Sufin Yap

Homocystinuria due to cystathionine β-synthase deficiency in Ireland: 25 years' experience of a newborn screened and treated population with reference to clinical outcome and biochemical control

Homocystinuria (HCU) due to cystathionine β-synthase deficiency (Mudd et al 1964) was independently described by Gerritsen and colleagues (USA) and Carson and colleagues (Northern Ireland) in 1962. The worldwide frequency of HCU has been reported as 1 in 344 000, while that in Ireland is much higher at 1 in 65 000, based on newborn screening and cases detected clinically. The national newborn screening programme for HCU in Ireland was started in 1971 using the bacterial inhibition assay. A total of 1.58 million newborn infants have been screened over a 25-year period up to 1996. Twenty-five HCU cases were diagnosed, 21 of whom were identified on screening. The remaining four HCU cases were missed and presented clinically; three of these were breast-fed and one was pyridoxine responsive. Twenty-four HCU cases were pyridoxine nonresponsive. Once the status of pyridoxine responsiveness was identified, all pyridoxine nonresponsive cases, but one, were started on a low methionine, cystine-enhanced diet supplemented with pyridoxine, vitamin B12 and folate. Dietary treatment commenced within 6 weeks of birth (range 8–42 days) for those cases detected by screening, while for the late-detected cases treatment was started upon presentation and diagnosis. Biochemical control was monitored measuring deproteinized plasma methionine, free homocystine and cystine at least once a month. Review of the clinical outcome of the 25 HCU cases with 365.7 patient-years of treatment revealed no HCU-related complications in 18 screened, dietary-treated cases. Fifteen of these had lifetime medians of free homocystine ≤11 μmol/L (range 4–11). The remaining three cases with higher lifetime medians of free homocystine (18, 18 and 48 μmol/L) have developed increasing myopia recently. Among the three screened non-dietary-compliant cases, two have ectopia lentis, one has osteoporosis and two have mental handicap. Of the four cases missed on screening, three presented with ectopia lentis after the age of 2 years. There were no thromboembolic events in any of the 25 HCU cases. The lifetime medians for methionine ranged from 47 to 134 μmol/L. The Irish HCU clinical outcome data suggest that newborn screening, early commencement of dietary treatment and a lifetime median of free homocystine of ≤11 μmol/L had significantly reduced the probability of developing complications when it was compared to the untreated HCU data (Mudd et al 1985).

Newborn screening for homocystinuria: Irish and world experience

Abstract Newborn screening for cystathionine β-synthase deficiency (homocystinuria; HCU) was started in the late 1960 s using a bacterial inhibition assay (BIA). At least seven countries have either national or regional screening programmes; 12 programmes are known to have discontinued. The worldwide incidence of HCU is approximately 1 in 335,000 but varies from 1 : 65,000 (Ireland) to 1 : 900,000 (Japan). Methodologies include the BIA, one-dimensional or thin-layer amino acid chromatography and, more recently, tandem mass spectrometry. The BIA diagnostic cut off concentration of blood methionine varies from 67 to 270 μmol/l (10–40 mg/l) with a median of 135 μmol/l (20 mg/l). In Ireland, 25 cases of HCU from 19 families have been identified from 1.58 million newborn infants since 1971; 21 cases were detected through the screening programme. Of the four missed cases, three were breast-fed at the time of blood collection and one was pyridoxine responsive. These findings were in broad agreement with the results from five other programmes, in which approximately one in every five cases was missed by the screening programme. Early hospital discharge, low protein intake, high blood methionine cut-off concentration and pyridoxine responsiveness were all identified as contributing to missed cases.

The intellectual abilities of early-treated individuals with pyridoxine-nonresponsive homocystinuria due to cystathionine β-synthase deficiency

The pathological sequelae of untreated homocystinuria due to cystathionine β-synthase deficiency include ectopia lentis, osteoporosis, thromboembolic events and mental retardation. They occur at a significantly higher rate with poorer mental capabilities (mean IQ = 57) in the untreated pyridoxine-nonresponsive individuals. The mental capabilities of 23 pyridoxine-nonresponsive individuals with 339 patient-years of treatment were assessed using age-appropriate psychometric tests and were compared to those of 10 unaffected siblings (controls). Of the 23 individuals, 19 were diagnosed through newborn screening with early treatment, two were late-detected and two were untreated at the time of assessment. Thirteen of the newborn, screened group who were compliant with treatment had no complications, while the remaining 6, who had poor compliance, developed complications. Good compliance was defined by a lifetime plasma free homocystine median < 11 μmol/L. The newborn screened, good compliance group (n = 13) with a mean age of 14.4 years (range 4.4–24.9) had mean full-scale IQ (FIQ) of 105.8 (range 84–120), while the poorly compliant group (n = 6) with a mean age of 19.9 years (range 13.8–25.5) had a mean FIQ of 80.8 (range 40–103). The control group (n = 10) with mean age of 19.4 years (range 9.7–32.9) years had a mean FIQ of 102 (range 76–116). The two late-detected patients aged 18.9 and 18.8 years had FIQ of 80 and 102, while the two untreated patients aged 22.4 and 11.7 years had FIQ of 52 and 53, respectively. There was no statistical evidence of significant differences between the compliant, early-treated individuals and their unaffected siblings (controls) except for the FIQ, which was significantly higher than that of the unaffected siblings (p = 0.0397). These data, despite the relatively small numbers, suggest that early treatment with good biochemical control (lifetime plasma free homocystine median < 11 μmol/L) seems to prevent mental retardation.

Management and investigation of neonatal encephalopathy: 2017 update

This review discusses an approach to determining the cause of neonatal encephalopathy, as well as current evidence on resuscitation and subsequent management of hypoxic-ischaemic encephalopathy (HIE). Encephalopathy in neonates can be due to varied aetiologies in addition to hypoxic-ischaemia. A combination of careful history, examination and the judicious use of investigations can help determine the cause. Over the last 7 years, infants with moderate to severe HIE have benefited from the introduction of routine therapeutic hypothermia; the number needed to treat for an additional beneficial outcome is 7 (95% CI 5 to 10). More recent research has focused on optimal resuscitation practices for babies with cardiorespiratory depression, such as delayed cord clamping after establishment of ventilation and resuscitation in air. Around a quarter of infants with asystole at 10 min after birth who are subsequently cooled have normal outcomes, suggesting that individualised decision making on stopping resuscitation is needed, based on access to intensive treatment unit and early cooling. The full benefit of cooling appears to have been exploited in our current treatment protocols of 72 hours at 33.5°C; deeper and longer cooling showed adverse outcome. The challenge over the next 5–10 years will be to assess which adjunct therapies are safe and optimise hypothermic brain protection in phase I and phase II trials. Optimal care may require tailoring treatments according to gender, genetic risk, injury severity and inflammatory status.

Diversity of cystathionine β‐synthase haplotypes bearing the most common homocystinuria mutation c.833T>C: a possible role for gene conversion

Homozygosity or compound heterozygosity for the c.833T>C transition (p.I278 T) in the cystathionine beta‐synthase (CBS) gene represents the most common cause of pyridoxine‐responsive homocystinuria in Western Eurasians. However, the frequency of the pathogenic c.833C allele, as observed in healthy newborns from several European countries (qc.833C ≊ 3.3 × 10–3), is ∼20‐fold higher than expected on the basis of the observed number of symptomatic homocystinuria patients carrying this mutation (qc.833C ≊ 0.18 × 10–3), implying clinical underascertainment. Intriguingly, the c.833C mutation is also present in combination with a 68‐bp insertion, c.[833C; 844_845ins68], in a substantial proportion of chromosomes from nonhomocystinuric individuals worldwide. We have sought to study the relationship between the pathogenic and nonpathogenic c.833C‐bearing chromosomes and to determine whether the pathogenic c.[833C; −] chromosomes are identical‐by‐descent or instead arose by recurrent mutation. Initial haplotype analysis of 780 randomly selected Czech and sub‐Saharan African wild‐type chromosomes, employing 12 intragenic markers, revealed 29 distinct CBS haplotypes, of which 10 carried the c.[833C; 844_845ins68] combination; none carried an isolated c.833C or c.844_845ins68 mutation. Subsequent examination of 69 pathogenic c.[833C; −] chromosomes, derived from homocystinuria patients of predominantly European origin, disclosed three unrelated haplotypes that differed from their wild‐type counterparts by virtue of the presence of c.833C, thereby indicating that c.833T>C transition has occurred repeatedly and independently in the past. Since c.833T does not reside within an obvious mutational hotspot, we surmise that the three pathogenic and comparatively prevalent c.[833C; −] chromosomes may have originated by recurrent gene conversion employing the common nonpathogenic c.[833C; 844_845ins68] chromosomes as templates. Hum Mutat 28(3), 255–264, 2007. Published 2006 Wiley‐Liss, Inc.

New insights into the genetics of 5-oxoprolinase deficiency and further evidence that it is a benign biochemical condition

AbstractInherited 5-oxoprolinase (OPLAH) deficiency is a rare inborn condition characterised by 5-oxoprolinuria. To date, three OPLAH mutations have been described: p.H870Pfs in a homozygous state, which results in a truncated protein, was reported in two siblings, and two heterozygous missense changes, p.S323R and p.V1089I, were independently identified in two unrelated patients. We describe the clinical context of a young girl who manifested 5-oxoprolinuria together with dusky episodes and who is compound heterozygote for two novel OPLAH variations: p.G860R and p.D1241V. To gain insight into the aetiology of the 5-oxoprolinase deficiency, we investigated the pathogenicity of all the reported missense mutations in the OPLAH gene. A yeast in vivo growth assay revealed that only p.S323R, p.G860R and p.D1241V affected the activity of the enzyme. Conclusion: Taken together, this report further suggests that hereditary 5-oxoprolinase deficiency is a benign biochemical condition caused by mutations in the OPLAH gene, which are transmitted in an autosomal recessive manner, but 5-oxoprolinuria may be a chance association in other disorders.

N-Carbamylglutamate Is an Effective Treatment for Acute Neonatal Hyperammonaemia in a Patient with Methylmalonic Aciduria

N-carbamylglutamate (NCG) has been used in combination with ammonia scavengers (sodium benzoate, sodium phenylbutyrate) and dialysis to treat hyperammonaemia in methylmalonic aciduria (MMA). The sole use of NCG for acute neonatal hyperammonaemia secondary to MMA is demonstrated in a neonate presenting at day 9 with encephalopathy, severe metabolic acidosis, hyperammonaemia (1,089 μmol/l), ketonuria and urinary methylmalonic acids. Emergency treatment included discontinuing protein feeds, providing high calories, carnitine and hydroxocobalamin. NCG 200 mg given at 0 and 90 min decreased plasma ammonia dramatically from 1,089 to 567 µmol/l at 90 min and further to 236 µmol/l at 6 h. Normalisation of ammonia was achieved at 12 h with two further doses of NCG 100 mg. This allowed for early re-institution of feeds at 14 h, followed by metabolic stabilization and recovery. Due to the effectiveness of NCG in this case, the use of the more invasive conventional ammonia-lowering therapeutic options could be avoided.

Succinic Semialdehyde Dehydrogenase Deficiency in a Chinese Boy A Novel ALDH5A1 Mutation With Severe Phenotype

Succinic semialdehyde dehydrogenase deficiency is a rare autosomal recessive disorder affecting catabolism of the neurotransmitter gamma-aminobutyric acid (GABA), with a wide range of clinical phenotype. We report a Malaysian Chinese boy with a severe early onset phenotype due to a previously unreported mutation. Urine organic acid chromatogram revealed elevated 4-hydroxybutyric acid. Magnetic resonance imaging (MRI) of the brain demonstrated cerebral atrophy with atypical putaminal involvement. Molecular genetic analysis showed a novel homozygous 3-bp deletion at the ALDH5A1 gene c.1501_1503del (p.Glu501del). Both parents were confirmed to be heterozygotes for the p.Glu501del mutation. The clinical course was complicated by the development of subdural hemorrhage probably as a result of rocking the child to sleep for erratic sleep-wake cycles. This case illustrates the need to recognize that trivial or unintentional shaking of such children, especially in the presence of cerebral atrophy, can lead to subdural hemorrhage.

The Treatment of High Homocysteine Concentrations in Homocystinuria: Biochemical Control in Patients and Their Vascular Outcome

The natural history of individuals with homocystinuria due to cystathionine β-synthase deficiency was first documented in 1985 by Mudd et al [1]. Untreated, these individuals have severe hyperhomocysteinemia resulting in complications involving the eye (ectopia lentis), skeletal (osteoporosis, dolichostenomelia), vascular (thromboembolic events) and central nervous systems. Vascular complications are, however, the most striking cause of major morbidity and mortality in homocystinuric individuals. The aims of treatment must be to prevent or ameliorate particularly these life-endangering events by controlling or eliminating the severe hyperhomocysteinemia. There are currently three recognized modalities of treatment. For the pyridoxine responsive individual, pyridoxine in pharmacological doses in combination with folic acid and vitamin B12 will correct the biochemical abnormalities. In pyridoxine-nonresponsive homocystinuria, a methionine restricted, cystine supplemented diet in combination with the use of pyridoxine, folic acid and vitamin B12 is the treatment. However, good compliance with the diet may be difficult to obtain particularly in the late-detected individuals. Betaine, a methyl donor, may be useful in these individuals or as an adjunct to such a diet. Additional medical measures that do not affect the biochemical abnormalities but aim at reducing or eliminating the thrombotic tendencies have also been used. These include dipyridamole, either alone or in combination with aspirin to normalise decreased platelet survival and minimise vascular intimal lesions, the avoidance of situations associated with an increased risk of thromboembolism and the use of high dose antithrombotic prophylaxis with heparin or warfarin in conditions with prolonged bedrest. From the data recently published by the centers treating a total of 84 homocystinuric individuals with 1314 patient-years of treatment in Australia [4], the Netherlands [5] and Ireland [6], 53 vascular events would have been expected if they had remained untreated according to the data of Mudd et al[1]. Instead only five have been recorded while on treatment (relative risk = 0.091 (95% CI 0.043–0.190); p<0.001). This clearly establishes that appropriate treatment of severe hyperhomocysteinemia significantly reduces the vascular risk in homocystinuria, albeit post-treatment homocysteine levels may still be several times higher than the cut-off point for homocysteine in the normal population. The present findings may have relevance to the current concept of mild hyperhomocysteinemia and its association with cardiovascular disease, in which the elevation of plasma homocysteine levels is considerably lower than the post-treatment levels reported by the three centers.

Transient 5-oxoprolinuria: unusually high anion gap acidosis in an infant

AbstractTransient 5-oxoprolinuria is a phenomenon that is well recognised in adults. We illustrate an unusual paediatric case of transient 5-oxoprolinuria presenting during an episode of severe sepsis with concomitant paracetamol use. The 15-month-old patient had an extremely high anion gap metabolic acidosis. Adequate resuscitation failed to correct the biochemical disturbance, and high levels of 5-oxoproline were identified. A combination of haemofiltration, replenishment of glutathione stores with N-acetylcysteine and cessation of paracetamol administration resulted in the resolution of the acidosis. Subsequent testing following treatment of the sepsis revealed no ongoing 5-oxoprolinuria. Conclusion: Transient 5-oxoprolinuria has been previously reported in the adult population during episodes of severe sepsis and various pharmaceutical interventions. This case illustrates that it is a phenomenon that should be considered in paediatric patients where a very high anion gap metabolic acidosis exists that cannot be explained by the biochemical indices.What is Known:• 5-oxoprolinuria in the paediatric population is usually secondary to an inborn error of metabolism.• Transient 5-oxoprolinuria is well recognised in adults during episodes of severe glutathione depletion.What is New:• Transient 5-oxoprolinuria is a phenomenon rarely reported in the paediatric population.• It highlights the importance of investigating a high anion gap such that unusual diagnoses are not missed.