Analysis of ASS1 gene in ten unrelated middle eastern families with citrullinemia type 1 identifies rare and novel variants

BACKGROUND

Citrullinemia type 1 (CTLN1) is a rare autosomal recessive disease caused by argininosuccinate synthetase (ASS) deficiency. Manifestations vary from the acute neonatal or "classic" form to a milder, late-onset, or "unconventional" form. To date, more than 93 variants in the ASS1 gene located on chromosome 9q43.11 (OMIM #215700) are reportedly responsible for CTLN1. Their incidence and distribution vary according to geographic origins and ethnicity, and a correlation, although not clearly delineated, has been established between the genotype and the phenotype of the disease. Though, in the Middle East, national descriptions of CTLN1 are still lacking.

METHODS

A total of ten unrelated Middle Eastern families, five Lebanese, two Syrians, and three Iraqis with citrullinemia index cases, were included in this study. Upon informed consent, DNA was extracted from the whole blood of the index patients as well as their parents and siblings. Genetic analysis was carried out by Sanger sequencing of the ASS1 gene.

RESULTS

Seven different variants were identified. Two novel variants, c.286C>A (p.(Pro96Thr), RNA not analyzed) in exon 5 and deletion c.685_688+6del(p.(Lys229Glyfs*4), RNA not analyzed) in exon 10, were found in one Lebanese and one Syrian family, respectively, and were correlated with early-onset and severe clinical presentation. Five other known variants: c.535T>C (p.(Trp179Arg), RNA not analyzed) in exon 8, c.787G>A (p.(Val263Met), RNA not analyzed) in exon 12, c.847G>A (p.(Glu283Lys), RNA not analyzed) in exon 13, c.910C>T (p.(Arg304Trp), RNA not analyzed) in exon 13, and c.1168G>A (p.(Gly390Arg), RNA not analyzed) in exon 15, were found in Lebanese, Syrian, and Iraqi families, and were associated with diverse clinical presentations.

CONCLUSION

Two novel variants and five known variants were found in a total of ten unrelated Middle Eastern families.

The added value of WES reanalysis in the field of genetic diagnosis: lessons learned from 200 exomes in the Lebanese population

Background

The past few decades have witnessed a tremendous development in the field of genetics. The implementation of next generation sequencing (NGS) technologies revolutionized the field of molecular biology and made the genetic information accessible at a large scale. However, connecting a rare genetic variation to a complex phenotype remains challenging. Indeed, identifying the cause of a genetic disease requires a multidisciplinary approach, starting with the establishment of a clear phenotype with a detailed family history and ending, in some cases, with functional assays that are crucial for the validation of the pathogenicity of a mutation.

Methods

Two hundred Lebanese patients, presenting a wide spectrum of genetic disorders (neurodevelopmental, neuromuscular or metabolic disorders, etc.), sporadic or inherited, dominant or recessive, were referred, over the last three and a half years, to the Medical Genetics Unit (UGM) of Saint Joseph University (USJ). In order to identify the genetic basis of these diseases, Whole Exome Sequencing (WES), followed by a targeted analysis, was performed for each case. In order to improve the genetic diagnostic yield, WES data, generated during the first 2 years of this study, were reanalyzed for all patients who were left undiagnosed at the genetic level. Reanalysis was based on updated bioinformatics tools and novel gene discoveries.

Results

Our initial analysis allowed us to identify the specific genetic mutation causing the disease in 49.5% of the cases, in line with other international studies. Repeated WES analysis enabled us to increase the diagnostics yield to 56%.

Conclusion

The present article reports the detailed results of both analysis and pinpoints the contribution of WES data reanalysis to an efficient genetic diagnosis. Lessons learned from WES reanalysis and interpretation are also shared.

Catheter thrombosis and superior/inferior vena cava syndrome are rare complications of long term parenteral nutrition

The objective of this study was to determine the incidence of catheter thrombosis and superior/inferior vena cava (SVC IVC ) syndrome in a large population of patients receiving home total parenteral nutrition (TPN), using retrospective data collection and analysis. 527 patients including 138 children who were discharged on home TPN and followed in the UCLA home TPN program for a minimum of one week between April, 1973 and October, 1991. There was a total of 1154 years of patients follow-up, including 241 years in children. Fifty-seven patients (11%) developed 81 episodes of catheter thrombosis excluding SVC IVC syndrome with an incidence of 0.07 episodes per catheter year. The median catheter duration prior to thrombosis was 7 months. Twenty-one thromboses occured in children with an incidence of 0.09 per catheter year. Eleven percent of thrombotic episodes were associated with catheter sepsis. Thirty-nine percent of patients had a PTT less than control values. Twenty-two patients including 6 children developed SVC IVC syndrome with an incidence of 0.02 per catheter year. SVC IVC syndrome was not associated with catheter sepsis in any patient. Sixty-eight percent of patients had catheter thrombosis at some point prior to developing SVC IVC syndrome. It is concluded that catheter-related thrombotic events are rare complications of home TPN and are uncommonly associated with infection. However, we recommend warfarin anticoagulation following an initial thrombotic event, in the absence of catheter malposition, for all such patients as long as they maintain a central venous catheter.

Chromium in parenteral nutrition: too little or too much?

Although guidelines for routine parenteral supplements of chromium (Cr) were published, there remain major concerns about the infusion of excess Cr. In addition, little information is available on appropriate dosage for intravenous usage. Cr functions as a regulator of insulin action. In humans, the 3 reported cases of Cr deficiency developed peripheral neuropathy, weight loss, and hyperglycemia. Supplementation of Cr to the parenteral nutrition (PN) solution corrected these abnormalities. For parenteral Cr, concerns arise from the high levels found in sera (up to 40-fold higher) and tissues (10- to 100-fold higher) and their effects on kidneys: In 15 children receiving long-term PN, the glomerular filtration rate was lower than that of non-PN controls and was inversely correlated with Cr indices. Furthermore, in a randomized blinded prospective protocol involving 75 newborns, the group receiving the recommended dose of Cr showed higher levels of creatinine that were positively correlated with Cr intake. Of note, Cr contaminants in PN solutions can increase the amount delivered by 10%-100%. A possible method for estimating adequate Cr to be provided IV is to calculate the amount physiologically absorbed in healthy people. This amount is 10 to 100 times less than the daily recommended parenteral Cr in adults. The accumulated scientific data presented here point to a serious need to lower the recommended amount of parenteral Cr.

Plasma choline in normal newborns, infants, toddlers, and in very-low-birth-weight neonates requiring total parenteral nutrition

Choline deficiency is associated with hepatic abnormalities in adult volunteers and patients administered total parenteral nutrition (TPN). Preliminary investigation has suggested that plasma-free choline concentration (PFCh) is greater in neonatal animals, including humans, than in adults. The aims of this study were to determine the normal PFCh and phospholipid-bound choline concentration (PPLBCh) for newborns, infants, and toddlers and to determine the change during TPN. We also sought to determine the degree of fetal choline extraction, the relation between maternal and newborn plasma choline concentrations, and the relation between plasma choline status and normal newborn length, weight, and gestational age. Blood samples were obtained from 104 full-term newborns in two centers (Ben Taub and Maimonides), 25 mothers, 21 normal infants aged 20.3 +/- 11.8 wk, 12 normal infants aged 62.4 +/- 3.9 wk, and 14 preterm infants (gestational age = 28.9 +/- 2.2 wk) who required TPN. The vein PFChs were 28.1 +/- 13.0 nmol/mL (Ben Taub) and 68.1 +/- 16.9 nmol/mL (Maimonides). The artery PFChs were 27.1 +/- 13.0 nmol/mL (Ben Taub) and 57.9 +/- 11.6 nmol/mL (Maimonides). The vein PPLChs were 1004.7 +/- 246.6 nmol/mL (Ben Taub) and 1121.2 +/- 289.6 nmol/mL (Maimonides). The artery PPLChs were 1065.7 +/- 469.3 nmol/mL (Ben Taub) and 1106.9 +/- 285.8 nmol/mL (Maimonides). The vein-minus-artery differences for PFCh were 1.0 +/- 9.7 nmol/mL (Ben Taub) and 10.2 +/- 10.9 nmol/mL (Maimonides). The vein-minus-artery differences for PPLCh were -51.9 +/- 398.2 nmol/mL (Ben Taub General Hospital, Houston, Texas) and 14.4 +/- 254.3 nmol/mL (Maimonides, New York, New York). Maternal venous PFCh was 8.4 +/- 3.1 nmol/mL. Maternal venous PPLCh was 2592.1 +/- 584.0 nmol/mL (range = 1227.8-3729.0). Maternal venous PFCh correlated with newborn arterial PFCh (r = 0.53, P < 0.05) but not with newborn venous PFCh. No correlation was seen between maternal venous and newborn PPLCh. No significant differences were seen in PPLCh or choline extraction in Ben Taub versus Maimonides patients, although PFCh was significantly greater in the newborns from Maimonides (P < 0.05). The mean venous PFCh and PPLCh in the preterm infants before beginning TPN was 21.2 +/- 6.3 and 1366.8 +/- 339.1 nmol/mL, respectively. Just before initiation of tube feeding (4.0 +/- 2.7 d after TPN had been started), mean venous PFCh and PPLCh was 18.4 +/- 5.3 and 2251.8 +/- 686.9 nmol/mL, respectively. When TPN was discontinued and tube feeding increased to goal, after 10.8 +/- 10.4 d, venous PFCh and PPLCh was 22.6 +/- 8.7 and 2072.5 +/- 540.6 nmol/mL, respectively. Venous PFCh and PPLCh was 13.4 +/- 2.5 and 1827.5 +/- 327.0 nmol/mL, respectively in the older infant group. In conclusion, newborn PFCh is significantly greater than PFCh in adults but falls to adult levels within the first year of life. Low maternal PFCh may be associated with low newborn PFCh. Normal newborn plasma choline status has no bearing on intrauterine growth, although the role of maternal choline deficiency in underweight newborns is unknown. Newborn PPLCh is substantially below that of adults, which suggests its use in membrane synthesis during growth.

Intestinal immune function is unaffected by parenteral nutrition in man

BACKGROUND

Animal studies have demonstrated intestinal immunoglobulin production is decreased when luminal nutrition is withheld and nutrition is provided solely on the basis of total parenteral nutrition (TPN).

METHODS

Eight normal volunteers were hospitalized in the Clinical Research Center for three weeks. The subjects received TPN as an exclusive means of nutritional support for 14 days followed by 5 days of enteral feeding with either standard or a glutamine- and arginine-supplemented formula in which the protein source was primarily free amino acids and peptides. Endoscopic jejunal biopsies obtained before and after TPN and following enteral refeeding were evaluated by immunofluorescence for the number of IgA, IgM and IgG-producing cells; T and B cells as well as intraepithelial and lamina propria lymphocytes were also counted. Serum immunoglobulins and the molecular forms of serum IgA were determined at the same intervals.

RESULTS

The number of intestinal IgA-, IgM- and IgG-producing cells was unaffected by TPN (676 +/- 58 vs. 643 +/- 38, 101 +/- 14 vs. 98 +/- 18, 10 +/- 1 vs. 11 +/- 2 per low power field). The total number of intestinal lymphocytes, and CD3+ lymphocytes in the intraepithelial area was unaffected by TPN (10.4 +/- 0.4 vs. 10.2 +/- 1.3, 7.3 +/- 0.8 vs. 8.6 +/- 1.6 per 100 epithelial cells). Similarly, the total number of lymphocytes and CD3+ lymphocytes in the intestinal lamina propria was unaffected by TPN (4.4 +/- 0.2 vs. 6.2 +/- 0.8, 3.3 +/- 0.7 vs. 4.5 +/- 0.8). A small, but statistically significant increase in serum IgA and IgM was seen with TPN 314 +/- 11 vs. 342 +/- 16 mg/dL and 154 +/- 25 vs. 226 +/- 47 mg/dL, although IgG remained unchanged (1262 +/- 69 vs. 1207 +/- 57 mg/dL). The proportion of polymeric and monomeric serum IgA remained unchanged after TPN (19.2 vs. 22.1% polymeric).

CONCLUSIONS

The use of TPN is not associated with intestinal immune dysfunction in man. A small, but statistically significant increase in serum IgM, and a borderline statistically significant increase in serum IgM were associated with TPN. The etiology and clinical significance of these observations is unclear.

Catheter-related infections associated with home parenteral nutrition and predictive factors for the need for catheter removal in their treatment

The inpatient and outpatient records were reviewed for 527 patients, including 138 children, who were discharged on home total parenteral nutrition and followed by the University of California, Los Angeles, home total parenteral nutrition service for a minimum of 1 week between April 1973 and October 1991. The total follow-up time was 1154 patient years; the median follow-up time was 206 days (range 7 to 6344 days). Thirty-six patients were followed for more than 10 years (median 12.7 years). Three hundred fifteen adults (but only four children) were never infected. A total of 427 catheter-related infections occurred, giving an overall infection rate of 0.37 per patient year (0.51 per patient year in children and 0.28 per patient year in patients followed for more than 10 years). Seventy percent of the infections overall were sepsis (0.26 per patient year); of those, 17% were exit site (0.06 per patient year), and 2% were tunnel (0.01 per patient year) infections. In children, 67% of the infections were sepsis (0.37 per patient year) and 24% were exit site (0.13 per patient year). Fifty-four different organisms were responsible, and 12% of the infections were polymicrobial in origin. Sixty percent of sepsis in all patients was caused by Gram-negative organisms (44% of the catheters were removed). Forty-three percent of sepsis in children was caused by Gram-negative organisms. Twenty-six percent of sepsis in all patients was caused by Gram-positive organisms (40% of the catheters were removed). Thirty-six percent of sepsis in children was caused by Gram-positive organisms.(ABSTRACT TRUNCATED AT 250 WORDS)

Selenium renal homeostasis is impaired in patients receiving long-term total parenteral nutrition

Selenium deficiency has been reported previously in patients receiving long-term total parenteral nutrition (TPN) without selenium supplementation in their solutions. The recommended dietary allowance for selenium is 0.87 microgram/kg, of which 80% is absorbed. We studied 28 adult long-term TPN patients aged 21 to 79 years (mean, 51.2 +/- 3.0 years) who have received TPN for 8.3 +/- 4.4 years. They receive 40 to 60 micrograms of selenium daily in their TPN solution. Twenty-one (75%) of 28 patients had low serum selenium levels. Of the patients with low serum selenium levels, 15 (73%) had elevated urinary selenium losses. However, no significant correlation between serum or urine selenium levels and glomerular filtration rate (measured by indium-111-diethylenetriamine pentaacetic acid clearance) or renal tubular function was observed. We conclude that the previously described renal homeostatic mechanism for selenium conservation may be significantly impaired in patients receiving long-term TPN. Such patients may require much larger doses of selenium than previously recommended. Therefore, patients receiving long-term TPN should have their serum selenium level monitored even though they receive daily selenium supplementation.

Serious renal impairment is associated with long-term parenteral nutrition

Thirty-three current long-term total parenteral nutrition (TPN) patients (13 men, 20 women) aged 21 to 79 years were prospectively studied to evaluate their change in glomerular filtration rate since beginning TPN. Creatinine clearance (CrCl) from the subject's initial home TPN clinic visit and at present were estimated from standard formulas and compared. The CrCl in 12 patients who had received home TPN for > 10 years was estimated retrospectively on a yearly basis. The estimated CrCl as an accurate measure of glomerular filtration rate was confirmed by measuring plasma indium-111 diethylenetriamine pentaacetic acid clearance. The mean daily intravenous protein intake and days during which nephrotoxic medications were used and number of bacteremic/fungemic episodes were determined for each subject. CrCl declined by 3.5 +/- 6.3% per year (p = .004). Twenty-nine of 33 patients had decreases of 0.6% to 15.4% per year. Tubular function, as determined by the tubular reabsorption of phosphate, was impaired in 52% of the subjects. The intravenous protein load averaged 1.28 +/- 0.32 g/kg per day, nephrotoxic drug use averaged 3.4 +/- 4.0% of all days on home TPN, and each patient averaged 2.3 episodes of bacteremia or fungemia since home TPN was started (0.5 +/- 0.5 episodes per year). When all factors were assessed simultaneously, nephrotoxic drug use, episodes of bacteremia/fungemia, and age accounted for approximately 46% of the variability in CrCl. When bacteremia/fungemia was expressed as a yearly rate, nephrotoxic drug use assumed no role in the glomerular filtration rate determination; infection rate and age alone accounted for 53% of the CrCl variability. We describe a profound decrease in renal function associated with long-term TPN, most of which is largely unexplained.

Total serum amylase but not lipase correlates with measured glomerular filtration rate

Elevated serum amylase and lipase levels have been reported in patients with renal failure. Because the diagnosis of pancreatitis is often based on elevations in serum amylase or lipase along with abdominal pain, we determined the relationship between total serum amylase, lipase, and glomerular filtration rate (GFR). Thirty-three subjects, 13 men and 20 women (age range, 21-79), were included in the study. There was a statistically significant correlation between serum amylase and the actual GFR (r = -0.43, p = 0.01). However, no such correlation was seen with lipase. No correlation between total serum amylase and lipase was observed. Three subjects had elevated amylase (240-433 U/L, normal 50-225). Three patients had slightly elevated lipase (29-31 U/dl, normal 8-28). All patients were asymptomatic. Of 11 subjects with GFR < 50 cc/min, only one had an elevated amylase and another an elevated lipase. Our data suggest that although the total serum amylase level is determined in part by the GFR, elevations in either amylase or lipase may not occur even in the presence of renal failure. Therefore, even small elevations in the total serum amylase or lipase in a patient with renal insufficiency may be clinically significant.

Low plasma free choline is prevalent in patients receiving long term parenteral nutrition and is associated with hepatic aminotransferase abnormalities

Hepatic transaminase abnormalities have been previously reported in patients receiving long term total parenteral nutrition (PN). We sought to determine if such abnormalities are caused by choline deficiency-induced hepatocyte damage. In 41 subjects (19 male, 22 female) aged 45.1 +/- 24.3 years (range 0.1-79 years) who have received PN for 5.5 +/- 4.7 years (range 0.1-14.5 years). We determined plasma free and phospholipid bound choline levels, serum albumin, ALT and AST. We also determined the daily volume of intravenous lipid emulsion received by the patients as well as the concentration of free choline and phospholipid bound choline in the lipid emulsion. Plasma free choline was low in 33 41 subjects (mean 7.15 +/- 2.5 nmol/ml, range 3.3-15.6, normal 11.4 +/- 3.7). Phospholipid bound choline was normal in 34 41 subjects (mean 2157 +/- 620 nmol/ml, range 1026-3887, normal 2364 +/- 774). Elevations in ALT and AST were significantly correlated with plasma free choline (r = -0.34, p = 0.03, r = -0.37, p = 0.02 respectively) but not with phospholipid bound choline. No relationship was found between age, PN duration or daily volume of intravenous lipid and plasma free or phospholipid bound choline. The lipid emulsion contained 24 +/- 6 nmol/ml of free choline and 11 630 +/- 552 nmol/ml of phospholipid bound choline. We conclude that low plasma free choline is prevalent in patients receiving long term PN and this abnormality is associated with elevated serum aminotransferases. Furthermore, intravenous lipid emulsion is an inadequate source of choline for this patient group.

Lecithin increases plasma free choline and decreases hepatic steatosis in long-term total parenteral nutrition patients

Plasma-free choline levels have previously been found below normal in patients receiving long term parenteral nutrition (TPN). In a group of 15 patients receiving home TPN who had low plasma free choline levels (6.3 +/- 0.8 mmol/L), we found 50% had hepatic steatosis. These patients were given oral lecithin or placebo in a double-blind randomized trial for 6 weeks. Lecithin supplementation led to an increase in plasma free choline of 53.4% +/- 15.4% at 2 weeks (P = 0.04), which continued at 6 weeks. The placebo group had no change in plasma-free choline at 2 weeks, but a significant decrease of 25.4% +/- 7.1% (P = 0.01) at 6 weeks. A significant and progressive decrease in hepatic fat was indicated by increased liver-spleen CT Hounsfield units at 2 and 6 weeks (7.5 +/- 1.7 units, P = 0.02; 13.8 +/- 3.5 units, P = 0.03) in the lecithin supplemental group. Nonsignificant changes were seen in the placebo group. It was concluded that hepatic steatosis in many patients receiving long term TPN is caused by plasma-free choline deficiency and may be reversed with lecithin supplementation. Choline is a conditionally essential nutrient in this population.

M-mode and two-dimensional echocardiography in the routine follow-up of central venous catheters in children receiving total parenteral nutrition

A retrospective study in 38 children (1 day to 7 years) on total parenteral nutrition (TPN) (1 month-24 months) with a central venous catheter (CVC) evaluated the contribution of two-dimensional echocardiography (2D) and M-mode in the follow-up of CVC location and early diagnosis of related complications. Fifty examinations were performed routinely in 21 patients (group I) and 40 in 17 patients for sepsis of the CVC or clinical suspicion of thrombosis (group II). The tip of the CVC was located in the upper right atrium in 17 cases (45%), superior vena cava in 14 cases (37%), jugular or subclavian vein in 5 cases (13%), and was not visualized in 2 cases (15%). In group I, 2D was normal in 19 cases, and catheter thrombosis suspected in 2 was not confirmed by digital angiography (DA). In group II, 2D was normal in 11 cases. In 6 patients, subxiphoid and suprasternal planes identified superior vena cava thrombus in the right atrium (DA confirmed the diagnosis in 2). In 2 pulmonary embolism occurred (1 case died); the remaining patients were successfully treated by medical therapy and removal of the catheter. Echocardiography is a useful noninvasive technique to control CVC tip location and follow-up. In this study, the sensitivity of cardiac thrombus detection by echocardiography was 100% and the specificity 93%; this method appeared, therefore, appropriate for early detection of cardiac thrombosis in pediatric patients on TPN.

Low blood and plasma carnitine levels in children receiving long-term parenteral nutrition

Total and free carnitine and acylcarnitine concentrations were analyzed in whole blood and plasma in 12 children with a mean age of 68.4 +/- 42.9 months who had received carnitine-free total parenteral nutrition (TPN) for an average of 4 years. The purpose of the study was to see if the children had become carnitine deficient and, if so, whether this correlated with poor lipid clearance. Compared to controls, the TPN-dependent children had significantly decreased concentrations of total and free carnitine in blood (26.6 +/- 9.4 (SD) mumols/L vs. 43.3 +/- 9.1 mumols/L, p less than 0.001, and 17.1 +/- 7.7 mumols/L vs. 35.2 +/- 8.1 mumols/L, p less than 0.001, respectively). Similar results were found in plasma (total carnitine of 19.0 +/- 8.0 mumols/L vs. 41.9 +/- 5.2 mumols/L, p less than 0.001, and free carnitine of 15.7 +/- 7.3 mumols/L vs. 36.1 +/- 5.2 mumols/L, p less than 0.001, respectively). The acylcarnitine concentration in plasma was decreased in the TPN children (3.3 +/- 1.5 mumols/L vs. 5.8 +/- 3.0 mumols/L, p less than 0.01) compared to controls. Despite the low carnitine concentrations, serum triglyceride levels and serum free fatty acid levels were within the normal range. There was no correlation between carnitine concentrations in plasma and serum triglyceride and free fatty acid levels. Our data show that children receiving carnitine-free TPN for many years developed markedly decreased concentrations of carnitine in blood and plasma. However, no adverse effects of the low carnitine levels were found on triglyceride and free fatty acid metabolism under stable conditions.

[Severe digestive manifestation of rheumatoid purpura. Retrospective study of 19 cases in children]

Digestive and/or nutritional manifestations of Henoch-Schoenlein purpura (HSP) in childhood may be so severe as to require nutritional assistance. The study of 19 cases with this form of the disease allows to suggest a therapeutic protocol. When enteral nutrition cannot be used from the onset, parenteral nutrition is required. Associated steroid therapy may prove helpful for the regression of the digestive signs. The observed slowness of the weight catch-up, in spite of high protein-energy intakes, emphasizes the severity of catabolism in these severe forms of HSP.