Impact of citrulline substitution on clinical outcome after liver transplantation in carbamoyl phosphate synthetase 1 and ornithine transcarbamylase deficiency

Carbamoyl phosphate synthetase 1 (CPS1) and ornithine transcarbamylase (OTC) deficiencies are rare urea cycle disorders, which can lead to life-threatening hyperammonemia. Liver transplantation (LT) provides a cure and offers an alternative to medical treatment and life-long dietary restrictions with permanent impending risk of hyperammonemia. Nevertheless, in most patients, metabolic aberrations persist after LT, especially low plasma citrulline levels, with questionable clinical impact. So far, little is known about these alterations and there is no consensus, whether l-citrulline substitution after LT improves patients' symptoms and outcomes. In this multicentre, retrospective, observational study of 24 patients who underwent LT for CPS1 (n = 11) or OTC (n = 13) deficiency, 25% did not receive l-citrulline or arginine substitution. Correlation analysis revealed no correlation between substitution dosage and citrulline levels (CPS1, p = 0.8 and OTC, p = 1). Arginine levels after liver transplantation were normal after LT independent of citrulline substitution. Native liver survival had no impact on mental impairment (p = 0.67). Regression analysis showed no correlation between l-citrulline substitution and failure to thrive (p = 0.611) or neurological outcome (p = 0.701). Peak ammonia had a significant effect on mental impairment (p = 0.017). Peak plasma ammonia levels correlate with mental impairment after LT in CPS1 and OTC deficiency. Growth and intellectual impairment after LT are not significantly associated with l-citrulline substitution.

Fabry-specific treatment in Australia: time to align eligibility criteria with international best practices

BACKGROUND

Disease-specific therapy aims to improve symptoms, stabilise current disease and delay progression in patients with Fabry disease. In Australia, treatment access is subject to eligibility criteria initially established in 2004. Patients and their clinicians question why these criteria have remained unchanged despite significant progress in disease understanding.

AIMS

Appraise the clinical quality of the Australian treatment access criteria.

METHODS

The Fabry Australia Medical Advisory Committee (N = 6) used the Appraisal of Guidelines for REsearch and Evaluation Global Rating Scale (AGREE II GRS) to assess the clinical quality of the current treatment eligibility criteria. They reviewed the literature, developed 17 clinical statements to help guide reforms of the eligibility criteria and achieved consensus (achievement of ≥75% agreement in the range 5-7 on a 7-point Likert scale) through anonymous voting. The findings were applied to develop proposals for revised classification and treatment initiation criteria.

RESULTS

The current treatment eligibility criteria underperformed on the AGREE II GRS. They are pragmatic but out-of-step with contemporary data. Consensus was achieved on all 17 proposed clinical statements. There was strong agreement to differentiate classical male Fabry patients to facilitate timelier access to Fabry-specific treatment. There was also agreement on the value of adopting relevant organ involvement criteria in classical female patients and patients with non-classical disease.

CONCLUSIONS

Australian access criteria are misaligned with current clinical evidence. The clinical statements and proposed classification and initiation criteria should prompt discussions to support more equitable access to treatment and better align Australian practice with contemporary evidence and international guidelines.

Characterizing Common Phenotypes Across the Childhood Dementia Disorders: A Cross-sectional Study From Two Australian Centers

BACKGROUND

Childhood dementias are a group of rare pediatric conditions characterized by progressive neurocognitive decline. Quantifying and characterising phenotypes to identify similarities between specific conditions is critical to inform opportunities to optimize care and advance research.

METHODS

This cross-sectional study recruited primary caregivers of children (<18 years) living with a dementia syndrome from neurology and metabolic clinics in Sydney and Adelaide, Australia. Sociodemographic and clinical data were collated. Behavior, eating, sleep, pain, and neurological disability were assessed using validated tools, including Strengths and Difficulties, Child Eating Behaviour, and Children's Sleep Habits questionnaires and visual analog of pain and modified Rankin scales. Data were analyzed with descriptive statistics.

RESULTS

Among 45 children with 23 different dementia syndromes, the modified Rankin Scale demonstrated at least moderate neurological disability and functional dependence in 82% (37/45). Families reported delays in receiving an accurate diagnosis following initial symptoms (mean: 1.6 ± 1.4 years, range: 0-5 years). The most prevalent phenotypes included communication, comprehension, or recall difficulties (87%, 39/45); disturbances in sleep (80%, 36/45); appetite changes (74%, 29/39); mobility issues (53%, 24/45); and hyperactive behavior (53%, 21/40). Behavioral problems had a "high" or "very high" impact on everyday family life in 73% (24/33).

CONCLUSIONS

Childhood dementia disorders share substantial behavioral, motor, sensory, and socioemotional symptoms, resulting in high care needs, despite their vast heterogeneity in age of onset and progression. Considering their unifying characteristics under one collective term is an opportunity to improve treatment, provide quality care, and accelerate research.

Multidisciplinary Management of Rett Syndrome: Twenty Years' Experience

Over the last 20 years, the understanding and natural history of Rett syndrome has advanced, but to date no cure has emerged, with multidisciplinary management being symptomatic and supportive. This study provides a comprehensive review of the clinical features, comorbidities and multidisciplinary management of a well-characterized cohort of females with classical Rett syndrome. We aim to improve awareness and understanding of Rett syndrome amongst pediatricians, pediatric subspecialists and allied health professionals to enable early diagnosis and a streamlined enrolment approach for future clinical trials. Rett syndrome, a complex X-linked condition, affecting mainly females, is due to pathogenic variants of the MECP2 gene in most affected individuals. The Rett syndrome Multidisciplinary Management clinic at The Children's Hospital at Westmead, Sydney, Australia, was established in 2000. This retrospective analysis of individuals who attended the clinic from 2000 to 2020 was performed to identify the incidence and predicted age of onset of Rett syndrome related comorbidities, disease progression and to review management principles. Data collected included age of Rett syndrome diagnosis, MECP2 genotype, clinical features and medical comorbidities, such as sleep disturbance, seizures, breathing irregularities, scoliosis, mobility, hand stereotypies, hand function, constipation, feeding ability, use of gastrostomy, communication skills, QTc prolongation, anthropometry, and bruxism. Analysis of 103 girls who fulfilled the clinical diagnostic criteria for classical Rett syndrome with a pathogenic variant of the MECP2 gene showed a median age of diagnosis of 3 years. The most frequent MECP2 variant was c.502 C>T.

Keeping you on your toes: Smith-Lemli-Opitz Syndrome is an easily missed cause of developmental delays

Smith-Lemli-Opitz syndrome (SLOS) is a relatively common genetic cause of developmental delay and may only present in conjunction with 2,3 toe syndactyly. This case series illustrates a milder phenotype of SLOS, where the predominant findings are neurocognitive in the presence of 2,3 toe syndactyly.

Findings from the Morquio A Registry Study (MARS) after 6 years: Long-term outcomes of MPS IVA patients treated with elosulfase alfa

BACKGROUND

The Morquio A Registry Study (MARS) is an ongoing, multinational, observational study of patients with MPS IVA. Key objectives of MARS are to characterize the heterogeneity and natural history of disease and to evaluate long-term effectiveness and safety of elosulfase alfa enzyme replacement therapy (ERT). Enrollment began in September 2014; data on medical history, clinical outcomes, and safety assessments are collected as part of routine care.

RESULTS

As of February 2021, 381 subjects from 17 countries had enrolled in MARS: 58 ERT-naïve subjects and 323 ERT-treated subjects (≥1 infusion), with a mean ERT exposure of 5.5 years (SD 2.8) and median age at first ERT treatment of 9.8 years. ERT-treated subjects were younger at diagnosis (median 3.4 vs 6.5 years) relative to ERT-naïve subjects. Among ERT-treated subjects, urinary keratan sulfate (uKS) levels declined from pre-ERT baseline to last follow-up on treatment (mean % change [95% confidence interval]: -52.5% [-57.5%, -47.4%]; n = 115) and 6-min walk test distance remained stable (mean change: -6.1 [-27.6, 15.5] m; n = 131) over a mean follow-up of 5.5 years. Forced expiratory volume in 1 s (FEV₁) and forced vital capacity (FVC) increased in subjects who were < 18 years of age at ERT initiation (mean change: +0.3 [0.1, 0.4] L and + 0.4 [0.3, 0.5] L; mean follow-up: ∼6 years; n = 82) and were stable in subjects ≥18 years (mean change: 0.0 [-0.0, 0.1] L and 0.0 [-0.1, 0.1] L; mean follow-up: 4.6 years; n = 38). Overall, 148 (47.1%) ERT-treated subjects experienced ≥1 adverse event (AE) and 110 subjects (35%) reported ≥1 serious AE. Drug-related AEs were reported in 39 (12.4%) subjects; the most common were hypersensitivity (9 subjects [2.9%]), urticaria (8 subjects [2.5%]), and pyrexia (7 subjects [2.2%]).

CONCLUSIONS

MARS is the longest and largest observational study of MPS IVA patients to date, with a heterogenous population that is representative of the MPS IVA population overall. Data collected over the first 6 years of MARS provide real-world evidence for long-term stabilization of endurance and respiratory function among ERT-treated patients, with no new safety concerns identified.

The relationship between beta-ureidopropionase deficiency due to UPB1 variants and human phenotypes is uncertain

BACKGROUND

Beta-ureidopropionase deficiency, caused by variants in UPB1, has been reported in association with various neurodevelopmental phenotypes including intellectual disability, seizures and autism.

AIM

We aimed to reassess the relationship between variants in UPB1 and a clinical phenotype.

METHODS

Literature review, calculation of carrier frequencies from population databases, long-term follow-up of a previously published case and reporting of additional cases.

RESULTS

Fifty-three published cases were identified, and two additional cases are reported here. Of these, 14 were asymptomatic and four had transient neurological features; clinical features in the remainder were variable and included non-neurological presentations. Several of the variants previously reported as pathogenic are present in population databases at frequencies higher than expected for a rare condition. In particular, the variant most frequently reported as pathogenic, p.Arg326Gln, is very common among East Asians, with a carrier frequency of 1 in 19 and 1 in 907 being homozygous for the variant in gnomAD v2.1.1.

CONCLUSION

Pending the availability of further evidence, UPB1 should be considered a 'gene of uncertain clinical significance'. Caution should be used in ascribing clinical significance to biochemical features of beta-ureidopropionase deficiency and/or UPB1 variants in patients with neurodevelopmental phenotypes. UPB1 is not currently suitable for inclusion in gene panels for reproductive genetic carrier screening.

SYNOPSIS

The relationship between beta-ureidopropionase deficiency due to UPB1 variants and clinical phenotypes is uncertain.

Gene Editing and Rett Syndrome: Does It Make the Cut?

Rett syndrome (RTT) is a rare neurogenetic disorder caused by pathogenic variants of the Methyl CpG binding protein 2 (MECP2) gene. The RTT is characterized by apparent normal early development followed by regression of communicative and fine motor skills. Comorbidities include epilepsy, severe cognitive impairment, and autonomic and motor dysfunction. Despite almost 60 clinical trials and the promise of a gene therapy, no cure has yet emerged with treatment remaining symptomatic. Advances in understanding RTT has provided insight into the complexity and exquisite control of MECP2 expression, where loss of expression leads to RTT and overexpression leads to MECP2 duplication syndrome. Therapy development requires regulated expression that matches the spatiotemporal endogenous expression of MECP2 in the brain. Gene editing has revolutionized gene therapy and promises an exciting strategy for many incurable monogenic disorders, including RTT, by editing the native locus and retaining endogenous gene expression. Here, we review the literature on the currently available editing technologies and discuss their limitations and applicability to the treatment of RTT.

FGF21 outperforms GDF15 as a diagnostic biomarker of mitochondrial disease in children

Several studies have shown serum fibroblast growth factor 21 (FGF21) and growth differentiation factor 15 (GDF15) levels are elevated in patients with mitochondrial disease (MD) where myopathy is a feature. In this study we investigated the utility of FGF21 and GDF15 as biomarkers for MD in a phenotypically and genotypically diverse pediatric cohort with suspected MD against a panel of healthy controls and non-mitochondrial disease controls with some overlapping clinical features. Serum was collected from 56 children with MD, 104 children with non-mitochondrial disease (27 neuromuscular, 26 cardiac, 21 hepatic, 30 renal) and 30 pediatric controls. Serum FGF21 and GDF15 concentrations were measured using ELISA, and their ability to detect MD was determined. Median FGF21 and GDF15 serum concentrations were elevated 17-fold and 3-fold respectively in pediatric MD patients compared to the healthy control group. Non-mitochondrial disease controls had elevated serum GDF15 concentrations while FGF21 concentrations were in the normal range. Elevation of GDF15 in a range of non-mitochondrial pediatric disorders limits its use as a MD biomarker. FGF21 was elevated in MD patients with a spectrum of clinical phenotypes, including those without myopathy. Serum FGF21 had an area under the receiver operating characteristic curve of 0.87, indicating good ability to discriminate between pediatric MD and healthy and non-mitochondrial disease controls. Triaging of pediatric MD patients by clinical phenotyping and serum FGF21 testing, followed by massively parallel sequencing, may enable more rapid diagnosis of pediatric MD.

Patient Care Standards for Primary Mitochondrial Disease in Australia. An Australian adaptation of the Mitochondrial Medicine Society recommendations

This document provides consensus‐based recommendations for general physicians and primary care physicians who diagnose and manage patients with mitochondrial diseases (MD). It builds on previous international guidelines, with particular emphasis on clinical management in the Australian setting. This statement was prepared by a working group of medical practitioners, nurses and allied health professionals with clinical expertise and experience in managing Australian patients with MD. As new treatments and management plans emerge, these consensus‐based recommendations will continue to evolve, but current standards of care are summarised in this document.

Liver transplantation in children with inborn errors of metabolism: 30 years experience in NSW, Australia

BACKGROUND

Inborn errors of metabolism (IEM) are a diverse group of genetic disorders that can result in significant morbidity and sometimes death. Metabolic management can be challenging and burdensome for families. Liver transplantation (LT) is increasingly being considered a treatment option for some IEMs. IEMs are now considered the second most common reason for pediatric LT.

AIM

To review the data of all children with an IEM who had LT at The Children's Hospital at Westmead (CHW), NSW, Australia between January 1986 and January 2019.

METHODS

Retrospective data collected from the medical records and genetic files included patient demographics, family history, parental consanguinity, method of diagnosis of IEM, hospital and intensive care unit admissions, age at LT, graft type, clinical outcomes and metabolic management pre and post-LT.

RESULTS

Twenty-four LT were performed for 21 patients. IEM diagnoses were MSUD (n = 4), UCD (n = 8), OA (n = 6), TYR type I (n = 2) and GSD Ia (n = 1). Three patients had repeat transplants due to complications. Median age at transplant was 6.21 years (MSUD), 0.87 years (UCD), 1.64 years (OA) and 2.2 years (TYR I). Two patients died peri-operatively early in the series, one died 3 months after successful LT due to septicemia. Eighteen LTs have been performed since 2008 in comparison to six LT prior to 2008. Dietary management was liberalized post LT for all patients.

CONCLUSIONS

Referral for LT for IEMs has increased over the last 33 years, with the most referrals in the last 10 years. Early LT has resulted in improved clinical outcomes and patient survival.

Neutropenia and intellectual disability are hallmarks of biallelic and de novo CLPB deficiency

PURPOSE

To investigate monoallelic CLPB variants. Pathogenic variants in many genes cause congenital neutropenia. While most patients exhibit isolated hematological involvement, biallelic CLPB variants underlie a neurological phenotype ranging from nonprogressive intellectual disability to prenatal encephalopathy with progressive brain atrophy, movement disorder, cataracts, 3-methylglutaconic aciduria, and neutropenia. CLPB was recently shown to be a mitochondrial refoldase; however, the exact function remains elusive.

METHODS

We investigated six unrelated probands from four countries in three continents, with neutropenia and a phenotype dominated by epilepsy, developmental issues, and 3-methylglutaconic aciduria with next-generation sequencing.

RESULTS

In each individual, we identified one of four different de novo monoallelic missense variants in CLPB. We show that these variants disturb refoldase and to a lesser extent ATPase activity of CLPB in a dominant-negative manner. Complexome profiling in fibroblasts showed CLPB at very high molecular mass comigrating with the prohibitins. In control fibroblasts, HAX1 migrated predominantly as monomer while in patient samples multiple HAX1 peaks were observed at higher molecular masses comigrating with CLPB thus suggesting a longer-lasting interaction between CLPB and HAX1.

CONCLUSION

Both biallelic as well as specific monoallelic CLPB variants result in a phenotypic spectrum centered around neurodevelopmental delay, seizures, and neutropenia presumably mediated via HAX1.

Treatable lysosomal storage diseases in the advent of disease-specific therapy

Lysosomal storage diseases (LSD) comprise a rare and heterogeneous group of nearly 50 heritable metabolic disorders caused by mutations in proteins critical for cellular lysosomal function. Defects in the activity of these proteins in multiple organs leads to progressive intra-lysosomal accumulation of specific substrates, resulting in disruption of cellular functions, extracellular inflammatory responses, tissue damage and organ dysfunction. The classification and clinical presentation of different LSD are dependent on the type of accumulated substrate. Some clinical signs and symptoms are common across multiple LSD, while others are more specific to a particular syndrome. Due to the rarity and wide clinical diversity of LSD, identification and diagnosis can be challenging, and in many cases diagnosis is delayed for months or years. Treatments, such as enzyme replacement therapy, haemopoietic stem cell transplantation and substrate reduction therapy, are now available for some of the LSD. For maximum effect, therapy must be initiated prior to the occurrence of irreversible tissue damage, highlighting the importance of prompt diagnosis. Herein, we discuss the clinical presentation, diagnosis and treatment of four of the treatable LSD: Gaucher disease, Fabry disease, Pompe disease, and two of the mucopolysaccharidoses (I and II). For each disease, we present illustrative case studies to help increase awareness of their clinical presentation and possible treatment outcomes.

Familial DHCR7 genotype presenting as a very mild form of Smith-Lemli-Opitz syndrome and lethal holoprosencephaly

Smith-Lemli-Opitz syndrome (SLOS) is an autosomal recessive metabolic disorder caused by variants in the DHCR7 gene. In cholesterol biosynthesis, 7-dehydrocholesterol (7-DHC) is converted to cholesterol by the enzyme 7-DHC reductase, which is encoded by the gene DHCR7. Thus, an elevated 7-DHC is indicative of SLOS. Characteristically SLOS is usually associated with congenital anomalies, dysmorphisms, and moderate to severe neurodevelopmental delay. However, there are rare descriptions of individuals with milder phenotypes. We report a mild case of SLOS presenting with short stature, cleft palate, imperforate anus, and mild language delay with subtle dysmorphic features. 7-DHC was not elevated at 1 year of age and SLOS considered excluded at this time. The parents had two pregnancies with holoprosencephaly. Whole exome sequencing of one of the fetuses identified compound heterozygous pathogenic variants in the DHCR7 gene (c.964-1G>C (p.?) and c.1039G>A (p.Gly347Ser) causative of SLOS. The proband with a mild form of SLOS was also found to have the same DHCR7 variants as the fetus and repeat testing of 7-DHC at 4 years of age was elevated, in keeping with SLOS. This case is the first to describe a wide intrafamilial phenotypic spectrum of SLOS as a result of the same DHCR7 genotype. This case also supports the findings of others that a normal or near normal development should not exclude SLOS. As demonstrated in this case exclusion of a metabolic diagnosis because of a negative biochemical marker such as 7-DHC is not absolute and if clinical suspicion remains genomic sequencing is warranted.

Neuronal ceroid lipofuscinosis type 2: an Australian case series

AIM

Late infantile neuronal ceroid lipofuscinosis type 2 (CLN2) disease is a rare neurodegenerative disorder presenting in children aged 2-4 years with seizures and loss of motor and language skills, followed by blindness and death in late childhood. Initial presenting features are similar to a range of common epilepsies. We aim to highlight typical clinical and radiological features that may prompt diagnosis of CLN2 disease in early disease stages.

METHODS

We present a series of 13 Australian patients with CLN2 disease, describing clinical features, disease evolution, neuroimaging, electroencephalogram, biochemical and genetic results. Expert neuroradiological magnetic resonance imaging (MRI) analysis was retrospectively performed on 10 cases.

RESULTS

Twelve patients presented with seizures, with initial seizures being focal (n = 4), generalised tonic-clonic (n = 3), absence (n = 3) and febrile (n = 2). Eleven patients (85%) had a language delay before the onset of seizures. Cerebellar or cerebral atrophy was noted in all patients on centralised MRI review, with abnormalities of the brain-stem, ventricles, corpus callosum and hippocampi.

CONCLUSIONS

Early language delay with the onset of seizures at 2-4 years of age is the hallmark of CLN2 disease. MRI findings of early subtle atrophy in the cerebellum or posterior cortical regions should hasten testing for CLN2 disease to enable early initiation of enzyme replacement therapy.

Expansion of the phenotypic spectrum of de novo missense variants in kinesin family member 1A (KIF1A)

Defects in the motor domain of kinesin family member 1A (KIF1A), a neuron-specific ATP-dependent anterograde axonal transporter of synaptic cargo, are well-recognized to cause a spectrum of neurological conditions, commonly known as KIF1A-associated neurological disorders (KAND). Here, we report one mutation-negative female with classic Rett syndrome (RTT) harboring a de novo heterozygous novel variant [NP_001230937.1:p.(Asp248Glu)] in the highly conserved motor domain of KIF1A. In addition, three individuals with severe neurodevelopmental disorder along with clinical features overlapping with KAND are also reported carrying de novo heterozygous novel [NP_001230937.1:p.(Cys92Arg) and p.(Pro305Leu)] or previously reported [NP_001230937.1:p.(Thr99Met)] variants in KIF1A. In silico tools predicted these variants to be likely pathogenic, and 3D molecular modeling predicted defective ATP hydrolysis and/or microtubule binding. Using the neurite tip accumulation assay, we demonstrated that all novel KIF1A variants significantly reduced the ability of the motor domain of KIF1A to accumulate along the neurite lengths of differentiated SH-SY5Y cells. In vitro microtubule gliding assays showed significantly reduced velocities for the variant p.(Asp248Glu) and reduced microtubule binding for the p.(Cys92Arg) and p.(Pro305Leu) variants, suggesting a decreased ability of KIF1A to move along microtubules. Thus, this study further expanded the phenotypic characteristics of KAND individuals with pathogenic variants in the KIF1A motor domain to include clinical features commonly seen in RTT individuals.

Fatal perinatal mitochondrial cardiac failure caused by recurrent de novo duplications in the ATAD3 locus

Background

In about half of all patients with a suspected monogenic disease, genomic investigations fail to identify the diagnosis. A contributing factor is the difficulty with repetitive regions of the genome, such as those generated by segmental duplications. The ATAD3 locus is one such region, in which recessive deletions and dominant duplications have recently been reported to cause lethal perinatal mitochondrial diseases characterized by pontocerebellar hypoplasia or cardiomyopathy, respectively.

Methods

Whole exome, whole genome and long-read DNA sequencing techniques combined with studies of RNA and quantitative proteomics were used to investigate 17 subjects from 16 unrelated families with suspected mitochondrial disease.

Findings

We report six different de novo duplications in the ATAD3 gene locus causing a distinctive presentation including lethal perinatal cardiomyopathy, persistent hyperlactacidemia, and frequently corneal clouding or cataracts and encephalopathy. The recurrent 68 Kb ATAD3 duplications are identifiable from genome and exome sequencing but usually missed by microarrays. The ATAD3 duplications result in the formation of identical chimeric ATAD3A/ATAD3C proteins, altered ATAD3 complexes and a striking reduction in mitochondrial oxidative phosphorylation complex I and its activity in heart tissue.

Conclusions

ATAD3 duplications appear to act in a dominant-negative manner and the de novo inheritance infers a low recurrence risk for families, unlike most pediatric mitochondrial diseases. More than 350 genes underlie mitochondrial diseases. In our experience the ATAD3 locus is now one of the five most common causes of nuclear-encoded pediatric mitochondrial disease but the repetitive nature of the locus means ATAD3 diagnoses may be frequently missed by current genomic strategies.

Funding

Australian NHMRC, US Department of Defense, Japanese AMED and JSPS agencies, Australian Genomics Health Alliance and Australian Mito Foundation.

Is it Pompe Disease? Australian diagnostic considerations

Pompe Disease is a spectrum disorder with an evolving phenotype in which diagnostic delay is common. Contributing factors include the rarity of the disorder, its wide clinical spectrum, signs and symptoms that overlap with those of other neuromuscular disorders, variable diagnostic approaches, lack of awareness of the clinical manifestations and difficulties in completing the diagnostic inventory. International updates and recommendations have been published providing diagnostic guidelines and management criteria. However, questions remain in the Australian setting. A panel (two neurologists, one clinical geneticist) reviewed the literature, examined clinical questions of relevance to the Australian setting, and developed a framework for the guidance. A wider panel, comprising the initial panel plus eight additional members, critiqued the framework and contributed clinical guidance within the scope of their respective areas of clinical expertise. The resultant expert consensus recommendations build on currently available data to propose an appropriate management framework incorporating the diagnosis, classification, therapeutic approach, multidisciplinary care, and on-going monitoring of patients with Pompe Disease in the Australian setting. It is hoped that diagnostic delay can be reduced with appropriate recourse to evidence-based insights and practical advice on diagnosis and management tailored to the Australian setting.

Hypoglycemia in CDG patients due to PMM2 mutations: Follow up on hyperinsulinemic patients

BACKGROUND

Phosphomannomutase 2 deficiency (PMM2-CDG) is the most common congenital disorder of glycosylation (CDG). Hypoglycemia has been reported in various CDG including PMM2-CDG. The frequency and etiology of hypoglycemia in PMM2-CDG are not well studied.

METHODS

We conducted a systematic review of the literature on genetically and/or biochemically confirmed PMM2-CDG patients who developed hypoglycemia. Prospective follow-up information on the patients who received diazoxide therapy was collected and evaluated.

RESULTS

A total of 165 peer-reviewed articles reporting on 933 PMM2-CDG patients were assessed. Hypoglycemia was specifically mentioned only in 23 of these patients (2.5%). Hyperinsulinism was identified in 10 patients (43% of all hypoglycemic patients). Among these 10 patients, seven were successfully treated with diazoxide. However, most patients remained on therapy longer than a year to stay free of hypoglycemia.

CONCLUSION

Hypoglycemia is a rarely reported finding in patients with PMM2-CDG. Diazoxide-responsive hyperinsulinism was found to have a good prognosis on medication in our PMM2-CDG patients with hypoglycemia. No genotype-phenotype correlation was observed with respect to hyperinsulinism. A prospective study should be undertaken to explore the hypothesis that hypoglycemia is underdiagnosed in PMM2-CDG and to evaluate whether hyperinsulinism is always associated with hypoglycemia.

Whole exome sequencing reveals a de novo missense variant in EEF1A2 in a Rett syndrome-like patient

Using whole exome sequencing, we found a pathogenic variant in the EEF1A2 gene in a patient with a Rett syndrome-like (RTT-like) phenotype, further confirming the association between EEF1A2 and Rett syndrome RTT and RTT-like phenotypes.

The incidence, prevalence and clinical features of MECP2 duplication syndrome in Australian children

AIM

The aim of this study was to assess the incidence and prevalence of MECP2 duplication syndrome in Australian children and further define its phenotype.

METHODS

The Australian Paediatric Surveillance Unit was used to identify children with MECP2 duplication syndrome between June 2014 and November 2017. Reporting clinicians were invited to complete a questionnaire. Clinician data (n = 20) were supplemented with information from the International Rett Syndrome Phenotype Database and from caregivers (n = 7). Birth prevalence and diagnostic incidence were calculated.

RESULTS

The birth prevalence of MECP2 duplication syndrome in Australia was 0.65/100 000 for all live births and 1/100 000 for males. Diagnostic incidence was 0.07/100 000 person-years overall and 0.12/100 000 person-years for males. The median age at diagnosis was 23.5 months (range 0 months-13 years). A history of pneumonia was documented in three quarters of the clinical cases, half of whom had more than nine episodes. Cardiovascular abnormalities were reported in three cases. A clinical vignette is presented for one child who died due to severe idiopathic pulmonary hypertension. The majority (13/15) of males had inherited the duplication from their mothers, and two had an unbalanced translocation.

CONCLUSIONS

MECP2 duplication syndrome is a rare but important diagnosis in children because of the burden of respiratory illness and recurrence risk. Pulmonary hypertension is a rare life-threatening complication. Array comparative genomic hybridisation testing is recommended for children with undiagnosed intellectual disability or global developmental delay. Early cardiac assessment and ongoing monitoring is recommended for MECP2 duplication syndrome.

Genome-wide transcriptomic and proteomic studies of Rett syndrome mouse models identify common signaling pathways and cellular functions as potential therapeutic targets

The discovery that Rett syndrome is caused by mutations in the MECP2 gene has provided a major breakthrough in our understanding of the disorder. However, despite this, there is still limited understanding of the underlying pathophysiology of the disorder hampering the development of curative treatments. Over the years, a number of animal models have been developed contributing to our knowledge of the role of MECP2 in development and improving our understanding of how subtle expression levels affect brain morphology and function. Transcriptomic and proteomic studies of animal models are useful in identifying perturbations in functional pathways and providing avenues for novel areas of research into disease. This review focuses on published transcriptomic and proteomic studies of mouse models of Rett syndrome with the aim of providing a summary of all the studies, the reported dysregulated genes and functional pathways that are found to be perturbed. The 36 articles identified highlighted a number of dysfunctional pathways as well as perturbed biological networks and cellular functions including synaptic dysfunction and neuronal transmission, inflammation, and mitochondrial dysfunction. These data reveal biological insights that contribute to the disease process which may be targeted to investigate curative treatments.

NAD(P)HX dehydratase (NAXD) deficiency: a novel neurodegenerative disorder exacerbated by febrile illnesses

Physical stress, including high temperatures, may damage the central metabolic nicotinamide nucleotide cofactors [NAD(P)H], generating toxic derivatives [NAD(P)HX]. The highly conserved enzyme NAD(P)HX dehydratase (NAXD) is essential for intracellular repair of NAD(P)HX. Here we present a series of infants and children who suffered episodes of febrile illness-induced neurodegeneration or cardiac failure and early death. Whole-exome or whole-genome sequencing identified recessive NAXD variants in each case. Variants were predicted to be potentially deleterious through in silico analysis. Reverse-transcription PCR confirmed altered splicing in one case. Subject fibroblasts showed highly elevated concentrations of the damaged cofactors S-NADHX, R-NADHX and cyclic NADHX. NADHX accumulation was abrogated by lentiviral transduction of subject cells with wild-type NAXD. Subject fibroblasts and muscle biopsies showed impaired mitochondrial function, higher sensitivity to metabolic stress in media containing galactose and azide, but not glucose, and decreased mitochondrial reactive oxygen species production. Recombinant NAXD protein harbouring two missense variants leading to the amino acid changes p.(Gly63Ser) and p.(Arg608Cys) were thermolabile and showed a decrease in Vmax and increase in KM for the ATP-dependent NADHX dehydratase activity. This is the first study to identify pathogenic variants in NAXD and to link deficient NADHX repair with mitochondrial dysfunction. The results show that NAXD deficiency can be classified as a metabolite repair disorder in which accumulation of damaged metabolites likely triggers devastating effects in tissues such as the brain and the heart, eventually leading to early childhood death.

Cryptic intronic NBAS variant reveals the genetic basis of recurrent liver failure in a child

BACKGROUND

In almost half of patients with acute liver failure the cause is unknown, making targeted treatment and decisions about liver transplantation a challenge. Monogenic disorders may contribute to a significant proportion of these undiagnosed patients, and so the incorporation of technologies such as next generation sequencing (NGS) in the clinic could aid in providing a definitive diagnosis. However, this technology may present a major challenge in interpretation of sequence variants, particularly those in non-coding regions.

RESULTS

In this report we describe a case of Infantile liver failure syndrome 2 (ILFS2; MIM 616483) due to novel bi-allelic variants in the NBAS gene. A missense variant NM_015909.3(NBAS):c.2617C > T, NP_056993.2(NBAS):p.(Arg873Trp) was identified by whole genome sequencing (WGS). By combining WGS and reverse transcription-polymerase chain reaction (RT-PCR) we were able to identify a novel deep intronic variant, NM_015909.3(NBAS):c.2423 + 404G > C, leading to the inclusion of a pseudo-exon. This mechanism has not been described previously in this syndrome.

CONCLUSIONS

This study highlights the utility of analyzing NGS data in conjunction with investigating complementary DNA (cDNA) using techniques such as RT-PCR for detection of variants that otherwise would be likely to be missed in common NGS bioinformatic analysis pipelines. Combining these approaches, particularly when the phenotype match is strong, could lead to an increase in the diagnostic yield in acute liver failure and thus aid in targeted treatment, accurate genetic counseling and restoration of reproductive confidence.

Infantile-onset Pompe disease: A case series highlighting early clinical features, spectrum of disease severity and treatment response

AIM

Pompe disease is a rare, autosomal, recessive disorder. Alterations in the gene encoding lysosomal acid alpha-glucosidase cause impaired glycogen degradation and resultant lysosomal glycogen accumulation. Classic infantile-onset Pompe disease (IPD) manifests soon after birth, severe cases have complete/near complete enzyme deficiency. IPD is associated with a broad spectrum of non-specific clinical features, and diagnostic delays are common. Without treatment, death typically occurs within the first 2 years of life. We present case experiences to help expand paediatricians' understanding of factors contributing to diagnostic delay, clinical decline and to highlight the need for timely therapy.

METHODS

Data were extracted from IPD cases managed at our hospital. Key aspects of clinical presentation, diagnosis, genetic variations, management and overall outcomes were collated then compared with what is already known in the literature.

RESULTS

We report four IPD cases (three female). Two patients were cross-reactive immunological material negative. Age at symptom onset was 3-9 months, presenting clinical features were varied, and confirmatory diagnosis was significantly delayed in one patient. In concert with the literature, cardiomegaly, ventricular hypertrophy and delayed developmental milestones were seen in all four cases. Our cases demonstrate a range of disease severity, response to enzyme replacement therapy and antibody development. Significant immune responses were seen in two cases (one cross-reactive immunological material positive); despite immunomodulation therapy, both were associated with fatal outcomes.

CONCLUSION

Timely diagnosis and initiation of enzyme replacement therapy is critical to patient outcomes as IPD progresses rapidly and irreversible changes in clinical status may occur during the delay.

Impact of Gastrostomy Placement on Nutritional Status, Physical Health, and Parental Well-Being of Females with Rett Syndrome: A Longitudinal Study of an Australian Population

OBJECTIVES

To evaluate how age-related trends in nutritional status, physical health, and parental well-being in females with Rett syndrome may be related to gastrostomy placement and to examine the impact of the procedure on mortality.

STUDY DESIGN

We included 323 females from the Australian Rett Syndrome Study and analyzed their demographic, genetic, and child and parental health data collected from over 6 waves of follow-up questionnaire between 2000 and 2011. We used mixed-effects models to estimate the association between repeated measures of outcomes and age, gastrostomy placement and their interaction and Cox proportional hazards regression models to estimate relative risks of mortality for individuals with gastrostomy.

RESULTS

Nearly one-third (30.3%) of the cases underwent gastrostomy placement. Nutritional status based on weight, height, and body mass index (BMI) improved over time, and BMI was greater in individuals with gastrostomy placement than in those without (adjusted β = 0.87, 95% CI 0.02-1.73). There was no association between gastrostomy placement and individual's physical health outcomes or parental physical and mental health, nor did the age trend of these outcomes vary by gastrostomy insertion status. Nevertheless, among those at risk of suboptimal weight, the all-cause mortality rate was greater in those who had gastrostomy placement compared with those who had not (hazard ratio 4.07, 95% CI 1.96-8.45).

CONCLUSION

Gastrostomy placement was associated with improvement in BMI in females with Rett syndrome, but its long-term impact on individuals and their families is unclear.

Effectiveness of Early Hematopoietic Stem Cell Transplantation in Preventing Neurocognitive Decline in Mucopolysaccharidosis Type II: A Case Series

The early progressive form of the X-linked disorder, Hunter syndrome or mucopolysaccharidosis type II (MPS II) (OMIM #309900), is characterized by cognitive decline, and pulmonary and cardiac complications that often cause death before 20 years of age. Deficiency of the lysosomal enzyme, iduronate-2-sulfatase (EC 3.1.6.13) results in deposition of the glycosaminoglycans, dermatan, and heparan sulfate in various tissues. In recent years, enzyme replacement therapy (ERT) has become the mainstay of treatment, but is expensive and ineffective in arresting cognitive decline. Hematopoietic stem cell transplantation (HSCT) also provides enzyme replacement, and may be effective in stabilizing neurocognitive function if initiated early, though data are limited. We present a case series of four patients who demonstrated neurocognitive stabilization with early HSCT. HSCT is a potentially underutilized treatment strategy for select groups of MPS II patients.

Whole-exome sequencing reanalysis at 12 months boosts diagnosis and is cost-effective when applied early in Mendelian disorders

PURPOSE

Whole-exome sequencing (WES) has revolutionized Mendelian diagnostics, however, there is no consensus on the timing of data review in undiagnosed individuals and only preliminary data on the cost-effectiveness of this technology. We aimed to assess the utility of WES data reanalysis for diagnosis in Mendelian disorders and to analyze the cost-effectiveness of this technology compared with a traditional diagnostic pathway.

METHODS

WES was applied to a cohort of 54 patients from 37 families with a variety of Mendelian disorders to identify the genetic etiology. Reanalysis was performed after 12 months with an improved WES diagnostic pipeline. A comparison was made between costs of a modeled WES pathway and a traditional diagnostic pathway in a cohort with intellectual disability (ID).

RESULTS

Reanalysis of WES data at 12 months improved diagnostic success from 30 to 41% due to interim publication of disease genes, expanded phenotype data from referrer, and an improved bioinformatics pipeline. Cost analysis on the ID cohort showed average cost savings of US$586 (AU$782) for each additional diagnosis.

CONCLUSION

Early application of WES in Mendelian disorders is cost-effective and reanalysis of an undiagnosed individual at a 12-month time point increases total diagnoses by 11%.

Rett Syndrome: A Genetic Update and Clinical Review Focusing on Comorbidities

Rett syndrome (RTT) is a unique neurodevelopmental disorder that primarily affects females resulting in severe cognitive and physical disabilities. Despite the commendable collective efforts of the research community to better understand the genetics and underlying biology of RTT, there is still no cure. However, in the past 50 years, since the first report of RTT, steady progress has been made in the accumulation of clinical and molecular information resulting in the identification of a number of genes associated with RTT and associated phenotypes, improved diagnostic criteria, natural history studies, curation of a number of databases capturing genotypic and phenotypic data, a number of promising clinical trials and exciting novel therapeutic options which are currently being tested in laboratory and clinical settings. This Review focuses on the current knowledge of the clinical aspects of RTT, with particular attention being paid to clinical trials and the comorbidities of the disorder as well as the genetic etiology and the recognition of new diseases genes.

Split-graft liver transplantation from an adult donor with an unrecognized UCD to a pediatric and adult recipient

We report the outcomes of an adult and pediatric split liver transplant from an adult male donor who died due to an unrecognized UCD, OTC deficiency. Recognizing inborn errors of metabolism can be challenging, especially in adult centers where such disorders are rarely encountered. Shortage of donors for liver transplantation has led to procedures to maximize donor utilization, such as split and live donor grafts. The cause of death should be ascertained before accepting a cadaveric donor organ.

Family satisfaction following spinal fusion in Rett syndrome

PURPOSE

We evaluated family satisfaction following spinal fusion in girls with Rett syndrome.

METHODS

Families participating in the population-based and longitudinal Australian Rett Syndrome Database whose daughter had undergone spinal fusion provided data on satisfaction overall, care processes and expected changes in health and function. Content analysis of responses to open-ended questions was conducted.

RESULTS

Families reported high levels of overall satisfaction and consistently high ratings in relation to surgical and ICU care. Outstanding clinical care and the development of strong partnerships with clinical staff were much appreciated by families, whereas poor information exchange and inconsistent care caused concerns.

CONCLUSIONS

Family satisfaction is an important outcome within a patient-centred quality of care framework. Our findings suggest strategies to inform the delivery of care in relation to spinal fusion for Rett syndrome and could also inform the hospital care of other children with disability and a high risk of hospitalization.

Expanding the clinical picture of the MECP2 Duplication syndrome

Individuals with two or more copies of the MECP2 gene, located at Xq28, share clinical features and a distinct facial phenotype known as MECP2 Duplication syndrome. We have examined perinatal characteristics, early childhood development and medical co-morbidities in this disorder. The International Rett Syndrome Phenotype Database (InterRett), which collects information from caregivers and clinicians on individuals with Rett syndrome and MECP2 associated disorders, was used as the data source. Data were available on 56 cases (49 males and 7 females) with MECP2 Duplication syndrome. Median age at ascertainment was 7.9 years (range: 1.2-37.6 years) and at diagnosis 3.0 years (range: 3 weeks-37 years). Less than a third (29%) learned to walk. Speech deterioration was reported in 34% and only 20% used word approximations or better at ascertainment. Over half (55%) had been hospitalised for respiratory infections in the first 2 years of life. Just under half (44%) had seizures, occurring daily in nearly half of this group. The majority (89%) had gastrointestinal problems and a third had a gastrostomy. Following the recent demonstration of phenotype reversal in a mouse model of MECP2 Duplication, a clear understanding of the natural history is crucial to the design and implementation of future therapeutic strategies.

Surgical fusion of early onset severe scoliosis increases survival in Rett syndrome: a cohort study

AIM

Scoliosis is a common comorbidity in Rett syndrome and spinal fusion may be recommended if severe. We investigated the impact of spinal fusion on survival and risk of severe lower respiratory tract infection in Rett syndrome.

METHOD

Data were ascertained from hospital medical records, the Australian Rett Syndrome Database, a longitudinal and population-based registry, and from the Australian Institute of Health and Welfare National Death Index database. Cox regression and generalized estimating equation models were used to estimate the effects of spinal surgery on survival and severe respiratory infection respectively in 140 females who developed severe scoliosis (Cobb angle ≥45°) before adulthood.

RESULTS

After adjusting for mutation type and age of scoliosis onset, the rate of death was lower in the surgery group (hazard ratio [HR] 0.30, 95% confidence interval [CI] 0.12-0.74; p=0.009) compared to those without surgery. Rate of death was particularly reduced for those with early onset scoliosis (HR 0.17, 95% CI 0.06-0.52; p=0.002). There was some evidence to suggest that spinal fusion was associated with a reduction in risk of severe respiratory infection among those with early onset scoliosis (risk ratio 0.41, 95% CI 0.16-1.03; p=0.06).

INTERPRETATION

With appropriate cautions, spinal fusion confers an advantage to life expectancy in Rett syndrome.

Clinical Guidelines for Management of Bone Health in Rett Syndrome Based on Expert Consensus and Available Evidence

OBJECTIVES

We developed clinical guidelines for the management of bone health in Rett syndrome through evidence review and the consensus of an expert panel of clinicians.

METHODS

An initial guidelines draft was created which included statements based upon literature review and 11 open-ended questions where literature was lacking. The international expert panel reviewed the draft online using a 2-stage Delphi process to reach consensus agreement. Items describe the clinical assessment of bone health, bone mineral density assessment and technique, and pharmacological and non-pharmacological interventions.

RESULTS

Agreement was reached on 39 statements which were formulated from 41 statements and 11 questions. When assessing bone health in Rett syndrome a comprehensive assessment of fracture history, mutation type, prescribed medication, pubertal development, mobility level, dietary intake and biochemical bone markers is recommended. A baseline densitometry assessment should be performed with accommodations made for size, with the frequency of surveillance determined according to individual risk. Lateral spine x-rays are also suggested. Increasing physical activity and initiating calcium and vitamin D supplementation when low are the first approaches to optimizing bone health in Rett syndrome. If individuals with Rett syndrome meet the ISCD criterion for osteoporosis in children, the use of bisphosphonates is recommended.

CONCLUSION

A clinically significant history of fracture in combination with low bone densitometry findings is necessary for a diagnosis of osteoporosis. These evidence and consensus-based guidelines have the potential to improve bone health in those with Rett syndrome, reduce the frequency of fractures, and stimulate further research that aims to ameliorate the impacts of this serious comorbidity.

Paediatric Fabry disease

Fabry disease is a rare, progressive X-linked inborn error of the glycosphingolipid metabolic pathway. Mutations of the GLA gene result in deficiency of the lysosomal enzyme, α-galactosidase A (α-Gal A) with accumulation of glycosphingolipids, particularly globotriaosylceramide (GL3) in the vascular endothelium of various tissues. Accumulation of GL3 eventually leads to life threatening renal, cardiac and cerebrovascular complications typically in the third to fifth decades of life. The first signs and symptoms of classic Fabry disease however appear in childhood but diagnosis is often delayed. The symptoms most commonly experienced in childhood include neuropathic pain, gastrointestinal dysfunction, hyperhidrosis and heat intolerance. Timely diagnosis is important as early treatment with enzyme replacement therapy reduces GL3 accumulation, can stabilize disease progression and potentially prevent irreversible organ damage. Physicians should be familiar with the signs and symptoms of Fabry disease in childhood and be particularly vigilant for unusual or non-specific but recurrent or episodic symptoms.

CRIM-negative infantile Pompe disease: characterization of immune responses in patients treated with ERT monotherapy

Purpose

Enzyme replacement therapy (ERT) with recombinant human GAA (rhGAA) prolongs survival in infantile Pompe disease (IPD). However, the majority of cross reactive immunologic material (CRIM)-negative (CN) patients have immune responses with significant clinical decline despite continued ERT. We aimed to characterize immune responses in CN IPD patients receiving ERT monotherapy.

Methods

A chart review identified 20 CN IPD patients treated with ERT monotherapy for ≥6 months. Patients were stratified by anti-rhGAA antibody titers: high sustained antibody titers (HSAT) ≥51,200 at least twice; low titers (LT) <6,400 throughout treatment; or sustained intermediate titers (SIT) 6,400–25,600.

Results

Despite early initiation of treatment, the majority (85%) of CN patients developed significant antibody titers, most with HSAT associated with invasive ventilation and death. Nearly all patients with HSAT had at least one nonsense GAA mutation, while the LT group exclusively carried splice site or frameshift mutations. Only one patient in the HSAT group is currently alive after successful immune modulation in the entrenched setting.

Conclusion

Immunological responses are a significant risk in CN IPD; thus, immune tolerance induction in the naïve setting should strongly be considered. Further exploration of factors influencing immune responses is required, particularly with the advent of newborn screening for Pompe disease.

Experience of gastrostomy using a quality care framework: the example of rett syndrome

Rett syndrome is one of many severe neurodevelopmental disorders with feeding difficulties. In this study, associations between feeding difficulties, age, MECP2 genotype, and utilization of gastrostomy were investigated. Weight change and family satisfaction following gastrostomy were explored. Data from the longitudinal Australian Rett Syndrome Database whose parents provided data in the 2011 family questionnaire (n=229) were interrogated. We used logistic regression to model relationships between feeding difficulties, age group, and genotype. Content analysis was used to analyze data on satisfaction following gastrostomy. In those who had never had gastrostomy and who fed orally (n=166/229), parents of girls<7 years were more concerned about food intake compared with their adult peers (odds ratio [OR] 4.26; 95% confidence interval [CI] 1.29, 14.10). Those with a p.Arg168 mutation were often perceived as eating poorly with nearly a 6-fold increased odds of choking compared to the p.Arg133Cys mutation (OR 5.88; 95% CI 1.27, 27.24). Coughing, choking, or gagging during meals was associated with increased likelihood of later gastrostomy. Sixty-six females (28.8%) had a gastrostomy, and in those, large MECP2 deletions and p.Arg168 mutations were common. Weight-for-age z-scores increased by 0.86 (95% CI 0.41, 1.31) approximately 2 years after surgery. Families were satisfied with gastrostomy and felt less anxious about the care of their child. Mutation type provided some explanation for feeding difficulties. Gastrostomy assisted the management of feeding difficulties and poor weight gain, and was acceptable to families. Our findings are likely applicable to the broader community of children with severe disability.

Recessive mutations in PCBD1 cause a new type of early-onset diabetes

Mutations in several genes cause nonautoimmune diabetes, but numerous patients still have unclear genetic defects, hampering our understanding of the development of the disease and preventing pathogenesis-oriented treatment. We used whole-genome sequencing with linkage analysis to study a consanguineous family with early-onset antibody-negative diabetes and identified a novel deletion in PCBD1 (pterin-4 α-carbinolamine dehydratase/dimerization cofactor of hepatocyte nuclear factor 1 α), a gene that was recently proposed as a likely cause of diabetes. A subsequent reevaluation of patients with mild neonatal hyperphenylalaninemia due to mutations in PCBD1 from the BIODEF database identified three additional patients who had developed HNF1A-like diabetes in puberty, indicating early β-cell failure. We found that Pcbd1 is expressed in the developing pancreas of both mouse and Xenopus embryos from early specification onward showing colocalization with insulin. Importantly, a morpholino-mediated knockdown in Xenopus revealed that pcbd1 activity is required for the proper establishment of early pancreatic fate within the endoderm. We provide the first genetic evidence that PCBD1 mutations can cause early-onset nonautoimmune diabetes with features similar to dominantly inherited HNF1A-diabetes. This condition responds to and can be treated with oral drugs instead of insulin, which is important clinical information for these patients. Finally, patients at risk can be detected through a newborn screening for phenylketonuria.

The trajectories of sleep disturbances in Rett syndrome

Rett syndrome is a rare neurodevelopmental disorder usually affecting females, and is associated with a mutation in the MECP2 gene. Sleep problems occur commonly and we investigated the trajectories and influences of age, mutation and treatments. Data were collected at six time points over 12 years from 320 families registered with the Australian Rett Syndrome Database. Regression analysis was used to investigate relationships between sleep disturbances, age, mutation type and use of treatment, and latent class growth analysis was performed to identify sleep problem phenotypes and model the effect of mutation type. The age range of subjects was 2.0-35.8 years. The study showed that sleep problems occurred in more than 80% of individuals and the prevalence decreased with age. Night laughing and night screaming occurred in 77 and 49%, respectively, when younger. Those with a large deletion had a higher prevalence of night laughing, which often occurred frequently. Treatment was associated with a 1.7% reduction in risk of further sleep problems. High and low baseline prevalence groups were identified. Approximately three-quarters of girls and women with sleep disturbances were in the high baseline group and problems persisted into adulthood. Conversely, 57% with night laughing and 42% with night screaming in the high baseline group exhibited mild improvement over time. Mutation type was not found to be a significant predictor of group membership. In conclusion, the evolution of sleep problems differed between subgroups of girls and women with Rett syndrome, in part explained by age and genotype. Treatment was not associated with improvement in sleep problems.

The Molecular Bases of Phenylketonuria (PKU) in New South Wales, Australia: Mutation Profile and Correlation with Tetrahydrobiopterin (BH4) Responsiveness

Phenylketonuria (PKU) is an autosomal recessive inborn error of phenylalanine metabolism predominantly caused by mutations in the phenylalanine hydroxylase (PAH) gene. Mutation screening was carried out in a large cohort of PKU patients from New South Wales, Australia. Pathogenic mutations were identified in 99% of the alleles screened, with the two most common mutations (p.R408W and IVS12+1G>A) accounting for 30.7% of alleles. Most individuals were compound heterozygotes for previously reported mutations, but four novel mutations (c.163+1G>T, c.164-2A>G, c.461A>T [p.Y154F], and c.510-1G>A) and a novel polymorphism (c.60+62C>T) were also identified. A number of patients have been previously tested for their response to dietary supplementation of tetrahydrobiopterin (BH4), the cofactor of PAH. Correlation between genotype and the responses revealed that although genotype is a major determinant of BH4 responsiveness, patients with the same genotype may also show disparate responses to this treatment. A clinical and biochemical evaluation should be undertaken to determine the effectiveness of PKU treatment by supplementation of BH4.

Assessment and management of nutrition and growth in Rett syndrome

OBJECTIVES

We developed recommendations for the clinical management of poor growth and weight gain in Rett syndrome through evidence review and the consensus of an expert panel of clinicians.

METHODS

Initial draft recommendations were created based upon literature review and 34 open-ended questions in which the literature was lacking. Statements and questions were made available to an international, multidisciplinary panel of clinicians in an online format and a Microsoft Word-formatted version of the draft via e-mail. Input was sought using a 2-stage modified Delphi process to reach consensus. Items included clinical assessment of growth, anthropometry, feeding difficulties and management to increase energy intake, decrease feeding difficulties, and consideration of gastrostomy.

RESULTS

Agreement was achieved on 101 of 112 statements. A comprehensive approach to the management of poor growth in Rett syndrome is recommended that takes into account factors such as feeding difficulties and nutritional needs. A body mass index of approximately the 25th centile can be considered as a reasonable target in clinical practice. Gastrostomy is indicated for extremely poor growth, if there is risk of aspiration and if feeding times are prolonged.

CONCLUSIONS

These evidence- and consensus-based recommendations have the potential to improve care of nutrition and growth in a rare condition and stimulate research to improve the present limited evidence base.

Update on the investigation of children with delayed development

Children develop in the domains of cognition, speech and language, motor, personal skills, social skills and activities of daily living in a predictable and organised manner. Between 3000 and 9000 Australian children born in any one year may be diagnosed with global developmental delay. Paediatricians are often faced with the dilemma of 'who' and 'how' to investigate, as the yield is often considered to be low. 'Best practice' guidelines on the investigation of global developmental delay have been published, but the evidence available for the specific recommendations varies significantly and is based mostly on levels III and IV evidence (non-experimental descriptive studies and expert opinions). This paper discusses the current views and suggests a possible algorithm for clinical practice in Australia.

Altered attainment of developmental milestones influences the age of diagnosis of rett syndrome

The early developmental history prior to the manifestation of Rett syndrome features is of clinical interest. This study describes the attainment of gross developmental milestones and regression, and assesses the relationships between genotype and age at diagnosis. The Australian Rett Syndrome Database and International Rett Syndrome Phenotype Database were used to source a total of 293 confirmed female subjects. Most girls learned to sit, were able to babble or use words, and approximately half learned to walk. Altered milestone attainment was associated with earlier diagnosis. There was variation in the acquisition of milestones, the age of regression, and the age of diagnosis by genotype. Most parents expressed concerns about unusual behaviors or development during infancy, and a more subtle atypical development during infancy was reported for most girls. It is important for clinicians to be aware of variable early development in Rett syndrome and that timely genetic testing is not precluded on this account.