Prenatal diagnosis of citrullinemia and argininosuccinic aciduria: evidence for a transmission ratio distortion in citrullinemia

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.

Prevalence of the most common pathogenic variants in three genes for inborn errors of metabolism associated with sudden unexpected death in infancy: a population-based study in south Brazil

Citrullinemia type 1 (CTLNI), long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency (LCHADD), and mut⁰ methylmalonic acidemia (mut⁰ MMA) are inborn errors of metabolism (IEMs) associated with sudden unexpected death in infancy (SUDI). Its most common pathogenic variants are: c.1168G>A (CTLNI, ASS1 gene), c.1528G>C (LCHADD, HADHA gene), c.655A>T and c.1106G>A (mut⁰ MMA, MUT gene). Considering the absence of estimates regarding the incidence of these diseases in Brazil, this study sought to investigate the prevalence of its main pathogenic variants in a healthy population in the southern region of the country. A total of 1,000 healthy subjects from Rio Grande do Sul were included. Genotyping was performed by real-time PCR. Individuals found to be heterozygous for c.1528G>C underwent further acylcarnitine profile analysis by tandem mass spectrophotometry. Allele and genotype frequencies were calculated considering Hardy-Weinberg equilibrium. The c.1528G>C variant was detected in heterozygosity in two subjects (carrier frequency = 1:500; allele frequency = 0.001; minimum prevalence of LCHADD = 1: 1,000,000), whose acylcarnitine profiles were normal. Variants c.1168G>A, c.655A>T, and c.1106G>A were not identified. These results denote the rarity of these IEMs in Southern Brazil, highlighting the need to expand the investigation of IEMs in relation to infant morbidity and mortality within the country.

Urea cycle disorders in Argentine patients: clinical presentation, biochemical and genetic findings

Background

The incidence, prevalence, and molecular epidemiology of urea cycle disorders (UCDs) in Argentina remain underexplored. The present study is the first to thoroughly assess the clinical and molecular profiles of UCD patients examined at a single reference center in Argentina.

Results

Forty-nine UCD cases were collected. About half (26/49, 53%) manifested neonatally with classical presentation and had a high mortality (25/26, 96%). Ornithine transcarbamylase deficiency (OTCD) was the most common UCD (26 patients). Argininosuccinate synthetase deficiency (ASSD) was detected in 19 cases, while argininosuccinate lyase deficiency (ASLD) was diagnosed in 4 cases. Molecular genetic analysis revealed 8 private OTC mutations and two large deletion/duplication events in the OTC gene. Most mutations in the ASS1 and ASL genes were recurrent missense changes, and four alterations were novel. The clinical outcome of our UCD cohort was poor, with an overall mortality of 57% (28/49 cases), and a 28% (6/21) disability rate among the survivors.

Conclusions

Most patients in our case series showed severe neonatal onset, with high morbidity/mortality. We detected in total 19 mutations, most of them recurrent and of high frequency worldwide. Noteworthy, we highlight the presence of a geographic cluster with high prevalence of a point mutation in the ASS1 gene. This study suggests that these disorders may be more frequent than commonly assumed, and stresses the need for increased awareness amongst health professionals and greater availability of diagnostic tools for accurate identification, early diagnosis, and timely treatment.

Electronic supplementary material

The online version of this article (10.1186/s13023-019-1177-3) contains supplementary material, which is available to authorized users.

Urea cycle disorders in India: clinical course, biochemical and genetic investigations, and prenatal testing

Background

Urea cycle disorders (UCDs) are inherited metabolic disorders that present with hyperammonemia, and cause significant mortality and morbidity in infants and children. These disorders are not well reported in the Indian population, due to lack of a thorough study of the clinical and molecular profile.

Results

We present data from two major metabolic centres in India, including 123 cases of various UCDs. The majority of them (72/123, 58%) presented in the neonatal period (before 30 days of age) with 88% on or before day 7 of life (classical presentation), and had a high mortality (64/72, 88%). Citrullinemia type 1 was the most common UCD, observed in 61/123 patients. Ornithine transcarbamylase (OTC) deficiency was the next most common, seen in 24 cases. Argininosuccinic aciduria was diagnosed in 20 cases. Deficiencies of arginase, N-acetylglutamate synthase, carbamoyl phosphate synthetase, citrin, and lysinuric protein intolerance were also observed.

Molecular genetic analysis revealed two common ASS1 mutations: c.470G > A (p.Arg157His) and c.1168G > A (p.Gly390Arg) (36 of 55 tested patients). In addition, few recurrent point mutations in ASL gene, and a deletion of the whole OTC gene were also noted. A total of 24 novel mutations were observed in the various genes studied. We observed a poor clinical outcome with an overall all time mortality of 63% (70/110 cases with a known follow-up), and disability in 70% (28/40) among the survivors. Prenatal diagnosis was performed in 30 pregnancies in 25 families, including one pre-implantation genetic diagnosis.

Conclusions

We report the occurrence of UCDs in India and the spectrum that may be different from the rest of the world. Citrullinemia type 1 was the most common UCD observed in the cohort. Increasing awareness amongst clinicians will improve outcomes through early diagnosis and timely treatment. Genetic diagnosis in the proband will enable prenatal/pre-implantation diagnosis in subsequent pregnancies.

Electronic supplementary material

The online version of this article (10.1186/s13023-018-0908-1) contains supplementary material, which is available to authorized users.

Kinetic mutations in argininosuccinate synthetase deficiency: characterisation and in vitro correction by substrate supplementation

BACKGROUND

Citrullinemia type 1 is an autosomal-recessive urea cycle disorder caused by mutations in the ASS1 gene and characterised by increased plasma citrulline concentrations. Of the ∼90 argininosuccinate synthetase (ASS) missense mutations reported, 21 map near the substrate (aspartate or citrulline) binding site, and thus are potential kinetic mutations whose decreased activities could be amenable to substrate supplementation. This article aims at characterising these 21 ASS mutations to prove their disease-causing role and to test substrate supplementation as a novel therapeutic approach.

METHODS

We used an Escherichia coli expression system to study all potentially kinetic ASS mutations. All mutant enzymes were nickel-affinity purified, their activity and kinetic parameters were measured using tandem mass spectrometry and their thermal stability using differential scanning fluorimetry. Structural rationalisation of the effects of these mutations was performed.

RESULTS

Of the characterised mutants, 13 were totally inactive while 8 exhibited decreased affinity for aspartate and citrulline. The activity of these eight kinetic mutations could be rescued to ∼10-99% of the wild-type using high l-aspartate concentrations.

CONCLUSIONS

Substrate supplementation raised in vitro the activity of eight citrullinemia type 1 mutations with reduced affinity for aspartate. As a direct translation of these results to the clinics, we propose to further evaluate the use of oxaloacetate, a nitrogen-free aspartate precursor and already available medical food (anti-ageing and brain stimulating, not considered as a drug by the US Food and Drug Administration), in patients with citrullinemia type 1 with decreased aspartate affinity. Although only patients with kinetic mutations would benefit, oxaloacetate could offer a safe novel treatment.

Dynamic monitoring of plasma amino acids and carnitine during chemotherapy of patients with alimentary canal malignancies and its clinical value

OBJECTIVE

The aim of this study was to observe the plasma amino acid and carnitine characteristics in patients with metastatic gastrointestinal malignancies during chemotherapy and to identify markers for the early diagnosis and evaluation of adverse reactions and prognosis of the digestive tract malignant tumor patients.

METHODS

Blood samples of 30 patients with metastatic gastrointestinal malignancies were collected at four time points: before chemotherapy, the first day after chemotherapy (+1 day), bone marrow depression period (+14 days), and hematopoietic recovery period (+21 days). The plasma amino acids and carnitine from those 30 patients were determined by high-performance liquid chromatography-tandem mass spectrometry method. Simultaneously, the levels of 21 amino acids were detected in 30 healthy individuals, who were considered as control. Biochemical indexes were also detected at four time points, adverse reactions were recorded during the chemotherapy process, and patients were followed up for 1 year to observe time to progression (TTP) and progression-free survival (PFS).

RESULTS

Compared to healthy people in the control group, patients with malignancies showed significantly increased levels of plasma amino acids such as Arg, Asp, Cit, Gly, Orn, Tyr, Val, and carnitine (such as C2). The levels of compounds such as C3, Asn, Leu, Lys, Pip, Pro, C0, C5:1 decreased significantly before chemotherapy. The levels of Cit, Cys, Lys, Pro, Tyr, Val, C0, and C2 decreased significantly on the second day of chemotherapy (+1 day), whereas the level of C3 increased significantly. During myelosuppression (+14 days), the levels of Asp, Cit, Met, and Orn were observed to still decrease significantly, whereas the level of Val appeared to increase significantly. The levels of Asp, Glu, and Met were clearly different among patients with gastric carcinoma, rectal cancer, and colon cancer. Compared to the control group, aspartate amino transferase and alanine aminotransferase were found to be higher in eight patients with hypocarnitinemia, yet TTP, PFS, and RR (response rate) were lower. No significant difference was observed for adverse reactions. The indexes in 12 patients with citrullinemia showed no difference compared with control group. All the results showed statistically significant differences (P<0.05).

CONCLUSION

Real-time monitoring of plasma amino acids and carnitine in patients with metastatic gastrointestinal malignancies can directly reflect the body's metabolism and nutritional status. The results provide a reference for nutrition therapy or support for patients with alimentary canal malignancies. Hypocarnitinemia is a risk factor for gastrointestinal cancer patients and affects TTP, PFS, and RR by liver function. This study shows that tandem mass spectrometry can be used to detect blood amino acids and carnitine spectrum may be used for an early diagnosis and evaluation of adverse reactions and prognosis of the digestive tract malignant tumor patients.

Improved standards for prenatal diagnosis of citrullinemia

Citrullinemia type I is a urea cycle disorder caused by autosomal recessive mutations in argininosuccinate synthetase 1 (ASS1). In the classical form of this disease, symptoms manifest during the neonatal period as progressive lethargy, poor feeding, and central nervous system depression secondary to hyperammonemia. In pregnancies involving two carrier parents, prenatal diagnosis is important for both reproductive decisions and advanced preparation for neonatal care. The current gold standard for prenatal diagnosis has been the citrulline incorporation assay in addition to DNA mutation analysis. Herein, we review our experience with prenatal diagnosis of citrullinemia type I over the span of 11 years in 41 at-risk pregnancies. During this time, we identified 15 affected fetuses using a combination of molecular and biochemical testing. Given the established limitations of both the citrulline incorporation assay as well DNA mutation analysis, we probed our data to assess the value of amniotic fluid amino acid levels in prenatal diagnosis. Previous publications have proposed using the amniotic fluid ratio of citrulline/(arginine+ornithine) in prenatal diagnosis; however, we noted that amniotic fluid arginine levels were normal in our cohort and hypothesized that the amniotic fluid citrulline/ornithine ratio may be superior. Indeed, our analyses revealed that the ratio of amniotic fluid citrulline/ornithine alone correctly distinguished affected from unaffected fetuses in all cases. During the establishment of a normal reference range we discovered significant elevations in amniotic fluid citrulline levels in at-risk pregnancies compared to the normal population even when the fetus was unaffected. This highlights the importance of using amniotic fluid from carrier mothers when setting up a normal reference range. Finally, we report our experience as one of the first centers to adopt Sanger sequencing for prospective prenatal diagnosis of citrullinemia. While this is clearly a useful tool in many cases, we encountered families for whom molecular analysis uncovered variants of unknown clinical significance or no mutation at all. Based upon these new findings, we recommend a combinatorial approach involving ASS1 sequencing and amniotic fluid citrulline/ornithine for the prenatal diagnosis of citrullinemia type I.

Prenatal diagnosis of citrullinemia type 1: a Chinese family with a novel mutation of the ASS1 gene

BACKGROUND

Argininosuccinate synthetase deficiency (citrullinemia type 1) is a rare autosomal recessive disorder of the urea cycle characterized by elevated concentrations of citrulline, ammonia, and orotic acid, manifesting with acute hyperammonemic crises, usually early in life, with concurrent neurologic deterioration. Only a few cases of citrullinemia type 1 have been documented from mainland China. Prenatal diagnosis has not been performed.

METHODS

A Chinese family affected by citrullinemia type 1 was studied. The proband, a girl, was the second child born to a non-consanguineous couple. Her elder brother died at 19months due to coma and liver dysfunction of unknown cause. The proband was admitted because of severe mental retardation and lethargy at the age of 15months. Initial laboratory results revealed hyperammonaemia, hypercitrullinemia (928.771μmol/L, normal 5.0-25.0μmol/L) and orotic aciduria, supporting the diagnosis of citrullinemia type 1. Subsequently, the mother presented at 15weeks of pregnancy seeking for genetic counseling and prenatal diagnosis. ASS1 gene in the blood leukocytes of the family members and amniocytes was performed by direct sequencing.

RESULTS

On the ASS1 gene of the proband, a novel mutation, T1009C (C337R), and a previously reported mutation G847A (E283K) were identified. Each parent carries one of two mutations. G847A and T1009C mutations were detected in amniocytes, as same as the proband of the family. The result revealed that the fetus was affected by argininosuccinate synthetase deficiency. The parents chose to have a termination of the pregnancy.

CONCLUSIONS

Prenatal diagnosis for citrullinemia type 1 was performed in a Chinese family using gene analysis. T1009C (C337R), a novel mutation of ASS1, was identified.

Molecular epidemiology of citrullinemia type I in a risk region of Argentina: a first step to preconception heterozygote detection

Classical citrullinemia type I (CTLN1) is an autosomal recessive disorder encoded by the ASS1 gene, which codes for argininosuccinate synthetase (ASS), the rate-limiting enzyme in the urea cycle. Previously, we identified the mutation p.G390R in patients with CTLN1 in the San Luis Province of Argentina. Here, we report the results of p.G390R analysis in a larger number of probands, relatives of involved families and additionally, a population study to identify carriers. Altogether, we analyzed 420 alleles, belonging to 12 probands, 26 relatives, and 172 healthy volunteers. All the probands were homozygous for the mutation, and 21 of 26 relatives were carriers. The occurrence of the disease in descendants of couples at risk was 57% showing a preferential transmission of the mutant allele compared to the normal allele. The carrier frequency in the general San Luis Province population was 4.1%, suggesting the incidence of CTLN1 to be 1:2,427, which is approximately 20 times higher than for the general population. This work suggests that there should be an increased awareness of preconceptual screening of CTNL1 among individuals/couples who are at risk in the San Luis Province in order to better inform them of their reproductive options.Cascade/family and population molecular screening for carrier identification were performed in an Argentinean province with high incidence of CTLN1, a first step to preconceptional screening.

Argininosuccinate lyase deficiency

The urea cycle consists of six consecutive enzymatic reactions that convert waste nitrogen into urea. Deficiencies of any of these enzymes of the cycle result in urea cycle disorders (UCDs), a group of inborn errors of hepatic metabolism that often result in life-threatening hyperammonemia. Argininosuccinate lyase (ASL) catalyzes the fourth reaction in this cycle, resulting in the breakdown of argininosuccinic acid to arginine and fumarate. ASL deficiency (ASLD) is the second most common UCD, with a prevalence of ~1 in 70,000 live births. ASLD can manifest as either a severe neonatal-onset form with hyperammonemia within the first few days after birth or as a late-onset form with episodic hyperammonemia and/or long-term complications that include liver dysfunction, neurocognitive deficits, and hypertension. These long-term complications can occur in the absence of hyperammonemic episodes, implying that ASL has functions outside of its role in ureagenesis and the tissue-specific lack of ASL may be responsible for these manifestations. The biochemical diagnosis of ASLD is typically established with elevation of plasma citrulline together with elevated argininosuccinic acid in the plasma or urine. Molecular genetic testing of ASL and assay of ASL enzyme activity are helpful when the biochemical findings are equivocal. However, there is no correlation between the genotype or enzyme activity and clinical outcome. Treatment of acute metabolic decompensations with hyperammonemia involves discontinuing oral protein intake, supplementing oral intake with intravenous lipids and/or glucose, and use of intravenous arginine and nitrogen-scavenging therapy. Dietary restriction of protein and dietary supplementation with arginine are the mainstays in long-term management. Orthotopic liver transplantation (OLT) is best considered only in patients with recurrent hyperammonemia or metabolic decompensations resistant to conventional medical therapy.

Argininosuccinate lyase deficiency-argininosuccinic aciduria and beyond

The urea cycle consists of six consecutive enzymatic reactions that convert waste nitrogen into urea. Deficiencies of any of these enzymes of the cycle result in urea cycle disorders (UCD), a group of inborn errors of hepatic metabolism that often result in life threatening hyperammonemia. Argininosuccinate lyase (ASL) is a cytosolic enzyme which catalyzes the fourth reaction in the cycle and the first degradative step, that is, the breakdown of argininosuccinic acid to arginine and fumarate. Deficiency of ASL results in an accumulation of argininosuccinic acid in tissues, and excretion of argininosuccinic acid in urine leading to the condition argininosuccinic aciduria (ASA). ASA is an autosomal recessive disorder and is the second most common UCD. In addition to the accumulation of argininosuccinic acid, ASL deficiency results in decreased synthesis of arginine, a feature common to all UCDs except argininemia. Arginine is not only the precursor for the synthesis of urea and ornithine as part of the urea cycle but it is also the substrate for the synthesis of nitric oxide, polyamines, proline, glutamate, creatine, and agmatine. Hence, while ASL is the only enzyme in the body able to generate arginine, at least four enzymes use arginine as substrate: arginine decarboxylase, arginase, nitric oxide synthetase (NOS) and arginine/glycine aminotransferase. In the liver, the main function of ASL is ureagenesis, and hence, there is no net synthesis of arginine. In contrast, in most other tissues, its role is to generate arginine that is designated for the specific cell's needs. While patients with ASA share the acute clinical phenotype of hyperammonemia, encephalopathy, and respiratory alkalosis common to other UCD, they also present with unique chronic complications most probably caused by a combination of tissue specific deficiency of arginine and/or elevation of argininosuccinic acid. This review article summarizes the clinical characterization, biochemical, enzymatic, and molecular features of this disorder. Current treatment, prenatal diagnosis, diagnosis through the newborn screening as well as hypothesis driven future treatment modalities are discussed.

Mutations and polymorphisms in the human argininosuccinate synthetase (ASS1) gene

Citrullinemia type I is an autosomal recessive disorder that is caused by a deficiency of the urea cycle enzyme argininosuccinate synthetase (ASS1). Deficiency of ASS1 shows various clinical manifestations encompassing severely affected patients with fatal neonatal hyperammonemia as well as asymptomatic individuals with only a biochemical phenotype. This is a comprehensive report of all 87 mutations found to date in the ASS1 gene on chromosome 9q34.1. A large proportion of the mutations (n=27) are described here for the first time. Mutations are distributed throughout exons 3 to 15, most of them being identified in exons 5, 12, 13, and 14. The mutation G390R in exon 15 is the single most common mutation in patients with the classical phenotype. Certain mutations clearly link to specific clinical courses but the clinical phenotype cannot be anticipated in all patients. This update presents a survey of the correlation between mutations in the ASS1 gene and the respective clinical courses as described so far. It also sheds light on the geographic incidence of the mutations. Enzymatic studies have been done in bacterial and human cell systems. However, the prognostic value of genetic aberrations with respect to their effect on protein function and clinical manifestation remains uncertain.

Transmission ratio distortion at the growth hormone gene (GH1) in bovine preimplantation embryos: An in vitro culture-induced phenomenon?

The growth hormone gene (GH1) and its polypeptide product (GH) have a crucial role in reproduction, embryogenesis and general development. A polymorphism present in the fifth exon of the bovine GH1 gene (GH1 p.Leu127Val) has been associated with GH release and milk production in cattle. The objective of the present study was to examine the genotype frequencies of the GH1 p.Leu127Val polymorphism in bovine blastocysts produced in vitro and in vivo to determine if allelic variation of the GH1 gene affects embryo development and survival. A heterozygous (p.Leu127/Val127) sire was used for in vitro fertilization of oocytes of unknown maternal genotype (n = 104) and known maternal genotype (n = 115). PCR amplification and genotyping of the GH1 gene from Day 8 blastocysts derived from these fertilized oocytes demonstrated that there was significant over-representation from the expected Mendelian ratio of GH1 p.Leu127/Leu127 homozygotes from oocytes of known maternal genotype (P = 0.006). Contrary to this, analysis of in vivo-produced bovine blastocysts of known parental GH1 genotype (n = 69) did not reveal an overrepresentation of GH1 p.Leu127/Leu127 homozygotes. These results suggest that developing in vitro-produced embryos are exposed to a selection process, probably due to a less favorable culture environment, that acts to increase the number of GH1 p.Leu127/Leu127 homozygotes, thereby giving rise to the observed transmission ratio distortion (TRD) of GH1 genotypes when compared to in vivo produced embryos.

Prenatal diagnosis of some metabolic diseases using early amniotic fluid samples: report of a 15 years, experience

BACKGROUND

In the present study, we report the results of 132 prenatal diagnoses performed on chorionic villi and cell-free amniotic fluid obtained simultaneously at 12-13 weeks of gestation. In addition, we report the result of 59 prenatal diagnoses performed at 12-13th week using amniotic fluid only.

METHODS AND RESULTS

A total of one fetal loss (1/191) was observed when a sample of amniotic fluid was obtained at around 12-13 weeks, whereas three losses (3/82) were observed after midtrimester amniocentesis. We attribute this finding to the fact that only a very small volume of amniotic fluid was sampled using a very small needle.

CONCLUSION

From these data it appears that when a couple is facing a high risk of recurrence of some metabolic diseases, the study of chorionic villus and amniotic fluid sampled simultaneously offers a safe and reliable method of early prenatal diagnosis.