Diagnosis of isovaleric acidaemia by tandem mass spectrometry: false positive result due to pivaloylcarnitine in a newborn screening programme

Tandem mass spectrometric analysis of acylcarnitines and amino acids has been applied in newborn screening programmes for the detection of several inborn errors of metabolism. We report a false positive result for isovaleric acidaemia in a newborn screening programme using this method. The newborn screening sample showed a very prominent signal corresponding to the mass of isovalerylcarnitine. Repeat samples (age 6 days) of blood and urine showed similar results. However, urine organic acids were normal. Acylcarnitine analysis in blood, breast milk and urine of the mother also showed a prominent signal of the same mass. Gas chromatography-mass spectrometry of the methyl esters demonstrated that the signal in the patient's urine was due to the presence of pivaloylcarnitine, which is isomeric with isovalerylcarnitine. The patient's mother was receiving an antibiotic containing a derivative of pivalic acid to treat a urinary tract infection. Follow-up samples in the patient and the mother confirmed a decrease in the levels of pivaloylcarnitine, concomitant with the discontinuation of the treatment. We conclude that pivaloylcarnitine can give a false positive result for isovaleric acidaemia in newborns whose mothers are on treatment with pivoxilsulbactam-containing antibiotics.

Response to nutritional and growth hormone treatment in progeria

Hutchinson-Gilford progeria syndrome (HGPS) is a rare condition with an unknown molecular defect. Patients with HGP progressively develop failure to thrive (FTT), alopecia, loss of subcutaneous fat, scleroderma, stiffening of various joints, and severe atherosclerosis. The median life span is 13 years, and the main cause of death is cardiovascular complications. There are few reports of endocrine and metabolic studies because of the rarity of this condition, and the response to long-term growth hormone (GH) treatment has not been described. We report the results of endocrine and metabolic studies performed to investigate the etiology of growth failure in five patients with HGP. Additionally, the response to nutritional therapy (NT) and GH treatment in three of these patients is presented. Our results suggest that elevated GH levels are characteristic of this disease and that an elevated basal metabolic rate (BMR) could be the cause of the FTT seen in HGP. Nonaggressive NT slightly improved weight gain and growth velocity (GV). Combined NT and GH treatment in three patients improved the GV, increased the levels of growth factors, and paradoxically resulted in decreased BMRs. However, the response to these therapies decreased over time and did not seem to prevent the progression of atherosclerotic disease.

Screening for the mitochondrial DNA A3243G mutation in children with insulin-dependent diabetes mellitus

Since recent studies demonstrated the occurrence of the mitochondrial DNA (mtDNA) mutation A3243G in patients with adult-onset diabetes, an investigation was undertaken to determine the frequency of this mutation in a pediatric population with insulin-dependent diabetes mellitus (IDDM). DNA was extracted from peripheral blood of 270 pediatric patients with IDDM. The presence of the mtDNA A3243G mutation was screened for by minisequencing and mutation-specific ApaI endonuclease restriction after polymerase chain reaction (PCR) amplification of mtDNA. The A3243G mtDNA mutation was not found in any IDDM patients examined. This mutation is uncommon in children with IDDM from various ethnic and racial groups. Therefore, the contribution of the mutation to the pathogenesis of IDDM, if any, is minimal.

Molecular prenatal diagnosis of glycogen storage disease type Ia

Glycogen storage disease type Ia (GSD Ia, von Gierke disease) is an autosomal recessive inborn error of metabolism caused by the deficiency of D-glucose-6-phosphatase (G6Pase). Since this enzyme is expressed primarily in hepatocytes, couples at risk for GSD type Ia relied on fetal liver biopsy for prenatal diagnosis. The recent isolation of the G6Pase gene and identification of several disease-causing mutations have permitted molecular prenatal diagnosis using amniocytes or chorionic villi. Chorionic villus sampling (CVS) was performed in an Ashkenazi Jewish family in whom a previous child was homoallelic and both parents were heterozygous for the R83C mutation. Molecular analysis revealed that the fetus was not affected. The prenatal diagnosis was confirmed postnatally by biochemical and molecular studies. Thus, the molecular prenatal diagnosis of GSD type Ia can be safely and accurately made in the first trimester.

Molecular prenatal diagnosis of glycogen storage disease type Ia

Glycogen storage disease type Ia (GSD Ia, von Gierke disease) is an autosomal recessive inborn error of metabolism caused by the deficiency of D-glucose-6-phosphatase (G6Pase). Since this enzyme is expressed primarily in hepatocytes, couples at risk for GSD type Ia relied on fetal liver biopsy for prenatal diagnosis. The recent isolation of the G6Pase gene and identification of several disease-causing mutations have permitted molecular prenatal diagnosis using amniocytes or chorionic villi. Chorionic villus sampling (CVS) was performed in an Ashkenazi Jewish family in whom a previous child was homoallelic and both parents were heterozygous for the R83C mutation. Molecular analysis revealed that the fetus was not affected. The prenatal diagnosis was confirmed postnatally by biochemical and molecular studies. Thus, the molecular prenatal diagnosis of GSD type Ia can be safely and accurately made in the first trimester.

[Autoimmune hypoglycemia syndrome with specific anti-human insulin antibodies]

A 33 year old woman with episodes of severe hypoglycemia is presented. The studies showed anti-insulin antibodies and variable C-peptide levels. Circulating insulin measured after acid-ethanol extraction, was of 1,600 uU/ml and shown to be human insulin after characterization by HLPC. Specific anti-human insulin antibodies were of high affinity (Ka1: 6.20 x 10(10) M-1; Ka2: 2.42 x 10(9) M-1). A small cross-reactive porcine and bovine antibody subpopulation was also detected (IgG, light k type chain). Plasmapheresis was undertaken when symptoms were spontaneously declining and turned antibody title negative. Prolonged follow-up showed no relapse of this syndrome.

Body composition and spontaneous growth hormone secretion in normal short stature children

This study was designed to compare the relationship of measured and estimated indices of adiposity with the spontaneous GH secretion (SGHS) in 37 normal short stature children. Fifteen of the 37 patients (10 males and 5 females) were pubertal, and 22 (17 males and 5 females) were prepubertal. All patients underwent a review of their medical history, a physical exam, laboratory tests, and a nutritional assessment that included anthropometry and evaluation of body composition by bioelectric impedance. The percentage of body fat and body fat mass index were used as measured indices of adiposity. The weight for height ratio, body mass index, and body mass index z-scores were calculated and used as estimated indices of adiposity. Our results showed that SGHS is greatly influenced by variations in adiposity in normal short stature children, and measured indices of adiposity demonstrated the strongest negative correlation with SGHS. Gender differences were apparent in the degree of adiposity that modified SGHS, and it appears that adiposity altered the amplitude of GH pulses in pubertal patients and the number of pulses in prepubertal children. These results suggest that interpretation of SGHS must take into account body composition and gender in addition to pubertal status.

Alterations in spontaneous growth hormone (GH) secretion and the response to GH-releasing hormone in children with nonorganic nutritional dwarfing

The effects of suboptimal nutrition on the spontaneous overnight GH secretion (SGHS) and the GH response to GHRH were studied. Sixteen patients with nonorganic nutritional dwarfing (ND) were compared with 25 healthy short children with familial short stature with or without constitutional growth delay (FC). The effects of puberty were also assessed. All patients underwent an overnight study to assess SGHS with serum GH levels sampled every 20 min for 12 h, and a GHRH stimulation test was administered. Pubertal ND children had a blunted SGHS with a mean overnight GH level of 4.9 +/- 1.1 micrograms/L, significantly less than the level of 6.2 +/- 1.8 micrograms/L of the pubertal FC children (P less than 0.05). Also, prepubertal ND patients had an area under the curve in GH secretion after GHRH which was greater than that of the pubertal ND patients (2483 +/- 1581 vs. 1600 +/- 1056, P less than 0.05). The peak GH response to GHRH in the prepubertal ND patients was also higher than that of the pubertal ND patients (51.8 +/- 22.1 micrograms/L vs. 22.5 +/- 15.4 micrograms/L, P less than 0.05). This study shows that the SGHS is attenuated in ND patients during puberty but their GH response to GHRH is increased before adolescence. These abnormalities may represent compensatory mechanisms to energy restriction and may increase our understanding of the poor growth seen in ND patients.