Jose E. Abdenur

Molecular and clinical genetics of mitochondrial diseases due to POLG mutations.

Mutations in the POLG gene have emerged as one of the most common causes of inherited mitochondrial disease in children and adults. They are responsible for a heterogeneous group of at least 6 major phenotypes of neurodegenerative disease that include: 1) childhood Myocerebrohepatopathy Spectrum disorders (MCHS), 2) Alpers syndrome, 3) Ataxia Neuropathy Spectrum (ANS) disorders, 4) Myoclonus Epilepsy Myopathy Sensory Ataxia (MEMSA), 5) autosomal recessive Progressive External Ophthalmoplegia (arPEO), and 6) autosomal dominant Progressive External Ophthalmoplegia (adPEO). Due to the clinical heterogeneity, time‐dependent evolution of symptoms, overlapping phenotypes, and inconsistencies in muscle pathology findings, definitive diagnosis relies on the molecular finding of deleterious mutations. We sequenced the exons and flanking intron region from approximately 350 patients displaying a phenotype consistent with POLG related mitochondrial disease and found informative mutations in 61 (17%). Two mutant alleles were identified in 31 unrelated index patients with autosomal recessive POLG‐related disorders. Among them, 20 (67%) had Alpers syndrome, 4 (13%) had arPEO, and 3 (10%) had ANS. In addition, 30 patients carrying one altered POLG allele were found. A total of 25 novel alterations were identified, including 6 null mutations. We describe the predicted structural/functional and clinical importance of the previously unreported missense variants and discuss their likelihood of being pathogenic. In conclusion, sequence analysis allows the identification of mutations responsible for POLG‐related disorders and, in most of the autosomal recessive cases where two mutant alleles are found in trans, finding deleterious mutations can provide an unequivocal diagnosis of the disease. Published 2008 Wiley‐Liss, Inc.

Mutations in GDP-Mannose Pyrophosphorylase B Cause Congenital and Limb-Girdle Muscular Dystrophies Associated with Hypoglycosylation of α-Dystroglycan

Congenital muscular dystrophies with hypoglycosylation of α-dystroglycan (α-DG) are a heterogeneous group of disorders often associated with brain and eye defects in addition to muscular dystrophy. Causative variants in 14 genes thought to be involved in the glycosylation of α-DG have been identified thus far. Allelic mutations in these genes might also cause milder limb-girdle muscular dystrophy phenotypes. Using a combination of exome and Sanger sequencing in eight unrelated individuals, we present evidence that mutations in guanosine diphosphate mannose (GDP-mannose) pyrophosphorylase B (GMPPB) can result in muscular dystrophy variants with hypoglycosylated α-DG. GMPPB catalyzes the formation of GDP-mannose from GTP and mannose-1-phosphate. GDP-mannose is required for O-mannosylation of proteins, including α-DG, and it is the substrate of cytosolic mannosyltransferases. We found reduced α-DG glycosylation in the muscle biopsies of affected individuals and in available fibroblasts. Overexpression of wild-type GMPPB in fibroblasts from an affected individual partially restored glycosylation of α-DG. Whereas wild-type GMPPB localized to the cytoplasm, five of the identified missense mutations caused formation of aggregates in the cytoplasm or near membrane protrusions. Additionally, knockdown of the GMPPB ortholog in zebrafish caused structural muscle defects with decreased motility, eye abnormalities, and reduced glycosylation of α-DG. Together, these data indicate that GMPPB mutations are responsible for congenital and limb-girdle muscular dystrophies with hypoglycosylation of α-DG.

Initial experience in the treatment of inherited mitochondrial disease with EPI-743.

Inherited mitochondrial respiratory chain disorders are progressive, life-threatening conditions for which there are limited supportive treatment options and no approved drugs. Because of this unmet medical need, as well as the implication of mitochondrial dysfunction as a contributor to more common age-related and neurodegenerative disorders, mitochondrial diseases represent an important therapeutic target. Thirteen children and one adult with genetically-confirmed mitochondrial disease (polymerase γ deficiency, n=4; Leigh syndrome, n=4; MELAS, n=3; mtDNA deletion syndrome, n=2; Friedreich ataxia, n=1) at risk for progressing to end-of-life care within 90 days were treated with EPI-743, a novel para-benzoquinone therapeutic, in a subject controlled, open-label study. Serial measures of safety and efficacy were obtained that included biochemical, neurological, quality-of-life, and brain redox assessments using technetium-99m-hexamethylpropyleneamine oxime (HMPAO) single photon emission computed tomography (SPECT) radionuclide imaging. Twelve patients treated with EPI-743 have survived; one polymerase γ deficiency patient died after developing pneumonia and one patient with Surf-1 deficiency died after completion of the protocol. Of the 12 survivors, 11 demonstrated clinical improvement, with 3 showing partial relapse, and 10 of the survivors also had an improvement in quality-of-life scores at the end of the 13-week emergency treatment protocol. HMPAO SPECT scans correlated with clinical response; increased regional and whole brain HMPAO uptake was noted in the clinical responders and the one subject who did not respond clinically had decreased regional and whole brain HMPAO uptake. EPI-743 has modified disease progression in >90% of patients in this open-label study as assessed by clinical, quality-of-life, and non-invasive brain imaging parameters. Data obtained herein suggest that EPI-743 may represent a new drug for the treatment of inherited mitochondrial respiratory chain disorders. Prospective controlled trials will be undertaken to substantiate these initial promising observations. Furthermore, HMPAO SPECT imaging may be a valuable tool for the detection of central nervous system redox defects and for monitoring response to treatments directed at modulating abnormal redox.

Clinical and biochemical features of aromatic L-amino acid decarboxylase deficiency

Objective: To describe the current treatment; clinical, biochemical, and molecular findings; and clinical follow-up of patients with aromatic l-amino acid decarboxylase (AADC) deficiency. Method: Clinical and biochemical data of 78 patients with AADC deficiency were tabulated in a database of pediatric neurotransmitter disorders (JAKE). A total of 46 patients have been previously reported; 32 patients are described for the first time. Results: In 96% of AADC-deficient patients, symptoms (hypotonia 95%, oculogyric crises 86%, and developmental retardation 63%) became clinically evident during infancy or childhood. Laboratory diagnosis is based on typical CSF markers (low homovanillic acid, 5-hydroxyindoleacidic acid, and 3-methoxy-4-hydroxyphenolglycole, and elevated 3-O-methyl-l-dopa, l-dopa, and 5-hydroxytryptophan), absent plasma AADC activity, or elevated urinary vanillactic acid. A total of 24 mutations in the DDC gene were detected in 49 patients (8 reported for the first time: p.L38P, p.Y79C, p.A110Q, p.G123R, p.I42fs, c.876G>A, p.R412W, p.I433fs) with IVS6+ 4A>T being the most common one (allele frequency 45%). Conclusion: Based on clinical symptoms, CSF neurotransmitters profile is highly indicative for the diagnosis of aromatic l-amino acid decarboxylase deficiency. Treatment options are limited, in many cases not beneficial, and prognosis is uncertain. Only 15 patients with a relatively mild form clearly improved on a combined therapy with pyridoxine (B6)/pyridoxal phosphate, dopamine agonists, and monoamine oxidase B inhibitors.

Sepiapterin reductase deficiency: A Treatable Mimic of Cerebral Palsy

Sepiapterin reductase deficiency (SRD) is an under‐recognized levodopa‐responsive disorder. We describe clinical, biochemical, and molecular findings in a cohort of patients with this treatable condition. We aim to improve awareness of the phenotype and available diagnostic and therapeutic strategies to reduce delayed diagnosis or misdiagnosis, optimize management, and improve understanding of pathophysiologic mechanisms.

Diagnosis of isovaleric acidaemia by tandem mass spectrometry: False positive result due to pivaloylcarnitine in a newborn screening programme

Tandem mass spectrometric analysis of acylcarnitines and amino acids has been applied in newborn screening programmes for the detection of several inborn errors of metabolism. We report a false positive result for isovaleric acidaemia in a newborn screening programme using this method. The newborn screening sample showed a very prominent signal corresponding to the mass of isovalerylcarnitine. Repeat samples (age 6 days) of blood and urine showed similar results. However, urine organic acids were normal. Acylcarnitine analysis in blood, breast milk and urine of the mother also showed a prominent signal of the same mass. Gas chromatography–mass spectrometry of the methyl esters demonstrated that the signal in the patients urine was due to the presence of pivaloylcarnitine, which is isomeric with isovalerylcarnitine. The patients mother was receiving an antibiotic containing a derivative of pivalic acid to treat a urinary tract infection. Follow-up samples in the patient and the mother confirmed a decrease in the levels of pivaloylcarnitine, concomitant with the discontinuation of the treatment.We conclude that pivaloylcarnitine can give a false positive result for isovaleric acidaemia in newborns whose mothers are on treatment with pivoxilsulbactam-containing antibiotics.

Safety and efficacy of enzyme replacement therapy in combination with hematopoietic stem cell transplantation in Hurler syndrome

Purpose: Hurler syndrome is a debilitating genetic disease with a typical life span of 5 to 8 years. Early hematopoietic stem cell transplantation (HSCT) mitigates disease symptoms and improves survival. However, morbidity and mortality associated with HSCT can limit its success. We describe the initial experience with combined use of enzyme replacement therapy (ERT, laronidase) and HSCT in Hurler syndrome.Methods: Thirteen transplants were performed in 12 patients. ERT was given at a standard dose of 0.58 mg/kg per week. Transplant conditioning regimen and donor graft source were determined by institutional protocol.Results: The median age at initiation of ERT was 12 months (range, 8 to 18 months). The median duration of pre-HSCT ERT was 12 weeks (range, 4 to 28). All but 1 patient tested showed decrease in urinary GAG excretion during ERT. ERT infusion-related toxicity was limited to mild reactions. Development of antibodies to laronidase did not correlate with infusion reactions or responses in urinary GAG excretion. ERT was given for a median of 7 weeks (range, 3 to 20) after HSCT. After transplantation, eight patients demonstrated complete donor engraftment and four suffered graft failure. Two patients required ventilator support and three developed acute GVHD. Eleven of the 12 patients are surviving with a median follow-up of 3 months (range, 1 to 7 months).Conclusions: In children with Hurler syndrome, ERT with HSCT is feasible and well tolerated. Development of antibodies against exogenous enzyme does not appear to correlate with infusion reactions or response to ERT. A prospective study is needed to determine the effect of concomitant ERT on transplant outcomes.

Diagnosis and management of glycogen storage disease type I: a practice guideline of the American College of Medical Genetics and Genomics.

Disclaimer: This guideline is designed primarily as an educational resource for clinicians to help them provide quality medical services. Adherence to this guideline is completely voluntary and does not necessarily ensure a successful medical outcome. This guideline should not be considered inclusive of all proper procedures and tests or exclusive of other procedures and tests that are reasonably directed toward obtaining the same results. In determining the propriety of any specific procedure or test, the clinician should apply his or her own professional judgment to the specific clinical circumstances presented by the individual patient or specimen. Clinicians are encouraged to document the reasons for the use of a particular procedure or test, whether or not it is in conformance with this guideline. Clinicians also are advised to take notice of the date this guideline was adopted and to consider other medical and scientific information that becomes available after that date. It also would be prudent to consider whether intellectual property interests may restrict the performance of certain tests and other procedures.Purpose:Glycogen storage disease type I (GSD I) is a rare disease of variable clinical severity that primarily affects the liver and kidney. It is caused by deficient activity of the glucose 6-phosphatase enzyme (GSD Ia) or a deficiency in the microsomal transport proteins for glucose 6-phosphate (GSD Ib), resulting in excessive accumulation of glycogen and fat in the liver, kidney, and intestinal mucosa. Patients with GSD I have a wide spectrum of clinical manifestations, including hepatomegaly, hypoglycemia, lactic acidemia, hyperlipidemia, hyperuricemia, and growth retardation. Individuals with GSD type Ia typically have symptoms related to hypoglycemia in infancy when the interval between feedings is extended to 3–4 hours. Other manifestations of the disease vary in age of onset, rate of disease progression, and severity. In addition, patients with type Ib have neutropenia, impaired neutrophil function, and inflammatory bowel disease. This guideline for the management of GSD I was developed as an educational resource for health-care providers to facilitate prompt, accurate diagnosis and appropriate management of patients.Methods:A national group of experts in various aspects of GSD I met to review the evidence base from the scientific literature and provided their expert opinions. Consensus was developed in each area of diagnosis, treatment, and management.Results:This management guideline specifically addresses evaluation and diagnosis across multiple organ systems (hepatic, kidney, gastrointestinal/nutrition, hematologic, cardiovascular, reproductive) involved in GSD I. Conditions to consider in the differential diagnosis stemming from presenting features and diagnostic algorithms are discussed. Aspects of diagnostic evaluation and nutritional and medical management, including care coordination, genetic counseling, hepatic and renal transplantation, and prenatal diagnosis, are also addressed.Conclusion:A guideline that facilitates accurate diagnosis and optimal management of patients with GSD I was developed. This guideline helps health-care providers recognize patients with all forms of GSD I, expedite diagnosis, and minimize adverse sequelae from delayed diagnosis and inappropriate management. It also helps to identify gaps in scientific knowledge that exist today and suggests future studies.Genet Med 16 11.

A Homozygous Mutation in KCTD7 Links Neuronal Ceroid Lipofuscinosis to the Ubiquitin-Proteasome System

Neuronal ceroid lipofuscinosis (NCL) is a genetically heterogeneous group of lysosomal diseases that collectively compose the most common Mendelian form of childhood-onset neurodegeneration. It is estimated that ∼8% of individuals diagnosed with NCL by conservative clinical and histopathologic criteria have been ruled out for mutations in the nine known NCL-associated genes, suggesting that additional genes remain unidentified. To further understand the genetic underpinnings of the NCLs, we performed whole-exome sequencing on DNA samples from a Mexican family affected by a molecularly undefined form of NCL characterized by infantile-onset progressive myoclonic epilepsy (PME), vision loss, cognitive and motor regression, premature death, and prominent NCL-type storage material. Using a recessive model to filter the identified variants, we found a single homozygous variant, c.550C>T in KCTD7, that causes a p.Arg184Cys missense change in potassium channel tetramerization domain-containing protein 7 (KCTD7) in the affected individuals. The mutation was predicted to be deleterious and was absent in over 6,000 controls. The identified variant altered the localization pattern of KCTD7 and abrogated interaction with cullin-3, a ubiquitin-ligase component and known KCTD7 interactor. Intriguingly, murine cerebellar cells derived from a juvenile NCL model (CLN3) showed enrichment of endogenous KCTD7. Whereas KCTD7 mutations have previously been linked to PME without lysosomal storage, this study clearly demonstrates that KCTD7 mutations also cause a rare, infantile-onset NCL subtype designated as CLN14.

Expanded clinical and molecular spectrum of guanidinoacetate methyltransferase (GAMT) deficiency.

Guanidinoacetate methyltransferase (GAMT) deficiency is a disorder of creatine biosynthesis, characterized by excessive amounts of guanidinoacetate in body fluids, deficiency of creatine in the brain, and presence of mutations in the GAMT gene. We present here 8 new patients with GAMT deficiency along with their clinical, biochemical and molecular data. The age at diagnosis of our patients ranges from 0 to 14 years. The age of onset of seizures usually ranges from infancy to 3 years. However, one of our patients developed seizures at age 5; progressing to myoclonic epilepsy at age 8 years and another patient has not developed seizures at age 17 years. Five novel mutations were identified: c.37ins26 (p.G13PfsX38), c.403G>T (p.D135Y), c.507_521dup15 (p.C169_S173dup), c.402C>G (p.Y134X) and c.610_611delAGinsGAA (p.R204EfsX63). Six patients had the c.327G>A (last nucleotide of exon 2) splice-site mutation which suggests that this is one of the most common mutations in the GAMT gene, second only to the known Portuguese founder mutation, c.59G>C (p.W20S). Our data suggests that the clinical presentation can be variable and the diagnosis may be overlooked due to unawareness of this disorder. Therefore, GAMT deficiency should be considered in the differential diagnosis of progressive myoclonic epilepsy as well as in unexplained developmental delay or regression with dystonia, even if the patient has no history of seizures. As more patients are reported, the prevalence of GAMT deficiency will become known and guidelines for prenatal diagnosis, newborn screening, presymptomatic testing and treatment, will need to be formulated.