Total plasma homocysteine measurement: Evaluation of the Abbott immunoassay, comparison with the JEOL ion exchange chromatography and investigation of its clinical utility.

Objectives: Homocysteine is an intermediary amino acid formed in methionine metabolism, with elevated total homocysteine (tHCY) being a biomarker of cardiovascular and cerebrovascular diseases. We evaluated the Abbott ARCHITECT tHCY immunoassay, compared it with the current established JEOL ion exchange chromatography (IEC) method and evaluated its clinical utility. Design and methods: Following immunoassay method verification, plasma samples of 91 patients were analysed for tHCY using immunoassay and IEC. Results: For the Abbott immunoassay, accuracy was assessed, with UK NEQAS EQA specimens, by the correlation of our Abbott immunoassay measurements to the Abbott ARCHITECT immunoassay mean (bias = 1.6%), and to the overall immunoassay mean (bias = 2.0%). The total imprecision was 2.7% (11.00 µmol/L), 2.4% (16.80 µmol/L) and 2.8% (24.30 µmol/L) respectively. Bias in linearity assessment was 0.12%-2.58%. The inter-method correlation was strong in Passing-Bablok regression: immunoassay = IEC x0.857 + 2.445 (95% CI: slope = [0.742,0.947], intercept = [1.340,3.582]), with Spearman correlation = 0.803 (p < 0.001). The Bland-Altman plot showed an average difference of -0.284 µmol/L (95% CI: [-1.043,0.474]) with limits of agreement (mean ± 1.96SD) from -7.425 µmol/L to 6.857 µmol/L.No significant difference in tHCY was found using both methods in patients with cerebrovascular diseases and cardiovascular diseases. Most tHCY measurements were within the reference ranges of both methods. All homocystinuria patients had tHCY values above the reference ranges of both methods. Conclusions: The immunoassay demonstrated robust performance in its verification and showed good comparability with the IEC but with some biases so caution is needed if both are used interchangeably. The immunoassay offers an automated alternative to IEC in the assessment of hyperhomocysteinaemia.

Sweat testing in the modern era: A national survey of sweat testing practice in the Republic of Ireland.

BACKGROUND: The sweat test has been the "gold standard" diagnostic test for cystic fibrosis for more than 40 years. We hypothesized that there would be a change in the pattern of sweat testing in Ireland since the introduction of cystic fibrosis newborn screening in 2011, when practices were last reviewed. This is a follow up survey looking at sweat testing numbers and practices. METHODS: A national survey compiled data on sweat collection, conductivity and sweat chloride testing in all hospitals previously identified as performing sweat tests. RESULTS: All 13 centres in Ireland performing sweat testing in 2018 responded to the survey (100% return rate). Our results indicate that 1007 sweat tests were performed in 2018 compared to 2555 in 2011, equating to a 61% reduction. Seven out of 13 centres are performing less than 50 sweat tests per year. Nine out of 13 centres (69%) had a sweat test failure rate greater than the recommended allowable rate of ≤ 10%. We detected a trend of sweat testing in patients with an existing diagnosis of CF who had commenced cystic fibrosis transmembrane conductance regulator (CFTR) modulators. CONCLUSIONS: There has been a significant reduction in the number of sweat tests performed in Ireland since the introduction of newborn screening for CF. There remains a lack of standardisation in many aspects of the service ranging from sample collection to reporting of results. We have identified a new trend of sweat testing in the cystic fibrosis transmembrane conductance regulator modulator era.

Hypophosphatasia.

Hypophosphatasia (HPP) is a group of inherited disorders characterised by the impaired mineralisation of bones and/or teeth and low serum alkaline phosphatase (ALP) activity. It is caused by a mutation in the ALPL gene encoding the tissue-non-specific isoenzyme of ALP (TNSALP) resulting in a loss of function. The disease is highly heterogenous in its clinical expression ranging from stillbirth without mineralised bone to the mild form of late adult onset with symptoms and signs such as musculoskeletal pain, arthropathy, lower-extremity fractures, premature loss of teeth or an incidental finding of reduced serum ALP activity. A classification based on the age at diagnosis and the presence or absence of bone symptoms was historically used: perinatal, prenatal benign, infantile, childhood, adult and odontohypophosphatasia. These subtypes are known to have overlapping signs and complications. Three forms of HPP distinguishable by their genetic characteristics have been described: severe, moderate and mild. Severe forms of HPP (perinatal and infantile severe) are recessively inherited, whereas moderate HPP may be dominantly or recessively inherited. The biochemical hallmark of HPP is persistently low serum ALP for age and increase in natural substrates of TNSALP, pyridoxal 5'-phosphate and phosphoethanolamine supported by radiological findings. The diagnosis is confirmed by ALPL sequencing. A multidisciplinary team of experts is essential for the effective management. Calcium restriction is recommended in infants/children to manage hypercalcaemia. A targeted enzyme replacement therapy for HPP has become available and correct diagnosis is crucial to allow early treatment.

Maple syrup urine disease: Clinical outcomes, metabolic control, and genotypes in a screened population after four decades of newborn bloodspot screening in the Republic of Ireland.

Since 1972, 18 patients (10 females/8 males) have been detected by newborn bloodspot screening (NBS) with neonatal-onset maple syrup urine disease (MSUD) in Ireland. Patients were stratified into three clusters according to clinical outcome at the time of data collection, including developmental, clinical, and IQ data. A fourth cluster comprised of two early childhood deaths; a third patient died as an adult. We present neuroimaging and electroencephalography together with clinical and biochemical data. Incidence of MSUD (1972-2018) was 1 in 147 975. Overall good clinical outcomes were achieved with 15/18 patients alive and with essentially normal functioning (with only the lowest performing cluster lying beyond a single SD on their full scale intelligence quotient). Molecular genetic analysis revealed genotypes hitherto not reported, including a possible digenic inheritance state for the BCKDHA and DBT genes in one family. Treatment has been based on early implementation of emergency treatment, diet, close monitoring, and even dialysis in the setting of acute metabolic decompensation. A plasma leucine ≥400 µmol/L (outside therapeutic range) was more frequently observed in infancy or during adolescence, possibly due to infections, hormonal changes, or noncompliance. Children require careful management during metabolic decompensations in early childhood, and this represented a key risk period in our cohort. A high level of metabolic control can be achieved through diet with early implementation of a "sick day" regime and, in some cases, dialysis as a rescue therapy. The Irish cohort, despite largely classical phenotypes, achieved good outcomes in the NBS era, underlining the importance of early diagnosis and skilled multidisciplinary team management.

Hypoglycemia is not a defining feature of metabolic crisis in mitochondrial 3-hydroxy-3-methylglutaryl-CoA synthase deficiency: Further evidence of specific biochemical markers which may aid diagnosis.

Mitochondrial 3-hydroxy-3-methylglutaryl-CoA (HMG Co-A) synthase (mHS) deficiency is an autosomal recessive disorder of ketone body synthesis which has traditionally been associated with hypoketotic hypoglycemia, hepatomegaly and encephalopathy, presenting in early childhood following a period of fasting. We report the third case of mHS deficiency presenting in the absence of hypoglycemia, with profound biochemical abnormalities and further evidence of potential specific diagnostic biomarkers. A previously well, 20-month old, unvaccinated male, of nonconsanguineous Polish heritage, presented with encephalopathy, hepatomegaly, severe metabolic acidosis, and mild hyperammonemia following a brief intercurrent illness. The patient was reported to have taken colloidal silver prior to presentation, posing a further diagnostic challenge. Additionally, he developed features suggestive of hemophagocytic lymphohistiocytosis during treatment. While the patient was normoglycemic prior to dextrose administration, the sample was markedly lipemic, with significant hypertriglyceridemia detected. Urine organic acid analysis revealed dicarboxylic aciduria with 4-hydroxy-6-methyl-2-pyrone (4HMP) and the presence of three other previously reported putative biomarkers for mHS deficiency. Glutarate was markedly elevated in the initial chromatogram, with a mild increase in 3-hydroxyglutarate (3HG) persisting. Raised acetylcarnitine was detected on acylcarnitine profile. Molecular genetic analysis of the HMGCS2 gene identified compound heterozygosity for known pathogenic mutations c.634G>A and c.1016+1G>A, confirming the diagnosis of mHS deficiency. This case provides further evidence that hypoglycemia is not invariably present in symptomatic mHS deficiency. We propose that elevated acetylcarnitine, triglycerides, and 3HG are additional biochemical features during acute presentations. With the expansion of novel biomarkers, further cases of this rare disorder may emerge.

National Newborn Screening for cystic fibrosis in the Republic of Ireland: genetic data from the first 6.5 years.

Cystic fibrosis (CF) is the most common life-limiting autosomal recessive disease in the Republic of Ireland (ROI), with a previously quoted incidence of 1 in 1353 and carrier rate of 1 in 19. The National Newborn Screening (NBS) for CF was incorporated in July 2011 in the ROI. A cut-off point of the top 1% Immunoreactive Trypsinogen (IRT) was taken as an indication for 38 CFTR variant panel to maximise identification of affected CF cases and to minimise detection of carriers. All neonates from July 2011 to Dec 2017 with an elevated IRT on NBS were tested with 38 CFTR mutation panel and included. Clinical and laboratory database were analysed. In the first 6.5 years a total of 5,053 newborns (1.16% of total births) were screened with 38 CFTR panel. 170 CF affected cases, 320 unaffected carriers, 32 CF Screening Positive Inconclusive Diagnosis (CFSPID) were identified. There was one missed diagnosis. The most common disease-causing variant was c.1521_1523delCTT (p.(Phe508del)) followed by c.1652G>A (p.(Gly551Asp)). 95 out of 170 (55%) affected newborns were homozygous for c.1521_1523delCTT (p.(Phe08del)) and 25 (15%) carried at least one copy of c.1652G>A (p.(Gly551Asp)). Hence, 70% of affected newborns were eligible for CFTR modulator treatment. The NBS programme has identified almost triple the number of affected newborn with c.1652G>A (p.(Gly551Asp)) than previously quoted figures and identified less than 50% of carriers than predicted. The revised incidence and carrier frequency of CF in the ROI is 1 in 2570 and 1 in 25, respectively.

Two Uneventful Pregnancies in a Woman with Glutaric Aciduria Type 1.

Glutaric aciduria type 1 (GA1) is an autosomal recessive rare disorder caused by mutations in the GCDH gene resulting in deficiency of glutaryl-CoA dehydrogenase, leading to accumulation of the amino acids lysine, hydroxylysine and tryptophan and other metabolites. The phenotypic spectrum of disease is broad. Stress caused by infection and fever and possibly pregnancy may lead to worsening of the signs and symptoms, often with uncertain recovery.We describe a case of a female patient with GA1 who had two clinically uneventful pregnancies.At the age of 11 she was diagnosed with GA1 by family screening. The cultured skin fibroblast showed reduced glutaryl-CoA dehydrogenase activity (0.16 mg protein per min).The initial diagnostic urine glutaric acid level for this patient was 1,784 µmol/mmol creatinine. Mutation analysis showed compound heterozygosity for the p.(Gly185Arg), c.553G>A in exon 7 and p.(Arg402Trp), c.1204C.T in exon 11 mutations of the GCDH.Her pregnancy at the age of 23 was complicated by pre-eclampsia and required treatment with beta-blockers. Four years later the second pregnancy was uncomplicated. The management plan during the caesarean section included intravenous dextrose and lipid infusions. The patient rapidly recovered from both surgeries.Both babies have had normal development to date. On newborn screening, plasma acylcarnitine showed a transient increase in glutarylcarnitine, and the urine organic acid analysis showed a trace of 3-hydroxyglutarylcarnitine, likely to be of maternal transfer.The multidisciplinary team, consisting of metabolic, dietetic and obstetric care providers, have responsibility to ensure the risk of acute decompensation in pregnant GA1 women is minimal.

Fault lines in forensic medical toxicology in Ireland exposed through replies of pathologists and coroners to anonymous questionnaires.

The attitudes and experiences of pathologists and coroners to the provision of biochemical forensic toxicology in the Republic of Ireland were determined using separate questionnaires to each group anonymously. Replies were received from 36/88 (41%) of pathologists and 19/71 (27%) of coroners. 37% of coroners considered that histopathologists give an adequate opinion in forensic toxicology yet 58% of pathologists reported that they did not have adequate access to expert medical interpretative toxicological opinion. For drug-drug interactions and metabolic diseases, 69% of pathologists were unhappy with the processes and 68% of coroner replies did not know if vitreous samples were used appropriately. There is a clear requirement for retraining of coroners and for the appointment of medical toxicology expertise to improve the quality of service for coroners.