Medium Chain Acyl-CoA Dehydrogenase Deficiency (MCADD) in the Irish Paediatric Population.

Aim This study aims to investigate the disease frequency of Medium Chain Acyl-CoA Dehydrogenase Deficiency (MCADD) among the Irish population. Methods Children (<18 years) with MCADD were identified via the National Centre for Inherited Metabolic Disorders and the metabolic laboratory at Temple Street Children's University Hospital. Central Statistics Office population data was used to calculate epidemiological figures. Results From 1998 to 2016, 17 children (<18 years) were diagnosed with MCADD including two patients whose initial presentation was fatal. The mean age at initial presentation was 1.48 years (Range: 0.005 to 2.86). The incidence was 1:71650 with mortality at 15.38%. No child subsequently died post diagnosis. The common c.985A>G mutation accounted for 88% of alleles. Conclusion The incidence of MCADD in Ireland is lower than global estimates. The potential for under-ascertainment and late diagnosis of cases exists in Ireland and is of concern for a treatable condition with a significant mortality when undiagnosed. The authors welcome the introduction of MCADD to the National Newborn Bloodspot Screening Program.

'Malignant Phenylketonuria' (PKU) Due to Dihydropteridine Reductase (DHPR) Deficiency.

DHPR deficiency is a rare autosomal recessively inherited metabolic disorder of tetrahydrobiopterin (BH4) regeneration. Clinical symptoms may comprise microcephaly, developmental delay, ataxia and seizures. BH4 is the cofactor for the enzyme phenylalanine (Phe)hydroxylase (PAH), and for tryptophan and tyrosine hydroxylases, both of which are essential for serotonin and dopamine biosynthesis. We present four patients in two families who are being treated at the National Centre for Inherited Metabolic Disorders (NCIMD). All are members of the Irish Traveller population. We have identified a homozygous mutation, c.353C>T, in the DHPR (QDPR) gene which, to the best of our knowledge, has not been previously described. The mainstay of treatment is a life-long Phe-restricted diet together with supplementation of L-dopa and 5-hydroxy tryptophan (5-HT) and folinic acid. In Ireland, there is neurological comorbidity in our adult DHPR patients, although the overall outcome is satisfactory and one affected female has three healthy children.

Classical Galactosaemia in Ireland: incidence, complications and outcomes of treatment.

Newborn screening for the inborn error of metabolism, classical galactosaemia prevents life-threatening complications in the neonatal period. It does not however influence the development of long-term complications and the complex pathophysiology of this rare disease remains poorly understood. The objective of this study was to report the development of a healthcare database (using Distiller Version 2.1) to review the epidemiology of classical galactosaemia in Ireland since initiation of newborn screening in 1972 and the long-term clinical outcomes of all patients attending the National Centre for Inherited Metabolic Disorders (NCIMD). Since 1982, the average live birth incidence rate of classical galactosaemia in the total Irish population was approximately 1:16,476 births. This reflects a high incidence in the Irish 'Traveller' population, with an estimated birth incidence of 1:33,917 in the non-Traveller Irish population. Despite early initiation of treatment (dietary galactose restriction), the long-term outcomes of classical galactosaemia in the Irish patient population are poor; 30.6 % of patients ≥ 6 yrs have IQs <70, 49.6 % of patients ≥ 2.5 yrs have speech or language impairments and 91.2 % of females ≥ 13 yrs suffer from hypergonadotrophic hypogonadism (HH) possibly leading to decreased fertility. These findings are consistent with the international experience. This emphasizes the requirement for continued clinical research in this complex disorder.

The role of human demographic history in determining the distribution and frequency of transferase-deficient galactosaemia mutations.

Classical or transferase-deficient galactosaemia is an inherited metabolic disorder caused by mutation in the human Galactose-1-phosphate uridyl transferase (GALT) gene. Of some 170 causative mutations reported, fewer than 10% are observed in more than one geographic region or ethnic group. To better understand the population history of the common GALT mutations, we have established a haplotyping system for the GALT locus incorporating eight single nucleotide polymorphisms and three short tandem repeat markers. We analysed haplotypes associated with the three most frequent GALT gene mutations, Q188R, K285N and Duarte-2 (D2), and estimated their age. Haplotype diversity, in conjunction with measures of genetic diversity and of linkage disequilibrium, indicated that Q188R and K285N are European mutations. The Q188R mutation arose in central Europe within the last 20 000 years, with its observed east-west cline of increasing relative allele frequency possibly being due to population expansion during the re-colonization of Europe by Homo sapiens in the Mesolithic age. K285N was found to be a younger mutation that originated in Eastern Europe and is probably more geographically restricted as it arose after all major European population expansions. The D2 variant was found to be an ancient mutation that originated before the expansion of Homo sapiens out of Africa.

Thyroid dysfunction in Down's syndrome and screening for hypothyroidism in children and adolescents using capillary TSH measurement.

UNLABELLED: Thyroid dysfunction is more common in individuals with Down's syndrome (DS) than in the general population, whose clinical features can mask the presenting signs and symptoms of hypothyroidism. Biochemical screening is necessary; however, venepuncture may be difficult. AIMS: To assess the prevalence of thyroid dysfunction in children and adolescents with DS and the feasibility of screening for hypothyroidism using capillary dried blood spot thyroid stimulating hormone (TSH) from infancy. METHODS: 394 children (217 boys, 177 girls) were clinically assessed for thyroid dysfunction and 305 children (aged 4 months to 18.9 years) were screened for hypothyroidism by capillary whole blood TSH sample. RESULTS: Thyroid dysfunction was detected in 4.6%, with 50% unscreened since neonatal screening. Parents reported minimal distress by fingerprick screening. CONCLUSION: DS is associated with an increased prevalence of thyroid dysfunction, particularly in preschool children. Biochemical screening is essential and capillary whole blood TSH sampling for hypothyroidism is feasible, less invasive and acceptable.

Susceptibility of pregnant women to toxoplasma infection--potential benefits for newborn screening.

Congenital toxoplasmosis (CT) arises as a result of new acquisition of Toxoplasma infection by a susceptible woman during pregnancy. Early detection of CT through neonatal screening programmes could optimize management and improve infant outcome. This study sought to estimate the prevalence of Toxoplasma susceptibility in pregnant women. As detection of Toxoplasma antibodies in neonatal blood reflects maternal exposure history, maternal antibody seroprevalence was determined using anonymized residual blood from newborn screening cards. A total of 20,252 cards were tested in 1 year. 4,991 (24.6%) cards tested positive for Toxoplasma antibody. Results were stratified by county. Toxoplasma antibody seroprevalence rates of 25% indicated that Toxoplasma infection is common in Ireland and that up to 75% of women remain susceptible to primary infection during pregnancy. This study aimed to a) determine the seroprevalence of Toxoplasma antibody in pregnant women, and hence b) estimate the risk for acquisition of primary toxoplasmosis in pregnancy in order to support an application to fund a pilot newborn screening programme.

Mitochondrial cytopathies, phenotypic heterogeneity and a high incidence.

Mitochondrial respiratory chain disorders account for significant and varied presentations in paediatric practice. The true prevalence of these disorders in the paediatric population is still not well documented with predicted geographic variation. We report a retrospective analysis over a seven year period of cases presenting to a tertiary care centre and associated clinical features. The overall prevalence of mitochondrial disorders in our population is higher than expected (1/9,000 births), explained in part by multiple presentations in a consanguineous subgroup of the population (Irish travellers).

Unexplained developmental delay/learning disability: guidelines for best practice protocol for first line assessment and genetic/metabolic/radiological investigations.

BACKGROUND: Investigation of patients, particularly children, with unexplained global developmental delay (GDD)/learning disability (LD) has been challenging due to a lack of clear guidance from specialised centres. Limited knowledge of rare diseases and a poor understanding of the purpose or limitations of appropriate investigations have been some of the principal reasons for this difficulty. AIMS: A guideline development group was formed to recommend on appropriate, first line metabolic, genetic and radiological investigations for children and adults with unexplained GDD/ID. METHODS AND RECOMMENDATIONS: A comprehensive literature search was conducted, evaluated and reviewed by the guideline committee and a best practice protocol for first line assessment and genetic, metabolic and radiological investigations was decided upon after considering diagnostic yield, practicality, treatability and costs. CONCLUSION: It is hoped that these recommendations will become national guidelines for the first line metabolic, genetic and radiological investigation of patients presenting with unexplained GDD/ID.

Rapid detection of the R408W and I65T mutations in phenylketonuria by glycosylase mediated polymorphism detection.

Mutation detection methods based upon chemical or enzymatic cleavage of DNA offer excellent detection efficiencies coupled with high throughput and low unit cost. We describe the application of the novel technique of Glycosylase Mediated Polymorphism Detection (GMPD) to the detection of two of the most common mutations of the PAH gene in the Irish population that cause phenylketonuria (PKU), R408W and I65T, which occur at relative frequencies of 41.0% and 10.4% respectively. GMPD assays for R408W and I65T were developed permitting fluorescent detection of cleavage products on the ALFexpresstrade mark automated DNA sequencer. The method was validated by screening a panel of PKU patients whose mutant genotypes had previously been characterised by standard methods. It also proved possible to perform multiplex detection of the two mutations by co-electrophoresis of GMPD products. GMPD is a rapid and robust method for the detection of the R408W and I65T mutations, whose key advantage lies in its use of a pair of enzymes with high cleavage efficiency to detect a number of mutations as compared to the use of individual digestions with a range of specific restriction endonuclease enzymes. Hum Mutat 17:432, 2001.

Cholesterol-lowering drug therapy in a patient with receptor-negative homozygous familial hypercholesterolaemia.

Familial hypercholesterolaemia (FH) is caused by mutations in the gene for the low density lipoprotein (LDL) receptor. It is generally believed that homozygous FH patients do not respond well to lipid-lowering drug therapy with inhibitors of 3-hydroxy-3-methylglutaryl CoA reductase because they cannot respond to an increased demand for hepatic cholesterol by up-regulation of LDL-receptor activity. In this paper we show that serum cholesterol in a homozygous FH patient with a receptor-negative LDL-receptor phenotype was reduced by 30% after treatment with simvastatin alone and by a further 11% with simvastatin in combination with probucol and nicotinic acid. The patient was a true homozygote, with two identical alleles of the LDL receptor gene in which a previously undescribed point mutation in exon 11 introduces a premature termination codon at residue 540 in the protein; the mutant protein is predicted to be truncated in the domain with homology to the epidermal growth factor precursor. Cultured cells from the patient were unable to bind, internalise or degrade LDL by the receptor pathway and there was no immunodetectable LDL receptor protein in the cells. Thus the lipid lowering effect of simvastatin in this individual must involve mechanisms other than stimulation of LDL receptors.

Factor V Leiden (Arg506Gln), a confounding genetic risk factor but not mandatory for the occurrence of venous thromboembolism in homozygotes and obligate heterozygotes for cystathionine beta-synthase deficiency.

Thrombosis is the major cause of morbidity and mortality in individuals with untreated classical homocystinuria (HCU) due to cystathionine beta-synthase deficiency and characterised by severe hyperhomocysteinaemia. In addition, mild and moderate hyperhomocysteinaemia and Factor V Leiden (FVL; Arg506Gln) have recently been identified as thrombotic risk factors. FVL. which renders resistance to activated Protein C, is the most common inherited genetic risk factor for thrombosis with a high allelic frequency amongst Caucasians. As thrombophilia is a multigenic disorder, 26 individuals with HCU (median age 17.6 years, range 3.5-32.8 years) and 36 obligate heterozygotes (median age 51.5 years, range 34-74 years) were screened for FVL. All the HCU individuals received treatment, except one, within 6 weeks of birth for those who were diagnosed at birth through the national newborn screening programme (n = 20) and at the time of diagnosis for those late detected (n = 5, mean age of starting treatment 4.9 years, range 1.4-11 years). All had been free from venous thrombosis, except one HCU individual and one HCU obligate heterozygote. Neither of the two individuals with venous thrombosis carried FVL. Two independent individuals with HCU (male 14.8 years; female 18.2 years) were heterozygous for FVL (allelic frequency 3.8%) and three independent HCU obligate heterozygotes (males 40 and 45.8 years; female 45.6 years) were also heterozygous for FVL (allelic frequency 4.16%). The findings in this small group suggest that FVL is not a mandatory but a significant confounding risk factor for the occurrence of thrombosis in HCU individuals and additional contributing factors may be required for thrombosis to occur in HCU obligate heterozygotes with FVL heterozygosity. Our data also suggest that treatment of HCU not only reduces the thrombotic risk in patients with isolated HCU but also in those with the additional FVL heterozygosity.

Methylenetetrahydrofolate reductase thermolabile variant and oral clefts.

Folic acid can prevent neural tube defects; in some cases the mechanism is probably a correction of a metabolic defect caused by thermolabile methylenetetrahydrofolate reductase (MTHFR) found in increased frequency in cases. It is less clear whether folic acid can prevent oral clefts, in part because it is not known whether thermolabile MTHFR is more common in those with oral clefts. This study examined the prevalence of the mutation (677 C-->T) that causes thermolabile MTHFR in subjects with oral clefts from a national Irish support group, and an anonymous control group randomly selected from a neonatal screening program covering all births in Ireland. Eighty-three of 848 control subjects were homozygous (TT) thermolabile MTHFR (9.8%). This defect was almost three times as common in the 27 subjects (25.9%) with isolated cleft palate (odds ratio 3.23, 95% confidence interval 1.32 -7.86, P = 0. 02) and somewhat more common in the 66 subjects with cleft lip with or without cleft palate (15.2%, odds ratio 1.65, 95% confidence interval 0.81-3.35, P = 0.20). When the two groups with different etiologies were combined, the overall odds ratio was 2.06 (95% confidence interval 1.16-3.66, P = 0.02). In the Irish population homozygosity for the common folate-related polymorphism associated with thermolabile MTHFR is significantly more frequent in those with isolated cleft palate, and could be etiologically important. Am. J. Med. Genet. 86:71-74, 1999. Published 1999 Wiley-Liss, Inc.

Evaluation of two new methods for routine measurement of alkaline phosphatase isoenzymes.

AIMS: To evaluate the performance of two new methods for the analysis of alkaline phosphatase (ALP) isoenzymes designed for use in the routine chemical pathology laboratory: pre-incubation with neuraminidase before agarose electrophoresis; and selective precipitation of the bone isoenzyme with wheat germ agglutinin (WGA). METHODS: Serum samples from 39 patients were analysed. Seventeen were from patients with liver disease, eight from patients with bone disease, and 14 from patients with normal ALP activity and no evidence of liver or bone disease. The two new methods were compared with the established method, wheat germ agglutinin affinity electrophoresis. RESULTS: There was good correlation between the neuraminidase and WGA electrophoretic methods. The WGA precipitation method showed negative interference in the measurement of bone isoenzyme activity in samples containing biliary alkaline phosphatase. Both the new methods had advantages of speed and simplicity over the existing method, but cost per test was considerably higher. CONCLUSIONS: The neuraminidase electrophoretic method is a satisfactory alternative to the WGA affinity electrophoretic method, although it is more expensive. The WGA precipitation method cannot be recommended for use with serum samples from patients with suspected liver disease.

Comparison of an immunochemical assay for plasma fibrinogen and a turbidimetric thrombin clotting technique to discriminate hyperlipidaemic patients from healthy controls.

Plasma samples from patients attending a lipid clinic (n = 14) and healthy control subjects (n = 21) were assayed for fibrinogen using an immunochemical method (radial immunodiffusion) and a turbidimetric assay based on the thrombin clotting technique. The patients had significantly higher plasma fibrinogen concentrations than controls by both methods, but there was significant overlap between the two groups when fibrinogen was assayed by the thrombin clotting technique; there was almost complete separation of the two groups using the immunochemical assay. This difference in overlap could not be attributed to the presence or absence of fibrinogen degradation products. These findings may have important implications for the choice of method for determining plasma fibrinogen when assays are used for the assessment of cardiovascular risk. It is recommended that plasma fibrinogen should be assayed by both an immuno-chemical and a thrombin clotting method.

Identification of bone and liver metastases from breast cancer by measurement of plasma alkaline phosphatase isoenzyme activity.

Plasma alkaline phosphatase isoenzyme activities were determined in patients with breast cancer to diagnose and monitor bone and liver metastases. Bone alkaline phosphatase activity was increased in 21 of 50 patients (42%) with radiologically confirmed bone metastases, while total alkaline phosphatase activity was increased in only 10 of 50 (20%); liver alkaline phosphatase activity was raised in 12 of 25 patients (48%) with liver metastases. All patients with liver metastases had bone metastases. Bone alkaline phosphatase activity was significantly higher in patients with symptomatic bone disease. Isoenzyme determination provided additional information that would have changed patient management in five of 20 patients who were monitored serially. Measurement of alkaline phosphatase isoenzyme activity, though less sensitive than imaging procedures, can assist in screening for, and in early detection of, a high proportion of bone and liver metastases, and can provide useful objective evidence of their response to treatment.

Plasma intestinal alkaline phosphatase and intermediate molecular mass gamma glutamyltransferase activities in the differential diagnosis of jaundice.

An assessment was made of the value of: (i) the demonstration of intestinal alkaline phosphatase in plasma for the differentiation of intrahepatic from post-hepatic jaundice in 122 jaundiced patients; and (ii) the demonstration of an intermediate molecular mass gamma glutamyltransferase in plasma for the identification of post-hepatic cholestasis in 74 jaundiced patients. The first test had a diagnostic sensitivity of only 32% with a specificity of 86%; the second test had a sensitivity of 50% and specificity of 75%. It is concluded that neither procedure is worth while.

Heat treatment for endocrinological investigations on plasma positive for human immunodeficiency virus (HIV).

The effects of heat treatment of serum samples on the hormone analyses used in this laboratory were studied. Total T4, testosterone, progesterone, and growth hormone were not systematically affected by heat treatment over the whole range of analyte concentrations studied; for thyroid stimulating hormone, no effect was noted on serum samples with concentrations of less than 10 mU/l. Significant changes occurred in total T3, cortisol, follicle stimulating hormone, luteinizing hormone, and prolactin. It is suggested that with appropriate preliminary study, heat treated plasma samples may be used in endocrinological investigations without adversely affecting the diagnostic validity of the results.

Development of a radioimmunoassay for measuring gonadotrophin releasing hormone in patients receiving treatment.

A radioimmunoassay for the measurement of gonadotrophin releasing hormone (GnRH) in plasma and urine using readily available reagents was developed. The GnRH assay showed good precision, recovery, and parallelism over a wide range of GnRH concentrations with a sensitivity of 15 pg/ml. The assay was compared with a commercially available kit (Buhlmann Laboratories). Although the Buhlmann kit showed acceptable precision, recovery, sensitivity, and correlation with the developed GnRH assay for plasma samples, lack of parallelism of serially diluted plasma and urine samples was consistently observed, together with a poor correlation with the developed GnRH assay for urine, suggesting a matrix effect with the Buhlmann kit. The developed assay is suitable for measuring GnRH in samples obtained from patients receiving pulsatile infusions of GnRH. In contrast, the commercially available Buhlmann kit was unsuitable for measuring plasma GnRH as the kit had a top standard of only 160 pg/ml, well below the peak plasma concentration. It would not be possible to dilute samples for analysis because of the lack of parallelism of diluted samples compared with standards obtained with the Buhlmann assay.

Measurement of biliary alkaline phosphatase by mini-column chromatography and by electrophoresis and its application to the detection of liver metastases in patients with breast cancer.

We describe a simple, rapid, and reproducible ion exchange mini-column chromatographic method for the quantitative measurement of biliary alkaline phosphatase in plasma. We have used this method to evaluate a cellulose acetate electrophoretic method, which was used to assess the value of measuring biliary alkaline phosphatase in 85 patients with breast cancer investigated for possible hepatic metastases. Biliary alkaline phosphatase activity was abnormal in 19 of 24 patients (79%) with liver metastases, but abnormalities were also found in 12 of 61 patients (20%) without hepatic metastases; in only 37% of patients with positive test results was this a consequence of liver metastases. For the identification of liver metastases, therefore, the method has useful sensitivity but limited specificity. Neither sensitivity nor specificity was significantly better than that of plasma gamma-glutamyltransferase activity, which was measured concomitantly.

Plasma ionised calcium in preterm infants: comparison with adults.

Plasma calcium (ionised and total) and albumin concentrations and pH were measured in preterm infants and in healthy adults and patients dependent on respirators. Plasma ionised calcium and total calcium values fell during the first week after birth and subsequently rose. Plasma ionised calcium concentrations in preterm infants were higher than those found in both healthy and sick adults. This difference was only partially explained by the lower blood pH in the infant population. There was no correlation between plasma ionised calcium or the ratio of ionised calcium to total calcium and total bilirubin concentrations. These results suggest that the metabolic control of plasma ionised calcium in preterm infants is different from that in adults.