanguineous Italian family Abstract Primary familial brain calcification (PFBC) is a rare disorder mostly characterized by calcium deposits in the basal ganglia and a wide spectrum of neurologic and psychiatric symptoms, typically inherited as an autosomal dominant trait. Recently, MYORG was reported as the first autosomal recessive causal gene in PFBC patients of Chinese and Middle Eastern origin. Herein, we describe the first PFBC patient of European descent found to carry a novel homozygous MYORG mutation (p.N511Tfs*243). Interestingly, the patient's father, a heterozygous carrier of the same mutation, showed diffuse bilateral cerebral calcifications with no symptoms other than very mild postural tremor.

Celia's encephalopathy and c.974dupG in BSCL2 gene: a hidden change in a known variant Abstract Celia's encephalopathy (progressive encephalopathy with/without lipodystrophy (PELD)) is a childhood neurodegenerative disorder with a fatal prognosis before the age of 10, due to the variant c.985C>T in the BSCL2gene that causes a cryptic splicing site leading to skipping of exon 7. For years, different authors have reported cases of congenital generalized lipodystrophy due to the variant c.974dupG in BSCL2 associated with neurological manifestations of variable severity, although some of them clearly superimposable to PELD. To identify the molecular mechanisms responsible for these neurological alterations in two patients with c.974dupG. Clinical characterization, biochemistry, and neuroimaging studies of two girls carrying this variant. In silico analysis, PCR amplification, and BSCL2 cDNA sequencing. BSCL2-201 transcript expression, which lacks exon 7, by qPCR in fibroblasts from the index case, from a healthy child as a control and from two patients with PELD, and in leukocytes from the index case and her parents. One with a severe encephalopathy including a picture of intellectual deficiency, severe language impairment, myoclonic epilepsy, and lipodystrophy as described in PELD, dying at 9 years and 9 months of age. The other 2-year-old patient showed incipient signs of neurological involvement. In silico and cDNA sequencing studies showed that variant c.974dupG gives rise to skipping of exon 7. The expression of BSCL2-201 in fibroblasts was significantly higher in the index case than in the healthy child, although less than in the case with homozygous PELD due to c.985C>T variant. The expression of this transcript was approximately half in the healthy carrier parents of this patient. The c.974dupG variant leads to the skipping of exon 7 of the BSCL2 gene and is responsible for a variant of Celia's encephalopathy, with variable phenotypic expression.

Overlap of polymicrogyria, hydrocephalus, and Joubert syndrome in a family with novel truncating mutations in ADGRG1/GPR56 and KIAA0556 Abstract Genetic mutations associated with brain malformations can lead to a spectrum of severity and it is often difficult to determine whether there are additional pathogenic variants contributing to the phenotype. Here, we present a family affected by a severe brain malformation including bilateral polymicrogyria, hydrocephalus, patchy white matter signal changes, and cerebellar and pontine hypoplasia with elongated cerebellar peduncles leading to the molar tooth sign. While the malformation is reminiscent of bilateral frontoparietal polymicrogyria (BFPP), the phenotype is more severe than previously reported and also includes features of Joubert syndrome (JBTS). Via exome sequencing, we identified homozygous truncating mutations in both ADGRG1/GPR56 and KIAA0556, which are known to cause BFPP and mild brain-specific JBTS, respectively. This study shows how two independent mutations can interact leading to complex brain malformations.

Pathogenic variants in AIMP1 cause pontocerebellar hypoplasia Abstract Aminoacyl-tRNA synthetase-interacting multifunctional protein 1 (AIMP1) is a non-catalytic component of the multi-tRNA synthetase complex which catalyzes the ligation of amino acids to the correct tRNAs. Pathogenic variants in several aminoacyl-tRNA synthetases genes have been linked to various neurological disorders, including leukodystrophies and pontocerebellar hypoplasias (PCH). To date, loss-of-function variants in AIMP1have been associated with hypomyelinating leukodystrophy-3 (MIM 260600). Here, we report a novel frameshift AIMP1 homozygous variant (c.160delA,p.Lys54Asnfs) in a child with pontocerebellar hypoplasia and simplified gyral pattern, a phenotype not been previously described with AIMP1 variants, thus expanding the phenotypic spectrum. AIMP1 should be included in diagnostic PCH gene panels.

Facioscapulohumeral muscular dystrophy (FSHD) molecular diagnosis: from traditional technology to the NGS era Abstract Facioscapulohumeral muscular dystrophy (FSHD) is a genetic neuromuscular disorder which mainly affects the muscles of the face, shoulder, and upper arms. FSHD is generally associated with the contraction of D4Z4macrosatellite repeats on 4q35 chromosome or mutations in SMCHD1, which are responsible of the toxic expression of DUX4 in muscle tissue. Despite the recent application of NGS techniques in the clinical practice, the molecular diagnosis of FSHD is still performed with dated techniques such as Southern blotting. The diagnosis of FSHD requires therefore specific skills on both modern and less modern analytical protocols. Considering that clinical and molecular diagnosis of FSHD is challenging, it is not surprising that only few laboratories offer a comprehensive characterization of FSHD, which requires the education of professionals on traditional techniques even in the era of NGS. In conclusion, the study of FSHD provides an excellent example of using classical and modern molecular technologies which are equally necessary for the analysis of DNA repetitive traits associated with specific disorders.

Linkage analysis and whole exome sequencing reveals AHNAK2 as a novel genetic cause for autosomal recessive CMT in a Malaysian family Abstract Charcot-Marie-Tooth (CMT) disease is a form of inherited peripheral neuropathy that affects motor and sensory neurons. To identify the causative gene in a consanguineous family with autosomal recessive CMT (AR-CMT), we employed a combination of linkage analysis and whole exome sequencing. After excluding known AR-CMT genes, genome-wide linkage analysis mapped the disease locus to a 7.48-Mb interval on chromosome 14q32.11–q32.33, flanked by the markers rs2124843 and rs4983409. Whole exome sequencing identified two non-synonymous variants (p.T40P and p.H915Y) in the AHNAK2 gene that segregated with the disease in the family. Pathogenic predictions indicated that p.T40P is the likely causative allele. Analysis of AHNAK2 expression in the AR-CMT patient fibroblasts showed significantly reduced mRNA and protein levels. AHNAK2 binds directly to periaxin which is encoded by the PRX gene, and PRX mutations are associated with another form of AR-CMT (CMT4F). The altered expression of mutant AHNAK2 may disrupt the AHNAK2-PRX interaction in which one of its known functions is to regulate myelination.

PTCD3 mutations cause Leigh-like rather than Leigh syndrome