Mitochondrial respiratory chain dysfunction in a patient with a heterozygous de novo CTBP1 variant.

The C-terminal binding protein 1 (CTBP1) functions as a transcriptional corepressor in vertebrates and has been identified to have critical roles in nervous system growth and development. Pathogenic variants in the CTBP1 gene has been shown to cause hypotonia, ataxia, developmental delay and tooth enamel defect syndrome (HADDTS). There have only been 16 cases reported to date with heterozygous, pathogenic variants in CTBP1 manifesting with a neurodevelopmental phenotype. We report a further case of a pathogenic, heterozygous, de novo variant in CTBP1 identified by whole exome sequencing in a female with the typical phenotype of global developmental delay, hypotonia, cerebellar dysfunction and failure to thrive. Additionally, muscle biopsy demonstrates evidence of a respiratory chain defect, only previously reported once in the literature. This supports the role of CTBP1 in maintenance of normal mitochondrial activity and highlights the importance of considering secondary mitochondrial dysfunction in genes not directly involved in the mitochondrial respiratory chain.

Standardized practices for RNA diagnostics using clinically accessible specimens reclassifies 75% of putative splicing variants.

PURPOSE: Genetic variants causing aberrant premessenger RNA splicing are increasingly being recognized as causal variants in genetic disorders. In this study, we devise standardized practices for polymerase chain reaction (PCR)-based RNA diagnostics using clinically accessible specimens (blood, fibroblasts, urothelia, biopsy). METHODS: A total of 74 families with diverse monogenic conditions (31% prenatal-congenital onset, 47% early childhood, and 22% teenage-adult onset) were triaged into PCR-based RNA testing, with comparative RNA sequencing for 19 cases. RESULTS: Informative RNA assay data were obtained for 96% of cases, enabling variant reclassification for 75% variants that can be used for genetic counseling (71%), to inform clinical care (32%) and prenatal counseling (41%). Variant-associated mis-splicing was highly reproducible for 28 cases with samples from ≥2 affected individuals or heterozygotes and 10 cases with ≥2 biospecimens. PCR amplicons encompassing another segregated heterozygous variant was vital for clinical interpretation of 22 of 79 variants to phase RNA splicing events and discern complete from partial mis-splicing. CONCLUSION: RNA diagnostics enabled provision of a genetic diagnosis for 64% of recruited cases. PCR-based RNA diagnostics has capacity to analyze 81.3% of clinically significant genes, with long amplicons providing an advantage over RNA sequencing to phase RNA splicing events. The Australasian Consortium for RNA Diagnostics (SpliceACORD) provide clinically-endorsed, standardized protocols and recommendations for interpreting RNA assay data.

Safety and Efficacy of Elosulfase Alfa in Australian Patients with Morquio a Syndrome: A Phase 3b Study

Abstract The safety and efficacy of elosulfase alfa were evaluated in a multicenter, open-label, phase 3b study in Australian Morquio A patients, consisting of a 49-week initial phase and an extension phase until elosulfase alfa was government funded. Thirteen patients (1-27 years) were enrolled. No new safety concerns were identified over 138 weeks. Most drug-related adverse events were mild or moderate in severity; none led to study discontinuation. After 49 weeks of treatment, median improvements from baseline were seen in the 6-minute walk test (+41.0 m), 3-minute stair climb test (+14.0 stairs/min), forced vital capacity (+16.4%), forced expiratory volume in 1 second (+14.1%), urine keratan sulfate (-7.1 µg/mg creatinine), and pain intensity. Growth, cardiac function, sleep, and quality of life results were mixed or stable. These results provide further evidence of the acceptable safety/tolerability profile of elosulfase alfa. The improvements in endurance, pulmonary function, and pain support findings from previous studies.

Structured Dietary Management Dramatically Improves Marked Transaminitis, Metabolic and Clinical Profiles in Glycogen Storage Disease Type IXa

Abstract Glycogen storage disease type IXa (GSD IXa) presents in childhood with hepatomegaly, poor growth, and ketotic hypoglycemia. Clinical course is usually mild, often not requiring treatment with attenuation of symptoms with increasing age. The phenotypic spectrum has recently expanded to include more severe involvement with hepatic fibrosis or cirrhosis warranting dietary therapy. We report a 2-year-old boy with a severe phenotype of GSD IXa presenting with a massive hepatomegaly, significant transaminitis, recurrent ketotic hypoglycemia, and short stature. Aggressive dietary management with regular feeds, frequent uncooked cornstarch doses, and protein supplementation resulted in clinical improvements including enhanced growth velocity, energy levels, overall well-being, and reduction in hepatomegaly with restitutions in biochemical parameters. We concur with a recent report which proposed that GSD IXa is not always a mild condition but instead part of an expanding phenotypic spectrum warranting intensive dietary management to optimize metabolic control and quality of life.

Monitoring of Therapy for Mucopolysaccharidosis Type I Using Dysmorphometric Facial Phenotypic Signatures.

There is a pattern of progressive facial dysmorphology in mucopolysaccharidosis type I (MPS I). Advances in 3D facial imaging have facilitated the development of tools, including dysmorphometrics, to objectively and precisely detect these facial phenotypes. Therefore, we investigated the application of dysmorphometrics as a noninvasive therapy-monitoring tool, by longitudinally scoring facial dysmorphology in a child with MPS I receiving enzyme replacement therapy (ERT) and bone marrow transplantation (BMT). Both dysmorphometric measures showed a decreasing trend, and the greatest differences were found in the severity of facial discordance (Z-RMSE), displaying scores >3 SD higher than the mean at their peak, in comparison to Z-RSD scores that mostly fell within the normative range (maximum; 1.5 SD from the mean). In addition to the general trend of reduced facial dysmorphology with treatment, initial fluctuations were also evident that may have related to transient subcutaneous facial fluctuations, in the context of conditioning for bone marrow transplant. These findings support the potential of our approach as a sensitive, noninvasive, and rapid means of assessing treatment response or failure in clinical trials, and for established therapies, and would be applicable for other inherited disorders of metabolism.

Overcoming the barriers to diagnosis of Morquio A syndrome.

BACKGROUND: Morquio A syndrome is an autosomal recessive lysosomal storage disease often resulting in life-threatening complications. Early recognition and proficient diagnosis is imperative to facilitate prompt treatment and prevention of clinical complications. METHODS: Experts in Asia Pacific reviewed medical records focusing on presenting signs and symptoms leading to a diagnosis of Morquio A syndrome. RESULTS: Eighteen patients (77% female) had a mean (median; min, max) age of 77.1 (42.0; 0.0, 540.0) months at symptom onset, 78.9 (42.0; 4.5, 540.0) months at presentation and 113.8 (60.0; 7.0, 540.0) months at diagnosis. Orthopedic surgeons and pediatricians were most frequently consulted pre-diagnosis while clinical geneticists/metabolic specialists most frequently made the diagnosis. Delayed diagnoses were due to atypical symptoms for 5 patients (28%), while 4 patients (22%) experienced each of subtle symptoms, symptoms commonly associated with other diseases, or false-negative urine glycosaminoglycan analysis. Two patients (11%) each experienced overgrowth within the first year of life. Two patients with Morquio A syndrome (11%) were diagnosed with craniosynostosis and 1 (6%) for each of Legg-Calvé-Perthes disease, Leri-Weill syndrome, and pseudoachondroplasia. Early radiographic features of Morquio A syndrome led to more efficient diagnosis. CONCLUSIONS: Increased awareness of clinical symptomology overlapping with Morquio A syndrome is essential. Clinicians encountering patients with certain skeletal dysplasia should consider Morquio A syndrome in their differential diagnosis. Atypical or subtle symptoms should not eliminate Morquio A syndrome from the differential diagnosis, especially for patients who may have non-classical phenotype of Morquio A syndrome.

Inborn errors of pyrimidine metabolism: clinical update and therapy.

Inborn errors involving enzymes essential for pyrimidine nucleotide metabolism have provided new insights into their fundamental physiological roles as vital constituents of nucleic acids as well as substrates of lipid and carbohydrate metabolism and in oxidative phosphorylation. Genetic aberrations of pyrimidine pathways lead to diverse clinical manifestations including neurological, immunological, haematological, renal impairments, adverse reactions to analogue therapy and association with malignancies. Maintenance of cellular nucleotides depends on the three aspects of metabolism of pyrimidines: de novo synthesis, catabolism and recycling of these metabolites. Of the ten recognised disorders of pyrimidine metabolism treatment is currently restricted to only two disorders: hereditary orotic aciduria (oral uridine therapy) and mitochondrial neurogastrointestinal encephalomyopathy (MNGIE; allogeneic hematopoetic stem cell transplant and enzyme replacement). The ubiquitous role that pyrimidine metabolism plays in human life highlights the importance of improving diagnostic evaluation in suggestive clinical settings, which will contribute to the elucidation of new defects, future development of novel drugs and therapeutic strategies. Limited awareness of the expanding phenotypic spectrum, with relatively recent descriptions of newer disorders, compounded by considerable genetic heterogeneity has often contributed to the delays in the diagnosis of this group of disorders. The lack of an easily recognisable, easily measurable end product, akin to uric acid in purine metabolism, has contributed to the under-recognition of these disorders.This review describes the currently known inborn errors of pyrimidine metabolism, their variable phenotypic presentations, established diagnostic methodology and recognised treatment options.

Inborn errors of purine metabolism: clinical update and therapies.

Inborn errors of purine metabolism exhibit broad neurological, immunological, haematological and renal manifestations. Limited awareness of the phenotypic spectrum, the recent descriptions of newer disorders and considerable genetic heterogeneity, have contributed to long diagnostic odysseys for affected individuals. These enzymes are widely but not ubiquitously distributed in human tissues and are crucial for synthesis of essential nucleotides, such as ATP, which form the basis of DNA and RNA, oxidative phosphorylation, signal transduction and a range of molecular synthetic processes. Depletion of nucleotides or accumulation of toxic intermediates contributes to the pathogenesis of these disorders. Maintenance of cellular nucleotides depends on the three aspects of metabolism of purines (and related pyrimidines): de novo synthesis, catabolism and recycling of these metabolites. At present, treatments for the clinically significant defects of the purine pathway are restricted: purine 5'-nucleotidase deficiency with uridine; familial juvenile hyperuricaemic nephropathy (FJHN), adenine phosphoribosyl transferase (APRT) deficiency, hypoxanthine phosphoribosyl transferase (HPRT) deficiency and phosphoribosyl-pyrophosphate synthetase superactivity (PRPS) with allopurinol; adenosine deaminase (ADA) and purine nucleoside phosphorylase (PNP) deficiencies have been treated by bone marrow transplantation (BMT), and ADA deficiency with enzyme replacement with polyethylene glycol (PEG)-ADA, or erythrocyte-encapsulated ADA; myeloadenylate deaminase (MADA) and adenylosuccinate lyase (ADSL) deficiencies have had trials of oral ribose; PRPS, HPRT and adenosine kinase (ADK) deficiencies with S-adenosylmethionine; and molybdenum cofactor deficiency of complementation group A (MOCODA) with cyclic pyranopterin monophosphate (cPMP). In this review we describe the known inborn errors of purine metabolism, their phenotypic presentations, established diagnostic methodology and recognised treatment options.

Treatment of Lesch-Nyhan disease with S-adenosylmethionine: experience with five young Malaysians, including a girl.

BACKGROUND: Lesch-Nyhan disease (LND) is a rare X-linked recessive neurogenetic disorder caused by deficiency of the purine salvage enzyme hypoxanthine phosphoribosyltransferase (HPRT, EC 2.4.2.8) which is responsible for recycling purine bases into purine nucleotides. Affected individuals have hyperuricemia leading to gout and urolithiasis, accompanied by a characteristic severe neurobehavioural phenotype with compulsive self-mutilation, extrapyramidal motor disturbances and cognitive impairment. AIM: For its theoretical therapeutic potential to replenish the brain purine nucleotide pool, oral supplementation with S-adenosylmethionine (SAMe) was trialed in 5 Malaysian children with LND, comprising 4 related Malay children from 2 families, including an LND girl, and a Chinese Malaysian boy. RESULTS: Dramatic reductions of self-injury and aggressive behaviour, as well as a milder reduction of dystonia, were observed in all 5 patients. Other LND neurological symptoms did not improve during SAMe therapy. DISCUSSION: Molecular mechanisms proposed for LND neuropathology include GTP depletion in the brain leading to impaired dopamine synthesis, dysfunction of G-protein-mediated signal transduction, and defective developmental programming of dopamine neurons. The improvement of our LND patients on SAMe, particularly the hallmark self-injurious behaviour, echoed clinical progress reported with another purine nucleotide depletion disorder, Arts Syndrome, but contrasted lack of benefit with the purine disorder adenylosuccinate lyase deficiency. This first report of a trial of SAMe therapy in LND children showed remarkably encouraging results that warrant larger studies.

Adenosine kinase deficiency disrupts the methionine cycle and causes hypermethioninemia, encephalopathy, and abnormal liver function.

Four inborn errors of metabolism (IEMs) are known to cause hypermethioninemia by directly interfering with the methionine cycle. Hypermethioninemia is occasionally discovered incidentally, but it is often disregarded as an unspecific finding, particularly if liver disease is involved. In many individuals the hypermethioninemia resolves without further deterioration, but it can also represent an early sign of a severe, progressive neurodevelopmental disorder. Further investigation of unclear hypermethioninemia is therefore important. We studied two siblings affected by severe developmental delay and liver dysfunction. Biochemical analysis revealed increased plasma levels of methionine, S-adenosylmethionine (AdoMet), and S-adenosylhomocysteine (AdoHcy) but normal or mildly elevated homocysteine (Hcy) levels, indicating a block in the methionine cycle. We excluded S-adenosylhomocysteine hydrolase (SAHH) deficiency, which causes a similar biochemical phenotype, by using genetic and biochemical techniques and hypothesized that there was a functional block in the SAHH enzyme as a result of a recessive mutation in a different gene. Using exome sequencing, we identified a homozygous c.902C>A (p.Ala301Glu) missense mutation in the adenosine kinase gene (ADK), the function of which fits perfectly with this hypothesis. Increased urinary adenosine excretion confirmed ADK deficiency in the siblings. Four additional individuals from two unrelated families with a similar presentation were identified and shown to have a homozygous c.653A>C (p.Asp218Ala) and c.38G>A (p.Gly13Glu) mutation, respectively, in the same gene. All three missense mutations were deleterious, as shown by activity measurements on recombinant enzymes. ADK deficiency is a previously undescribed, severe IEM shedding light on a functional link between the methionine cycle and adenosine metabolism.