Dulce Quelhas

Golgi function and dysfunction in the first COG4-deficient CDG type II patient

The conserved oligomeric Golgi (COG) complex is a hetero-octameric complex essential for normal glycosylation and intra-Golgi transport. An increasing number of congenital disorder of glycosylation type II (CDG-II) mutations are found in COG subunits indicating its importance in glycosylation. We report a new CDG-II patient harbouring a p.R729W missense mutation in COG4 combined with a submicroscopical deletion. The resulting downregulation of COG4 expression additionally affects expression or stability of other lobe A subunits. Despite this, full complex formation was maintained albeit to a lower extent as shown by glycerol gradient centrifugation. Moreover, our data indicate that subunits are present in a cytosolic pool and full complex formation assists tethering preceding membrane fusion. By extending this study to four other known COG-deficient patients, we now present the first comparative analysis on defects in transport, glycosylation and Golgi ultrastructure in these patients. The observed structural and biochemical abnormalities correlate with the severity of the mutation, with the COG4 mutant being the mildest. All together our results indicate that intact COG complexes are required to maintain Golgi dynamics and its associated functions. According to the current CDG nomenclature, this newly identified deficiency is designated CDG-IIj.

Dietary treatment in phenylketonuria does not lead to increased risk of obesity or metabolic syndrome

BACKGROUND Little is known about the consequences of the special energy enriched diet used to treat patients with phenylketonuria (PKU) in terms of obesity and metabolic syndrome (MetSyn) development. OBJECTIVE To investigate the prevalence of overweight and obesity, and its consequences in terms of body composition and MetSyn in early treated patients with PKU compared to controls. DESIGN A sample of 89 patients with PKU (3-30 y; 14.4±6.6 y) and 79 controls (3-47 y; 16.3±7.9 y) were studied. In the fasted state, anthropometric, body composition, blood pressure and analytical parameters [amino acids, glucose, insulin, total and HDL-cholesterol (HDL-c), triglycerides (TG), high sensitivity c-reactive protein and uric acid] were performed. Data on dietary intake was collected. BMI was classified using WHO criteria, while the definition from International Diabetes Federation (IDF) was used for MetSyn. RESULTS Prevalence of overweight and obesity (32.6% vs. 24.1%; p=0.293), body fat percentage (22% vs. 23.1%, p=0.581) and central obesity (36.9% vs. 36.4%, p=0.999) were comparable to controls. Patients revealed a higher TG/HDL-c (p<0.001). The prevalence of MetSyn was 1.5% and 6.1% in patients and controls, respectively. Patients and not controls with central obesity revealed a further significant increase in TG/HDL-c compared with those without central obesity (p=0.023). CONCLUSION Patients and controls were similar in terms of overweight and obesity, body composition and MetSyn. However, the dyslipidemia in patients with PKU in relation to overweight and obesity may help us trying to understand the course and the etiology of MetSyn not only in PKU but also in the general population.

CCDC115 Deficiency Causes a Disorder of Golgi Homeostasis with Abnormal Protein Glycosylation

Disorders of Golgi homeostasis form an emerging group of genetic defects. The highly heterogeneous clinical spectrum is not explained by our current understanding of the underlying cell-biological processes in the Golgi. Therefore, uncovering genetic defects and annotating gene function are challenging. Exome sequencing in a family with three siblings affected by abnormal Golgi glycosylation revealed a homozygous missense mutation, c.92T>C (p.Leu31Ser), in coiled-coil domain containing 115 (CCDC115), the function of which is unknown. The same mutation was identified in three unrelated families, and in one family it was compound heterozygous in combination with a heterozygous deletion of CCDC115. An additional homozygous missense mutation, c.31G>T (p.Asp11Tyr), was found in a family with two affected siblings. All individuals displayed a storage-disease-like phenotype involving hepatosplenomegaly, which regressed with age, highly elevated bone-derived alkaline phosphatase, elevated aminotransferases, and elevated cholesterol, in combination with abnormal copper metabolism and neurological symptoms. Two individuals died of liver failure, and one individual was successfully treated by liver transplantation. Abnormal N- and mucin type O-glycosylation was found on serum proteins, and reduced metabolic labeling of sialic acids was found in fibroblasts, which was restored after complementation with wild-type CCDC115. PSI-BLAST homology detection revealed reciprocal homology with Vma22p, the yeast V-ATPase assembly factor located in the endoplasmic reticulum (ER). Human CCDC115 mainly localized to the ERGIC and to COPI vesicles, but not to the ER. These data, in combination with the phenotypic spectrum, which is distinct from that associated with defects in V-ATPase core subunits, suggest a more general role for CCDC115 in Golgi trafficking. Our study reveals CCDC115 deficiency as a disorder of Golgi homeostasis that can be readily identified via screening for abnormal glycosylation in plasma.

De Barsy syndrome and ATP6V0A2-CDG.

We read with interest the nice review of Morava et al1 on the autosomal recessive cutis laxa syndromes. The authors mention the De Barsy syndrome and state that the genetic background of the De Barsy syndrome has not yet been identified. However, in the paper by Kornak et al2 on impaired glycosylation and cutis laxa caused by mutations in ATP6V0A2 (ATP6V0A2-CDG according to the novel nomenclature3, 4), one of the patients (see patient CoFe in Table 1 of Kornak et al2) shows the full clinical picture of the De Barsy syndrome, including cutis laxa, facial dysmorphy, dwarfism, psychomotor retardation, dystonia, congenital hip dysplasia, and corneal dystrophy necessitating repeated corneal transplantation. These data suggest that a subgroup of patients with De Barsy syndrome5 belongs to the spectrum of ATP6V0A2-CDG. Another cause of De Barsy syndrome has very recently been identified as mutations in PYCR1, coding for a mitochondrial enzyme involved in proline metabolism.6 Therefore, we recommend a systematic screen for ATP6V0A2-CDG and for mutations in PYCR1 in patients with De Barsy syndrome.

Congenital disorders of glycosylation with neonatal presentation

Congenital disorders of glycosylation (CDG) are a group of hereditary diseases characterised by deficiency of enzymes involved in proteins glycosylation. We describe the clinical case of a neonate with CDG type 1a, nowadays designated phosphomannomutase 2 (PMM2)-CDG. Physical examination showed an abnormal facies, axial hypotonia, abnormal fat distribution, inverted nipples, non-palpable testicles and arachnodactyly. Progressive multiple system organ involvement and worsening of hypertrophic cardiomyopathy occurred. Metabolic study revealed a CDG disturbance, which was confirmed by genetic study. The following mutations were identified: c.193G>T; p.D65Y and c.470T>C; p.F157S. Clinical deterioration was inevitable with multisystemic failure and death. CDG represents a challenge for physicians due to multiple organ involvement, and heterogeneous clinical manifestations. The neonatal form is usually associated with the worst prognosis.

Renal involvement in PMM2-CDG, a mini-review

Phosphomannomutase 2 deficiency (PMM2-CDG) is the most common N-linked glycosylation disorder. The majority of patients present with a multisystem phenotype, including central nervous system involvement, hepatopathy, gastrointestinal and cardiac symptoms, endocrine dysfunction and abnormal coagulation. Renal abnormalities including congenital malformations and altered renal function are part of the multisystem manifestations of congenital disorders of glycosylation. We reviewed the literature on 933 patients with molecularly and/or enzymatically confirmed PMM2 deficiency to evaluate the incidence of renal involvement in PMM2-CDG. Renal abnormalities were reported in 56 patients. Congenital abnormalities were present in 41 out of these 55. Cystic kidney and mild proteinuria were the most common findings. One of the most severe renal manifestations, congenital nephrotic syndrome, was detected in 6 children. Renal manifestations were not associated with the presence of specific PMM2 alleles. This review summarizes the reported renal abnormalities in PMM2-CDG and draws attention to the pathophysiological impact of abnormal glycosylation on kidney structure and function.

Mutation analysis of the PAH gene in phenylketonuria patients from Rio de Janeiro, Southeast Brazil

Phenylketonuria (PKU) is an autosomal recessive disease resulting from mutations in the PAH gene. Most of the patients are compound heterozygotes, and genotype is a major factor in determining the phenotypic variability of PKU. More than 1,000 variants have been described in the PAH gene. Rio de Janeiros population has a predominance of Iberian, followed by African and Amerindian ancestries. It is expected that most PKU variants in this Brazilian state have originated in the Iberian Peninsula. However, rare European, African or pathogenic variants that are characteristic of the admixed population of the state might also be found.