Joy Yaplito-Lee

Successful treatment of molybdenum cofactor deficiency type A with cPMP

Molybdenum cofactor deficiency (MoCD) is a rare metabolic disorder characterized by severe and rapidly progressive neurologic damage caused by the functional loss of sulfite oxidase, 1 of 4 molybdenum-dependent enzymes. To date, no effective therapy is available for MoCD, and death in early infancy has been the usual outcome. We report here the case of a patient who was diagnosed with MoCD at the age of 6 days. Substitution therapy with purified cyclic pyranopterin monophosphate (cPMP) was started on day 36 by daily intravenous administration of 80 to 160 μg of cPMP/kg of body weight. Within 1 to 2 weeks, all urinary markers of sulfite oxidase (sulfite, S-sulfocysteine, thiosulfate) and xanthine oxidase deficiency (xanthine, uric acid) returned to almost normal readings and stayed constant (>450 days of treatment). Clinically, the infant became more alert, convulsions and twitching disappeared within the first 2 weeks, and an electroencephalogram showed the return of rhythmic elements and markedly reduced epileptiform discharges. Substitution of cPMP represents the first causative therapy available for patients with MoCD. We demonstrate efficient uptake of cPMP and restoration of molybdenum cofactor–dependent enzyme activities. Further neurodegeneration by toxic metabolites was stopped in the reported patient. We also demonstrated the feasibility to detect MoCD in newborn-screening cards to enable early diagnosis.

Expanded newborn screening: Outcome in screened and unscreened patients at age 6 years

OBJECTIVE: Tandem mass spectrometry is widely applied to routine newborn screening but there are no long-term studies of outcome. We studied the clinical outcome at six years of age in Australia. METHODS: In a cohort study, we analyzed the outcome at 6 years for patients detected by screening or by clinical diagnosis among >2 million infants born from 1994 to 1998 (1 017 800, all unscreened) and 1998 to 2002 (461 500 screened, 533 400 unscreened) recording intellectual and physical condition, school placement, other medical problems, growth, treatment, diet, and hospital admissions. Results were analyzed separately for medium-chain acyl-CoA dehydrogenase deficiency (MCADD) and other disorders, and grouped patients as those who presented clinically or died in the first 5 days of life; patients presented later or diagnosed by screening, and those with substantially benign disorders. RESULTS: Inborn errors, excluding phenylketonuria, were diagnosed in 116 of 1 551 200 unscreened infants (7.5/100 000 births) and 70 of 461 500 screened infants (15.2/100 000 births). Excluding MCADD, 21 unscreened patients with metabolic disorders diagnosed after 5 days of life died or had a significant intellectual or physical handicap (1.35/100 000 population) compared with 2 of the screened cohort (0.43/100 000; odds ratio: 3.1 [95% CI: 0.73–13.32]). Considering the likely morbidity or mortality among the expected number of never-diagnosed unscreened patients, there would be a significant difference. Growth distribution was normal in all cohorts. CONCLUSION: Screening by tandem mass spectrometry provides a better outcome for patients at 6 years of age, with fewer deaths and fewer clinically significant disabilities.

A prospective evaluation of whole-exome sequencing as a first-tier molecular test in infants with suspected monogenic disorders.

Purpose:To prospectively evaluate the diagnostic and clinical utility of singleton whole-exome sequencing (WES) as a first-tier test in infants with suspected monogenic disease.Methods:Singleton WES was performed as a first-tier sequencing test in infants recruited from a single pediatric tertiary center. This occurred in parallel with standard investigations, including single- or multigene panel sequencing when clinically indicated. The diagnosis rate, clinical utility, and impact on management of singleton WES were evaluated.Results:Of 80 enrolled infants, 46 received a molecular genetic diagnosis through singleton WES (57.5%) compared with 11 (13.75%) who underwent standard investigations in the same patient group. Clinical management changed following exome diagnosis in 15 of 46 diagnosed participants (32.6%). Twelve relatives received a genetic diagnosis following cascade testing, and 28 couples were identified as being at high risk of recurrence in future pregnancies.Conclusions:This prospective study provides strong evidence for increased diagnostic and clinical utility of singleton WES as a first-tier sequencing test for infants with a suspected monogenic disorder. Singleton WES outperformed standard care in terms of diagnosis rate and the benefits of a diagnosis, namely, impact on management of the child and clarification of reproductive risks for the extended family in a timely manner.Genet Med 18 11, 1090–1096.

New indications and controversies in arginine therapy

Arginine is an important, versatile and a conditionally essential amino acid. Besides serving as a building block for tissue proteins, arginine plays a critical role in ammonia detoxification, and nitric oxide and creatine production. Arginine supplementation is an essential component for the treatment of urea cycle defects but recently some reservations have been raised with regards to the doses used in the treatment regimens of these disorders. In recent years, arginine supplementation or restriction has been proposed and trialled in several disorders, including vascular diseases and asthma, mitochondrial encephalopathy lactic acidosis and stroke-like episodes (MELAS), glutaric aciduria type I and disorders of creatine metabolism, both production and transportation into the central nervous system. Herein we present new therapeutic indications and controversies surrounding arginine supplementation or deprivation.

Mitochondrial Oxidative Phosphorylation Disorders Presenting in Neonates: Clinical Manifestations and Enzymatic and Molecular Diagnoses

OBJECTIVES. The goals were to examine the frequency of perinatal manifestations of mitochondrial oxidative phosphorylation disorders within a population-based cohort, to characterize these manifestations, to identify a possible association between these manifestations and diagnoses at a later age, and to identify possible associations between perinatal complications and specific disorders. METHODS. We conducted a retrospective review of clinical and laboratory records for all patients with definitive oxidative phosphorylation disorders who were diagnosed and treated at the Royal Childrens Hospital in Melbourne between 1975 and 2006 (N = 107; male/female ratio: 1.41). RESULTS. Neonatal presentation was recorded for 32 of 107 patients (male/female ratio: 1:1), including 19 who presented on day 1 of life. Prematurity (gestational age of <37 weeks) was noted for 12.6% of the 107 patients. Of the 85 infants with known birth weights, 24 were in the ≤10th percentile for gestational age (11 with complex I deficiency), and 9 of those (6 with complex I deficiency) were in the <3rd percentile. The most common presenting neonatal symptoms after the first day of life were poor feeding, recurrent vomiting, and failure to thrive. We noted 3 main clinical neonatal forms of oxidative phosphorylation disorders (encephalomyopathic, hepatointestinal, and cardiac). Of the 32 infants, 28 died (13 in the neonatal period). Complex I deficiency was identified for 15 neonates, combined complexes I, III, and IV deficiency for 7 neonates, and combined complexes I and IV deficiency for 3 neonates. No neonates had complex IV deficiency. Six neonates had nuclear mutations, and 2 neonates had the mitochondrial DNA 8993T>G mutation. CONCLUSIONS. Oxidative phosphorylation disorders present commonly in the neonatal period. The combination of nonspecific manifestations such as prematurity and intrauterine growth retardation with early postnatal decompensation or poor feeding or vomiting and persistent lactic acidosis should suggest the possibility of an oxidative phosphorylation disorder.

Phenotype and genotype in 101 males with X-linked creatine transporter deficiency

Background Creatine transporter deficiency is a monogenic cause of X-linked intellectual disability. Since its first description in 2001 several case reports have been published but an overview of phenotype, genotype and phenotype–genotype correlation has been lacking. Methods We performed a retrospective study of clinical, biochemical and molecular genetic data of 101 males with X-linked creatine transporter deficiency from 85 families with a pathogenic mutation in the creatine transporter gene (SLC6A8). Results and conclusions Most patients developed moderate to severe intellectual disability; mild intellectual disability was rare in adult patients. Speech language development was especially delayed but almost a third of the patients were able to speak in sentences. Besides behavioural problems and seizures, mild to moderate motor dysfunction, including extrapyramidal movement abnormalities, and gastrointestinal problems were frequent clinical features. Urinary creatine to creatinine ratio proved to be a reliable screening method besides MR spectroscopy, molecular genetic testing and creatine uptake studies, allowing definition of diagnostic guidelines. A third of patients had a de novo mutation in the SLC6A8 gene. Mothers with an affected son with a de novo mutation should be counselled about a recurrence risk in further pregnancies due to the possibility of low level somatic or germline mosaicism. Missense mutations with residual activity might be associated with a milder phenotype and large deletions extending beyond the 3′ end of the SLC6A8 gene with a more severe phenotype. Evaluation of the biochemical phenotype revealed unexpected high creatine levels in cerebrospinal fluid suggesting that the brain is able to synthesise creatine and that the cerebral creatine deficiency is caused by a defect in the reuptake of creatine within the neurones.

ECHS1 mutations in Leigh disease: a new inborn error of metabolism affecting valine metabolism

Two siblings with fatal Leigh disease had increased excretion of S-(2-carboxypropyl)cysteine and several other metabolites that are features of 3-hydroxyisobutyryl-CoA hydrolase (HIBCH) deficiency, a rare defect in the valine catabolic pathway associated with Leigh-like disease. However, this diagnosis was excluded by HIBCH sequencing and normal enzyme activity. In contrast to HIBCH deficiency, the excretion of 3-hydroxyisobutyryl-carnitine was normal in the children, suggesting deficiency of short-chain enoyl-CoA hydratase (ECHS1 gene). This mitochondrial enzyme is active in several metabolic pathways involving fatty acids and amino acids, including valine, and is immediately upstream of HIBCH in the valine pathway. Both children were compound heterozygous for a c.473C > A (p.A158D) missense mutation and a c.414+3G>C splicing mutation in ECHS1. ECHS1 activity was markedly decreased in cultured fibroblasts from both siblings, ECHS1 protein was undetectable by immunoblot analysis and transfection of patient cells with wild-type ECHS1 rescued ECHS1 activity. The highly reactive metabolites methacrylyl-CoA and acryloyl-CoA accumulate in deficiencies of both ECHS1 and HIBCH and are probably responsible for the brain pathology in both disorders. Deficiency of ECHS1 or HIBCH should be considered in children with Leigh disease. Urine metabolite testing can detect and distinguish between these two disorders.

Mitochondrial Carbonic Anhydrase VA Deficiency Resulting from CA5A Alterations Presents with Hyperammonemia in Early Childhood

Four children in three unrelated families (one consanguineous) presented with lethargy, hyperlactatemia, and hyperammonemia of unexplained origin during the neonatal period and early childhood. We identified and validated three different CA5A alterations, including a homozygous missense mutation (c.697T>C) in two siblings, a homozygous splice site mutation (c.555G>A) leading to skipping of exon 4, and a homozygous 4 kb deletion of exon 6. The deleterious nature of the homozygous mutation c.697T>C (p.Ser233Pro) was demonstrated by reduced enzymatic activity and increased temperature sensitivity. Carbonic anhydrase VA (CA-VA) was absent in liver in the child with the homozygous exon 6 deletion. The metabolite profiles in the affected individuals fit CA-VA deficiency, showing evidence of impaired provision of bicarbonate to the four enzymes that participate in key pathways in intermediary metabolism: carbamoylphosphate synthetase 1 (urea cycle), pyruvate carboxylase (anaplerosis, gluconeogenesis), propionyl-CoA carboxylase, and 3-methylcrotonyl-CoA carboxylase (branched chain amino acids catabolism). In the three children who were administered carglumic acid, hyperammonemia resolved. CA-VA deficiency should therefore be added to urea cycle defects, organic acidurias, and pyruvate carboxylase deficiency as a treatable condition in the differential diagnosis of hyperammonemia in the neonate and young child.

Newborn screening for glutaric aciduria type I in Victoria: treatment and outcome.

Between October 2001 and September 2007, a total number of 391,651 neonates were screened in Victoria using Tandem Mass Spectrometry and 6 newborns were diagnosed as having GA I, giving an incidence of 1:65,275 (CI: 1:29,988=1:177,861). Another patient was diagnosed through cascade screening of children born before the implementation of the expanded newborn screening program. Patients were treated by mild protein restriction (2-2.5 g/kg/day) and carnitine supplementation when well, focussing on the aggressive management of intercurrent illnesses (temporary cessation of protein intake, increase in calorie intake, IV carnitine, aggressive anti febrile and anti infectious treatment), including prophylactic admissions to hospital. Overall, our patients had 35 admissions to hospital, of which 15 were in the first year of life. None had a post infectious dystonic syndrome. Neuropsychological examinations revealed normal to high cognitive and gross motor function in all patients but one, with some deficiencies in fine motor activities and different levels of speech abnormalities in all patients. Since therapeutic approaches for GA I, although not uniform, are well established and have been documented to be effective, newborn screening for this disorder should prove justified. A therapeutic approach of dietary modification, IV carnitine and aggressive treatment of intercurrent illness seems to prevent the severe neurological complications of GA I. More in-depth consideration of speech and language function is necessary to document specific deficits in children with GA I and plan proactive interventions.

A retrospective audit of anesthetic techniques and complications in children with mucopolysaccharidoses

Objectives and aims: To document the incidence of difficult airway management and difficult intubation in the era of replacement therapy for Australian children with mucopolysaccharidosis (MPS).