Gestational age-related reference values for amniotic fluid amino acids: a useful tool for prenatal diagnosis of aminoacidopathies

[Cystinuria]

Cystinuria is the most common monogenic nephrolithiasis disorder. Because of its poor solubility at a typical urine pH of less than 7, cystine excretion results in recurrent urinary cystine stone formation. A high prevalence of high blood pressure and of chronic kidney disease has been reported in these patients. Alkaline hyperdiuresis remains the cornerstone of the preventive medical treatment. To reach a urine pH between 7.5 and 8 and a urine specific gravity less than or equal to 1.005 should be the goal of medical treatment. D-penicillamine and tiopronin, two cysteine-binding thiol agents, should be considered as second line treatments with frequent adverse events that should be closely monitored.

Methylation metabolites in amniotic fluid depend on gestational age

OBJECTIVE

Methylation metabolism is essential for fetus development. However, normative data for amniotic fluid (AF) concentrations of methylation metabolites at different gestational ages are lacking. We aimed to determine in AF reference values of 14 intermediates involved in methylation.

METHODS

Two hundred sixty-eight AFs sampled between 14 and 39 weeks of gestation were retrospectively selected in our AF bank. Next, we measured methionine (Met)-cycle intermediates [S-adenosyl Met (AdoMet), S-adenosyl-l-homocysteine (AdoHcy), total Hcy, Met, and methyl malonic acid] and methyl donors and methyl acceptors (betaine, dimethylglycine, sarcosine, free and total choline, free and total ethanolamine, creatine, and guanidinoacetate) by liquid chromatography coupled with tandem mass spectrometry.

RESULTS

Reference ranges according to gestational age were determined for each parameter. Strong correlations between metabolites directly connected in their metabolic pathway and between total Hcy and betaine were observed.

CONCLUSION

Methionine, an essential amino acid required for protein synthesis, is the only parameter that dramatically decreases with gestational age. The AdoMet/AdoHcy ratio exponentially increases from 25 weeks of gestation, which could reflect increasing methylation capacities. The negative correlation between betaine and total Hcy together with a constant betaine to dimethylglycine ratio during gestation suggests that betaine may be used as a methyl donor during fetal life.

Correlation of 2nd trimester amniotic fluid amino acid profile with gestational age and estimated fetal weight

OBJECTIVES

Our aim was to identify and quantitate free amino acids in human amniotic fluid (AF) specimens collected during 2nd trimester amniocentesis and determine the correlation between amino acid concentrations, gestational age, and estimated fetal weight.

METHODS

Seventy-eight AF samples were retrieved between 18 and 22 weeks of gestation. Fetal weight estimation was based on fetal biometric measurements.

RESULTS

Twenty-one amino acids were quantified. The concentration of glutamine exhibited the greatest correlation with gestational age (r = 0.477, p < 0.01). Additionally, significant negative correlations were recorded between gestational age and levels of alanine, proline, lysine, valine, taurine, leucine, glutamic acid, tyrosine, phenylalanine, isoleucine, ornithine, methionine, and tryptophane (p < 0.05). After adjusting for maternal age, fetal gender, intervals between consecutive pregnancies, pre-pregnancy body mass index, and smoking during pregnancy the strength of the correlation for proline and lysine decreased. A stepwise multiple linear regression model including gestational age as a first level predictor of fetal weight indicated that lysine and cysteine concentrations were additional predictors.

CONCLUSIONS

Our results suggest that AF amino acids are crucial for fetal growth. Our purpose was not to establish an immediate diagnostic application. However, further exploration is likely to be fruitful, especially in high-risk pregnancies.

Mid-trimester amniotic fluid methionine concentrations: a predictor of birth weight and length

The association between body size at birth and risk of later cardiovascular disease is thought to be a consequence of metabolic changes that accompany slow growth in utero. The metabolism of methionine and homocysteine has been investigated in relation to cardiovascular risk and has also been assigned an important role in organogenesis and normal fetal growth. We determined concentrations of cobalamin, folate, methionine, cysteine, cystathionine, and the marker of B-vitamin function, homocysteine, in 625 samples of amniotic fluid obtained in the second trimester from normal pregnancies. Both vitamins and metabolites varied according to gestational age. The most noticeable observation was that methionine in amniotic fluid during gestational weeks 13 to 17 strongly predicted final birth weight and length. Metabolism of methionine may be a critical factor affecting fetal growth.

Isolated sulphite oxidase deficiency mimics the features of hypoxic ischaemic encephalopathy

Isolated sulphite oxidase deficiency (ISOD) is a rare autosomal recessive inborn error of metabolism, which may present at birth with intractable seizures (often of prenatal onset) and severe neurological abnormalities. In infants who survive, lens dislocation may occur from 8 weeks of age. The neuropathological findings in ISOD are similar to those seen in severe perinatal asphyxia. We describe two siblings with ISOD born to healthy non-consanguineous parents. The first child presented within 48 h of birth with poor feeding and seizures. He died from septicaemia on day 20 of life. The clinical presentation, neuroradiology and autopsy suggested a diagnosis of severe hypoxic ischaemic encephalopathy with a low recurrence risk. The second child presented with seizures within an hour of birth. She lived for 16 months during which time she failed to make developmental progress and continued to experience intractable seizures. Her neuroradiology was similar to her brother's. A diagnosis of ISOD was suggested from high urinary S-sulphocysteine in the second child and confirmed by the absence of sulphite oxidase activity in skin fibroblast culture. The diagnosis has enabled the couple to access prenatal testing in a subsequent pregnancy.

CONCLUSION

Isolated sulphite oxidase deficiency is an autosomal recessive condition which may mimic ischaemic encephalophathy. The disorder should be considered in all cases of intrauterine seizures, intractable seizures in the newborn period and infants with clinical and radiological features of ischaemic encephalophathy, especially when no obvious insult can be determined.

Isolated sulfite oxidase deficiency: a case report with a novel mutation and review of the literature

Isolated sulfite oxidase deficiency is a rare but devastating neurologic disease that usually presents in early infancy with seizures and alterations in muscle tone. Only 21 cases have been reported in the literature. We report a case of a newborn infant boy with isolated sulfite oxidase deficiency who presented with generalized seizures on his fourth day of life. Plasma total homocysteine was not detectable. Urinary sulfite, thiosulfate, and S-sulfocysteine levels were elevated. The patient began a low-methionine and low-cysteine diet and was treated with thiamine and dextromethorphan. However, he became increasingly microcephalic and was severely developmentally delayed. Mutation analysis of the sulfite oxidase gene revealed that the patient was homozygous for a novel 4-base pair deletion, and both of his parents were found to be heterozygous carriers of the same deletion. We reviewed the clinical, biochemical, neuroradiologic, and neuropathologic features in all published cases of isolated sulfite oxidase deficiency. Seizures or abnormal movements were prominent features in all cases. Developmental delays were reported in 17 cases. Ectopia lentis was detected in 9 cases. Clinical improvement with dietary therapy was seen in only 2 patients, both of whom presented after the age of 6 months and had relatively mild developmental delays. Plasma or urinary S-sulfocysteine levels were elevated in all cases. Urinary sulfite was detected in all except 1 case. Cerebral atrophy and cystic encephalomalacia were observed with neuroradiologic imaging and were noted in all 3 postmortem reports of isolated sulfite oxidase deficiency. The main alternative in the differential diagnosis of isolated sulfite oxidase deficiency is molybdenum cofactor deficiency.

A rapid and quantitative mass spectrometry method for determining the concentration of acylcarnitines and aminoacids in amniotic fluid

We describe a quantitative, rapid, sensitive and reproducible tandem mass spectrometry (MSMS) method for the one-step detection of aminoacid (AAs) and acylcarnitine (ACs) concentrations in amniotic fluid. This technology is quicker and more sensitive than other methods used to date since it is possible to determine very low AA and AC concentrations in samples simultaneously in a single run. The high degree of automation allows a large number of pregnancies to be screened for metabolic defects in a very short time.

Laboratory evaluation of urea cycle disorders

The urea cycle disorders (UCDs) represent a group of inherited metabolic diseases with hyperammonemia as the primary laboratory abnormality. Affected individuals may become comatose or die if not treated rapidly. Diagnosis of a UCD requires a high index of suspicion and judicious use of the laboratory. It is important to rule out other conditions causing hyperammonemia that may require different treatment. The astute clinician may suspect a specific UCD in the appropriate clinical setting, but only laboratory results can confirm a specific diagnosis. The importance of the laboratory in helping the clinician to differentiate among various causes of hyperammonemia, in confirming a specific UCD, in carrier testing, and in prenatal diagnostic testing is highlighted in this review.