Luc Régal

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.

Mutations in GTPBP3 Cause a Mitochondrial Translation Defect Associated with Hypertrophic Cardiomyopathy, Lactic Acidosis, and Encephalopathy

Respiratory chain deficiencies exhibit a wide variety of clinical phenotypes resulting from defective mitochondrial energy production through oxidative phosphorylation. These defects can be caused by either mutations in the mtDNA or mutations in nuclear genes coding for mitochondrial proteins. The underlying pathomechanisms can affect numerous pathways involved in mitochondrial physiology. By whole-exome and candidate gene sequencing, we identified 11 individuals from 9 families carrying compound heterozygous or homozygous mutations in GTPBP3, encoding the mitochondrial GTP-binding protein 3. Affected individuals from eight out of nine families presented with combined respiratory chain complex deficiencies in skeletal muscle. Mutations in GTPBP3 are associated with a severe mitochondrial translation defect, consistent with the predicted function of the protein in catalyzing the formation of 5-taurinomethyluridine (τm(5)U) in the anticodon wobble position of five mitochondrial tRNAs. All case subjects presented with lactic acidosis and nine developed hypertrophic cardiomyopathy. In contrast to individuals with mutations in MTO1, the protein product of which is predicted to participate in the generation of the same modification, most individuals with GTPBP3 mutations developed neurological symptoms and MRI involvement of thalamus, putamen, and brainstem resembling Leigh syndrome. Our study of a mitochondrial translation disorder points toward the importance of posttranscriptional modification of mitochondrial tRNAs for proper mitochondrial function.

TUBA1A mutations From isolated lissencephaly to familial polymicrogyria

Background: Mutations in the TUBA1A gene have been reported in patients with lissencephaly and perisylvian pachygyria. Methods: Twenty-five patients with malformations of cortical development ranging from lissencephaly to polymicrogyria were screened for mutations in TUBA1A. Results: Two novel heterozygous missense mutations in TUBA1A were identified: c.629A>G (p.Tyr210Cys) occurring de novo in a boy with lissencephaly, and c.13A>C (p.Ile5Leu) affecting 2 sisters with polymicrogyria whose mother presented somatic mosaicism for the mutation. Conclusions: Mutations in TUBA1A have been described in patients with lissencephaly and pachygyria. We report a mutation in TUBA1A as a cause of polymicrogyria. So far, all mutations in TUBA1A have occurred de novo, resulting in isolated cases. This article describes familial recurrence of TUBA1A mutations due to somatic mosaicism in a parent. These findings broaden the phenotypic spectrum associated with TUBA1A mutations and have implications for genetic counseling.

RFT1-CDG: Deafness as a novel feature of congenital disorders of glycosylation

SummaryCongenital disorders of glycosylation (CDG) are genetic diseases due to defects in the synthesis of glycans and in the attachment of glycans to lipids and proteins. Actually, some 42 CDG are known including defects in protein N-glycosylation, in protein O-glycosylation, in lipid glycosylation, and in multiple and other glycosylation pathways. Most CDG are multisystem diseases and a large number of signs and symptoms have already been reported in CDG. An exception to this is deafness. This symptom has not been observed as a consistent feature in CDG. In 2008, a novel defect was identified in protein N-glycosylation, namely in RFT1. This is a defect in the assembly of N-glycans. RFT1 is involved in the transfer of Man5GlcNAc2-PP-Dol from the cytoplasmic to the luminal side of the endoplasmic reticulum. According to the novel nomenclature (non-italicized gene symbol followed by -CDG) this defect is named RFT1-CDG. Recently, three other patients with RFT1-CDG have been reported and here we report two novel patients. Remarkably, all six patients with RFT1-CDG show sensorineural deafness as part of a severe neurological syndrome. We conclude that RFT1-CDG is the first ‘deafness-CDG’. CDG should be included in the work-up of congenital, particularly syndromic, hearing loss.

PREPL deficiency with or without cystinuria causes a novel myasthenic syndrome

Objective: To investigate the genetic and physiologic basis of the neuromuscular symptoms of hypotonia-cystinuria syndrome (HCS) and isolated PREPL deficiency, and their response to therapy. Methods: We performed molecular genetic, histochemical, immunoblot, and ultrastructural studies, investigated neuromuscular transmission in vitro in a patient with isolated PREPL deficiency, and evaluated the effect of pyridostigmine in this patient and in 3 patients with the HCS. Results: HCS is caused by recessive deletions involving the SLC3A1 and PREPL genes. The major clinical features of HCS are type A cystinuria, growth hormone deficiency, muscle weakness, ptosis, and feeding problems. The proband with isolated PREPL deficiency had myasthenic symptoms since birth and a positive edrophonium test but no cystinuria. She and 1 of 3 patients with HCS responded transiently to pyridostigmine during infancy. The proband harbors a paternally inherited nonsense mutation in PREPL and a maternally inherited deletion involving both PREPL and SLC3A1; therefore, the PREPL deficiency determines the phenotype. We detected no PREPL expression in the patients muscle and endplates. Electrophysiology studies revealed decreased quantal content of the endplate potential and reduced amplitude of the miniature endplate potential without endplate acetylcholine receptor deficiency or altered endplate geometry. Conclusion: Isolated PREPL deficiency is a novel monogenic disorder that causes a congenital myasthenic syndrome with pre- and postsynaptic features and growth hormone deficiency. The myasthenic symptoms in PREPL deficiency with or without cystinuria may respond to pyridostigmine in early life. We attribute the myasthenia to abrogated interaction of PREPL with adaptor protein 1.

COG5-CDG: expanding the clinical spectrum

BackgroundThe Conserved Oligomeric Golgi (COG) complex is involved in the retrograde trafficking of Golgi components, thereby affecting the localization of Golgi glycosyltransferases. Deficiency of a COG-subunit leads to defective protein glycosylation, and thus Congenital Disorders of Glycosylation (CDG). Mutations in subunits 1, 4, 5, 6, 7 and 8 have been associated with CDG-II. The first patient with COG5-CDG was recently described (Paesold-Burda et al. Hum Mol Genet 2009; 18:4350–6). Contrary to most other COG-CDG cases, the patient presented a mild/moderate phenotype, i.e. moderate psychomotor retardation with language delay, truncal ataxia and slight hypotonia.MethodsCDG-IIx patients from our database were screened for mutations in COG5. Clinical data were compared. Brefeldin A treatment of fibroblasts and immunoblotting experiments were performed to support the diagnosis.Results and conclusionWe identified five new patients with proven COG5 deficiency. We conclude that the clinical picture is not always as mild as previously described. It rather comprises a broad spectrum with phenotypes ranging from mild to very severe. Interestingly, on a clinical basis some of the patients present a significant overlap with COG7-CDG, a finding which can probably be explained by subunit interactions at the protein level.

Neuromyelitis optica-IgG(+) optic neuritis associated with celiac disease and dysgammaglobulinemia: A role for tacrolimus?

We present a pediatric case of recurrent optic neuritis, celiac disease, partial IgA and IgG3 deficiency in the context of anti-aquaporin-4 auto-immunity and familial IgA deficiency with celiac disease. Treatment with tacrolimus was successful in preventing disease relapses. This case stresses the relevance of central nervous system anti-aquaporin-4 auto-immunity in a broader context of immune dysregulation and neuro-immunology.

NPC1 defect results in abnormal platelet formation and function: studies in Niemann–Pick disease type C1 patients and zebrafish

Niemann-Pick type C is a lysosomal storage disease associated with mutations in NPC1 or NPC2, resulting in an accumulation of cholesterol in the endosomal-lysosomal system. Niemann-Pick type C has a clinical spectrum that ranges from a neonatal rapidly fatal disorder to an adult-onset chronic neurodegenerative disease combined with remarkably, in some cases, hematological defects such as thrombocytopenia, anemia and petechial rash. A role of NPC1 in hematopoiesis was never shown. Here, we describe platelet function abnormalities in three unrelated patients with a proven genetic and biochemical NPC1 defect. Their platelets have reduced aggregations, P-selectin expression and ATP secretions that are compatible with the observed abnormal alpha and reduced dense granules as studied by electron microscopy and CD63 staining after platelet spreading. Their blood counts were normal. NPC1 expression was shown in platelets and megakaryocytes (MKs). In vitro differentiated MKs from NPC1 patients exhibit hyperproliferation of immature MKs with different CD63(+) granules and abnormal cellular accumulation of cholesterol as shown by filipin stainings. The role of NPC1 in megakaryopoiesis was further studied using zebrafish with GFP-labeled thrombocytes or DsRed-labeled erythrocytes. NPC1 depletion in zebrafish resulted in increased cell death in the brain and abnormal cellular accumulation of filipin. NPC1-depleted embryos presented with thrombocytopenia and mild anemia as studied by flow cytometry and real-time QPCR for specific blood cell markers. In conclusion, this is the first report, showing a role of NPC1 in platelet function and formation but further studies are needed to define how cholesterol storage interferes with these processes.

Two novel deletions in hypotonia–cystinuria syndrome

Hypotonia-cystinuria syndrome (HCS) is an autosomal recessive disorder caused by combined deletions of SLC3A1 and PREPL. Clinical features include cystinuria, neonatal hypotonia with spontaneous improvement, poor feeding in neonates, hyperphagia in childhood, growth hormone deficiency, and variable cognitive problems. Only 14 families with 6 different deletions have been reported. Patients are often initially misdiagnosed, while correct diagnosis enables therapeutic interventions. We report two novel deletions, further characterizing the clinical and molecular genetics spectrum of HCS.

PREPL, a prolyl endopeptidase-like enzyme by name only?--Lessons from patients.

Deletion of the Prolyl Endopeptidase-like (PREPL) gene has been described in three contiguous gene deletion syndromes at the 2p21 locus and current developments in high resolution microarrays and whole genome sequencing will no doubt soon result in the identification of isolated PREPL deficiency. But by comparing the differences in phenotypes with the number of genes deleted, the contribution of PREPL deficiency can already be deduced. Homozygous or compound heterozygous loss of PREPL is predicted to cause neonatal hypotonia and severe feeding problems. Failure to thrive usually persists for several years, followed by a period of hyperphagia and excessive weight gain. Growth retardation is usually observed, which responds well to growth hormone therapy. In addition, minor facial dysmorphism, nasal speech, viscous saliva, hypergonadotropic hypogonadism and learning problems are frequently observed. How PREPL deficiency causes these clinical manifestations remains unknown. PREPL is highly expressed in brain and based on gene coexpression network architecture it has been placed in a group enriched with markers of neurons and synaptic proteins. PREPL is predicted to be a serine oligopeptidase based on its homology with prolyl endopeptidase (PREP) and the presence of an active catalytic triad. However, until now no substrates have been found. Recent observations that PREP has non-catalytic functions in the cytoplasm through interactions with its amino- terminal propeller domain, suggests that of PREPL may also have biological functions independent of its predicted peptidase activity. This raises the possibility that PREP and PREPL are homologous, not just by name but also by nature.