Riboflavin uptake and FAD synthesis in Saccharomyces cerevisiae mitochondria: Involvement of the Flx1p carrier in FAD export

We have studied the functional steps by which Saccharomyces cerevisiae mitochondria can synthesize FAD from cytosolic riboflavin (Rf). Riboflavin uptake into mitochondria took place via a mechanism that is consistent with the existence of (at least two) carrier systems. FAD was synthesized inside mitochondria by a mitochondrial FAD synthetase (EC 2.7.7.2), and it was exported into the cytosol via an export system that was inhibited by lumiflavin, and which was different from the riboflavin uptake system. To understand the role of the putative mitochondrial FAD carrier, Flx1p, in this pathway, an flx1Δ mutant strain was constructed. Coupled mitochondria isolated from flx1Δ mutant cells were compared with wild-type mitochondria with respect to the capability to take up Rf, to synthesize FAD from it, and to export FAD into the extramitochondrial phase. Mitochondria isolated from flx1Δ mutant cells specifically lost the ability to export FAD, but did not lose the ability to take up Rf, FAD, or FMN and to synthesize FAD from Rf. Hence, Flx1p is proposed to be the mitochondrial FAD export carrier. Moreover, deletion of the FLX1 gene resulted in a specific reduction of the activities of mitochondrial lipoamide dehydrogenase and succinate dehydrogenase, which are FAD-binding enzymes. For the flavoprotein subunit of succinate dehydrogenase we could demonstrate that this was not due to a changed level of mitochondrial FAD or to a change in the degree of flavinylation of the protein. Instead, the amount of the flavoprotein subunit of succinate dehydrogenase was strongly reduced, indicating an additional regulatory role for Flx1p in protein synthesis or degradation

McKusick-Kaufman or Bardet-Biedl syndrome? A new borderline case in an Italian nonconsanguineous healthy family

McKusick-Kaufman syndrome (MKS, OMIM #236700) is a rare syndrome inherited in an autosomal recessive pattern with a phenotypic triad comprising hydrometrocolpos (HMC), postaxial polydactyly (PAP), and congenital cardiac disease (CHD). The syndrome is caused by mutations in the MKKS gene mapped onto chromosome 20p12 between D20S162 and D20S894 markers. Mutations in the same gene causes Bardet-Biedl-6 syndrome (BBS-6, OMIM #209900) inherited in an autosomal recessive pattern. BBS-6 comprises retinitis pigmentosa, polydactyly, obesity, mental retardation, renal and genital anomalies. HMC, CHD, and PAP defects can also occur in BBS-6, and there is a significant clinical overlap between MKS and BBS-6 in childhood. We describe a new borderline case of MKS and BBS syndrome and suggest insights for understanding correlation between MKKS gene mutations and clinical phenotype. Here, we report the results of molecular analysis of MKKS in a female proband born in an Italian nonconsanguineous healthy family that presents HMC and PAP. The mutational screening revealed the presence of two different heterozygous missense variants (p.242A>S in exon 3, p.339 I>V in exon 4) in the MKKS gene, and a nucleotide variation in 5\u2032UTR region in exon 2 (-417 A>C)

Mutational Spectrum of the C1 Inhibitor Gene in a Cohort of Italian Patients with Hereditary Angioedema: Description of Nine Novel Mutations

Hereditary angioedema (HAE) is an autosomal dominant disease due to mutations in the C1 inhibitor gene (C1NH) that affects protein synthesis (HAE type I) or function (HAE type II). In 45 subjects affected by HAE diagnosed through clinical features and C1 inhibitor deficiency from the south of Italy (38 with type I and 7 with type II HAE), the whole C1NH coding region was screened for mutations by direct DNA sequencing. A severity score based on clinical manifestation, age at disease onset, and need for long-term prophylaxis was used to investigate possible genotype-phenotype correlations. A series of 22 different mutations was identified: nine missense (40.9%), five nonsense (22.7%), six frameshift (27.3), one small deletion (4.5%), and one splicing defect (4.5%). Nine C1NH mutations have not been previously described. No correlation was found between C1 inhibitor function level and severity score or age at first attack. Moreover, there was no correlation between different types of mutations and clinical phenotype. The number of different mutations identified highlights the heterogeneity of C1 inhibitor deficiency and supports the hypothesis that HAE clinical phenotype is not strictly related to the type of mutation but rather depends on unknown factors

McKusick-Kaufman or Bardet-Biedl syndrome? A new borderline case in an Italian nonconsanguineous healthy family

McKusick-Kaufman syndrome (MKS, OMIM #236700) is a rare syndrome inherited in an autosomal recessive pattern with a phenotypic triad comprising hydrometrocolpos (HMC), postaxial polydactyly (PAP), and congenital cardiac disease (CHD). The syndrome is caused by mutations in the MKKS gene mapped onto chromosome 20p12 between D20S162 and D20S894 markers. Mutations in the same gene causes Bardet-Biedl-6 syndrome (BBS-6, OMIM #209900) inherited in an autosomal recessive pattern. BBS-6 comprises retinitis pigmentosa, polydactyly, obesity, mental retardation, renal and genital anomalies. HMC, CHD, and PAP defects can also occur in BBS-6, and there is a significant clinical overlap between MKS and BBS-6 in childhood. We describe a new borderline case of MKS and BBS syndrome and suggest insights for understanding correlation between MKKS gene mutations and clinical phenotype. Here, we report the results of molecular analysis of MKKS in a female proband born in an Italian nonconsanguineous healthy family that presents HMC and PAP. The mutational screening revealed the presence of two different heterozygous missense variants (p.242A>S in exon 3, p.339 I>V in exon 4) in the MKKS gene, and a nucleotide variation in 5’UTR region in exon 2 (-417 A>C)

A novel congenital dysprothrombinemia leading to defective prothrombin maturation

Prothrombin deficiency is a very rare disorder caused by mutations in the F2 gene that generate hypoprothrombinemia or dysprothrombinemia and is characterized by bleeding manifestations that can vary from clinically irrelevant to life-threatening

Phenylalanine hydroxylase deficiency in south Italy: Genotype-phenotype correlations, identification of a novel mutant PAH allele and prediction of BH4 responsiveness

We investigated the mutation spectrum of the phenylalanine hydroxylase gene (PAH) in a cohort of patients from 33 Italian PKU families. Mutational screening of the known coding region, including conventional intron splice sites, was performed by direct sequencing of the patients' genomic DNA. Thirty-three different disease causing mutations were identified in our patient group, including 19 missense, 6 splicing, 3 nonsense, 5 deletions, with a detection rate of 100%. The most prevalent mutation was the IVS10-11G>A, accounting for 12.1% of PKU alleles studied. Other frequent mutations were: p.R261Q (9.1%), p.P281L (7.6%), and p.R408W (6.1%). We also identified one novel missense mutation, p.H290Q. A spectrum of 31 different genotypes was observed and a genotype based predictions of BH4-responsiveness were assessed. Among all genotypes, 13 were predicted to be BH4-responsive represented by thirteen PKU families. In addition, genotype-phenotype correlations were performed. This study reveals the importance of a full genotyping of PKU patients and the prediction of BH4-responsiveness, not only because of the definitive diagnosis and prediction of the optimal diet, but also to point out those patients that could benefit from new therapeutic approach. They may potentially benefit from BH4 therapy which, combined with a less strict diet, or eventually in special cases as monotherapy, may contribute to reduce nutritional deficiencies and minimize neurological and psychological dysfunctions

Mutation of angiopoietin-1 gene (ANGPT1) associates with a new type of hereditary angioedema

Hereditary angioedema (HAE) is a rare genetic disease usually due to mutation within the C1 inhibitor or the coagulation Factor XII gene. However, in a series of patients with HAE no causative variants have been described and the pathophysiology of the disease remains unknown (U-HAE). Identification of causative genes in U-HAE is valuable for understanding the cause of the disease. Objective: We conducted genetic studies in Italian patients with U-HAE to identify novel causative genes. Methods: Among patients belonging to 10 independent families and unrelated index patients with U-HAE disease recruited from the Italian network for C1-INH-HAE (ITACA), we selected a large multiplex family with U-HAE and performed whole-exome sequencing. The angiopoietin-1 gene(ANGPT1) was investigated in all patients with familial or sporadic U-HAE. The effect of ANGPT1 variants was investigated by in silico prediction and using patients and control plasmas and transfected cells. Results: We identified a missense mutation (ANGPT1, c.807G>T, p.A119S) in a family with U45 HAE. The ANGPT1 p.A119S variant was detected in all members of the index family with U-HAE but not in asymptomatic family members, nor in an additional 20 patients with familial U-HAE, 22 patients with sporadic U-HAE, and 200 controls. Protein analysis of the plasma of patients revealed a reduction of multimeric forms and a reduced ability to bind the natural receptor “tunica interna endothelial cell kinase-2” (TIE2) of the ANGPT1 p.A119S variant. The recombinant mutated ANGPT1 p.A119S formed a reduced amount of multimers and showed a reduced binding capability to its receptor. Conclusion: ANGPT1 impairment is associated with angioedema and ANGPT1 variants can be the basis of HAE

Impaired control of the contact system in hereditary angioedema with normal C1-inhibitor

Background Hereditary angioedema (HAE) comprises HAE with C1‐inhibitor deficiency (C1‐INH‐HAE) and HAE with normal C1‐INH activity (nl‐C1‐INH‐HAE), due to mutations in factor XII (FXII‐HAE), plasminogen (PLG‐HAE), angiopoietin 1 (ANGPT1‐HAE), kininogen 1 genes (KNG1‐HAE), or angioedema of unknown origin (U‐HAE). The Italian network for C1‐INH‐HAE (ITACA) created a registry including different forms of angioedema without wheals. Objective We analyzed clinical and laboratory features of a cohort of Italian subjects with nl‐C1‐INH‐HAE followed by ITACA to identify specific biomarkers. Methods A total of 105 nl‐C1‐INH‐HAE patients were studied. Plasma concentrations of cleaved high‐molecular‐weight kininogen (cHK), vascular endothelial growth factors (VEGFs), angiopoietins (Angs), and secreted phospholipase A2 enzymes (sPLA2) were evaluated. Results We identified 43 FXII‐HAE patients, 58 U‐HAE, and 4 ANGPT1‐HAE. We assessed a prevalence of 1:1.4 × 106 for FXII‐HAE and 1:1.0 × 106 for U‐HAE. cHK levels in U‐HAE patients were similar to controls in plasma collected using protease inhibitors cocktail (PIC), but they significantly increased in the absence of PIC. In FXII‐HAE patients, cHK levels, in the absence of PIC, were significantly higher than in controls. We found a significant increase of VEGF‐A, VEGF‐C, and Ang1 levels in U‐HAE patients compared to controls. In FXII‐HAE, only VEGF‐C levels were increased. Ang2 concentrations and sPLA2 activity were not modified. The levels of these mediators in ANGPT1‐HAE patients were not altered. Conclusions Our results suggest that pathogenesis of FXII‐, ANGPT1‐, and U‐HAE moves through an unbalanced control of kallikrein activity, with bradykinin as most likely mediator. VEGFs and Ang1 participate in the pathophysiology of U‐HAE increasing the basal vascular permeability