A homozygous splice variant in ATP5PO, disrupts mitochondrial complex V function and causes Leigh syndrome in two unrelated families

Mitochondrial complex V plays an important role in oxidative phosphorylation by catalyzing the generation of ATP. Most complex V subunits are nuclear encoded and not yet associated with recognized Mendelian disorders. Using exome sequencing, we identified a rare homozygous splice variant (c.87+3A>G) in ATP5PO, the complex V subunit which encodes the oligomycin sensitivity conferring protein, in three individuals from two unrelated families, with clinical suspicion of a mitochondrial disorder. These individuals had a similar, severe infantile and often lethal multi-systemic disorder that included hypotonia, developmental delay, hypertrophic cardiomyopathy, progressive epileptic encephalopathy, progressive cerebral atrophy, and white matter abnormalities on brain MRI consistent with Leigh syndrome. cDNA studies showed a predominant shortened transcript with skipping of exon 2 and low levels of the normal full-length transcript. Fibroblasts from the affected individuals demonstrated decreased ATP5PO protein, defective assembly of complex V with markedly reduced amounts of peripheral stalk proteins, and complex V hydrolytic activity. Further, expression of human ATP5PO cDNA without exon 2 (hATP5PO-∆ex2) in yeast cells deleted for yATP5 (ATP5PO homolog) was unable to rescue growth on media which requires oxidative phosphorylation when compared to the wild type construct (hATP5PO-WT), indicating that exon 2 deletion leads to a non-functional protein. Collectively, our findings support the pathogenicity of the ATP5PO c.87+3A>G variant, which significantly reduces but does not eliminate complex V activity. These data along with the recent report of an affected individual with ATP5PO variants, add to the evidence that rare biallelic variants in ATP5PO result in defective complex V assembly, function and are associated with Leigh syndrome.

Heterozygous HMGB1 loss-of-function variants are associated with developmental delay and microcephaly

13q12.3 microdeletion syndrome is a rare cause of syndromic intellectual disability. Identification and genetic characterization of patients with 13q12.3 microdeletion syndrome continues to expand the phenotypic spectrum associated with it. Previous studies identified four genes within the approximately 300 Kb minimal critical region including two candidate protein coding genes: KATNAL1 and HMGB1. To date, no patients carrying a sequence-level variant or a single gene deletion in HMGB1 or KATNAL1 have been described. Here we report six patients with loss-of-function variants involving HMGB1 and who had phenotypic features similar to the previously described 13q12.3 microdeletion syndrome cases. Common features included developmental delay, language delay, microcephaly, obesity and dysmorphic features. In silico analyses suggest that HMGB1 is likely to be intolerant to loss-of-function, and previous in vitro data are in line with the role of HMGB1 in neurodevelopment. These results strongly suggest that haploinsufficiency of the HMGB1 gene may play a critical role in the pathogenesis of the 13q12.3 microdeletion syndrome.

Biomarkers (BM) France: Results of routine EGFR, HER2, KRAS, BRAF, PI3KCA mutations detection and EML4-ALK gene fusion assessment on the first 10,000 non-small cell lung cancer (NSCLC) patients (pts)

8000

Background: Personalized medicine is now a reality for advanced NSCLC pts on the basis of routine screening for EGFR mutation and ALK gene fusion assessment. The French NCI (INCa) also decided to additionally fund the routine assessment of 4 additional BM (HER2, KRAS, BRAF, PI3KCA). Methods: Starting on April 2012, these BM analyses were prospectively collected into a database head by the IFCT (www.ifct.fr) with 15-20,000 analyses awaited after one year. The physicians prescribing each of these BM analyses were then connected to this database and were asked to regularly complete epidemiological, clinical and therapeutic data for each corresponding patient. Results: 10,000 BM analyses were collected and entered into the BM France database at the time of this first analysis (January 2013). On the basis of available data, the patients were mainly male (63.8%), (ex)smokers (83.3%) and stage IV pts (64%). The tumors were mainly adenocarcinomas (76.1%). The samples for BM analysis were collected under bronchoscopy, surgery or transthoracic biopsy in 27.4, 28.1 and 24.2%, respectively. The 10,000 molecular profiles were characterized by 9.4% EGFR (including 0.8% EGFR resistant), 0.9% HER2, 26.9% KRAS, 1.6% BRAF, and 2.6% PI3KCA mutated and 4.0% EML4-ALK fusion genes. Double mutations were seen in 0.9% of the tumors. On January 2013, data on treatment were available for 18.6% of patients among whom 56.9% of patients received a treatment according to their molecular profile (labeled drugs or bio-guided trials). Updated data will be presented during the meeting. Conclusions: Biomarkers France is the largest ever conducted biomolecular study on advanced NSCLC patients and provides solid data on the value of a nationwide BM screening policy for NSCLC patients.