Variable clinical severity in TANGO2 deficiency: Case series and literature review

Biallelic pathogenic variants in the TANGO2 (transport and Golgi organization 2 homolog) gene have been identified as causing a rare metabolic disorder characterized by susceptibility to recurrent rhabdomyolysis, lactic acidosis, encephalopathy, and life-threatening tachyarrhythmias. Recently published reports suggest variable clinical severity and phenotypes. This study details five new patients from two families with biallelic pathogenic variants in the TANGO2 gene identified by whole exome sequencing and includes the largest number of affected individuals from a single family reported to date. We document significant intrafamilial variability and highlight that milder phenotypes may be underrecognized. We present biochemical and clinical data to help highlight the features that aid in consideration of this condition in the differential with disorders of fatty acid oxidation. We also present a comprehensive literature review summarizing the molecular, clinical, and biochemical findings for 92 individuals across 13 publications. Of the 27 pathogenic variants reported to date, the recurrent exons 3-9 deletion represents the most common variant seen in 42% of individuals with TANGO2 deficiency. Common clinical features seen in >70% of all individuals include acute metabolic crisis, rhabdomyolysis, neurologic abnormalities, developmental delay, and intellectual disability. Findings such as elevated creatine kinase, hypothyroidism, ketotic hypoglycemia, QT prolongation, or abnormalities of long-chain acylcarnitines and urine dicarboxylic acids should raise clinical suspicion for this life-threatening condition.

Hypermethylation of the CpG island near the G4C2 repeat in ALS with a C9orf72 expansion

The G4C2 repeat expansion in C9orf72 is the most common known cause of amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD). We tested the hypothesis that the repeat expansion causes aberrant CpG methylation near the G4C2 repeat, which could be responsible for the downregulation of gene expression. We investigated the CpG methylation profile by two methods using genomic DNA from the blood of individuals with ALS (37 expansion carriers and 64 noncarriers), normal controls (n = 76), and family members of 7 ALS probands with the expansion. We report that hypermethylation of the CpG island 5' of the G4C2 repeat is associated with the presence of the expansion (p < 0.0001). A higher degree of methylation was significantly correlated with a shorter disease duration (p < 0.01), associated with familial ALS (p = 0.009) and segregated with the expansion in 7 investigated families. Notably, we did not detect methylation for either normal or intermediate alleles (up to 43 repeats), bringing to question the current cutoff of 30 repeats for pathological alleles. Our study raises several important questions for the future investigation of large data sets, such as whether the degree of methylation corresponds to clinical presentation (ALS versus FTLD).

Chromosome 9 ALS and FTD locus is probably derived from a single founder

We and others have recently reported an association between amyotrophic lateral sclerosis (ALS) and single nucleotide polymorphisms on chromosome 9p21 in several populations. Here we show that the associated haplotype is the same in all populations and that several families previously shown to have genetic linkage to this region also share this haplotype. The most parsimonious explanation of these data are that there is a single founder for this form of disease.

Two Italian kindreds with familial amyotrophic lateral sclerosis due to FUS mutation

Recently, fused in sarcoma/translated in liposarcoma (FUS/TLS) gene, located on chromosome 16p11.2, has been identified as a disease gene in familial amyotrophic lateral sclerosis (FALS). We have analyzed FUS/TLS in a cohort of 52 index cases from seven Italian regions with non-SOD1 and non-TARDBP FALS. We identified a heterozygous c.G1542C missense mutation in a family of northern Italian origin, and a heterozygous c.C1574T missense mutation in a family of Sicilian origin. Both variants are located in exon 15 encoding the RNA-recognition motif, and result in a substitution of an arginine with a serine in position 514 (p.R514S) and substitution of a proline with a leucine at position 525 (p.P525L), respectively. Overall, the two mutations accounted for 3.8% of 52 non-SOD1 and non-TDP43 index cases of FALS. The clinical phenotype was similar within each of the families, with a predominantly upper limb onset in the family carrying the p.R514S mutation and bulbar onset, with very young age and a rapid course in the family carrying the p.P525L mutation.

Genome-wide genotyping in Parkinson's disease and neurologically normal controls: first stage analysis and public release of data

BACKGROUND

Several genes underlying rare monogenic forms of Parkinson's disease have been identified over the past decade. Despite evidence for a role for genetics in sporadic Parkinson's disease, few common genetic variants have been unequivocally linked to this disorder. We sought to identify any common genetic variability exerting a large effect in risk for Parkinson's disease in a population cohort and to produce publicly available genome-wide genotype data that can be openly mined by interested researchers and readily augmented by genotyping of additional repository subjects.

METHODS

We did genome-wide, single-nucleotide-polymorphism (SNP) genotyping of publicly available samples from a cohort of Parkinson's disease patients (n=267) and neurologically normal controls (n=270). More than 408,000 unique SNPs were used from the Illumina Infinium I and HumanHap300 assays.

FINDINGS

We have produced around 220 million genotypes in 537 participants. This raw genotype data has been and as such is the first publicly accessible high-density SNP data outside of the International HapMap Project. We also provide here the results of genotype and allele association tests.

INTERPRETATION

We generated publicly available genotype data for Parkinson's disease patients and controls so that these data can be mined and augmented by other researchers to identify common genetic variability that results in minor and moderate risk for disease.