Glutaryl-CoA dehydrogenase mutations in glutaric acidemia (type I): Review and report of thirty novel mutations

Glutaric acidemia type I (GA1) is caused by mutations in the gene encoding the enzyme glutaryl-CoA dehydrogenase (GCD). Sixty-three pathogenic mutations identified by several laboratories are presented, 30 of them for the first time, together with data on expression in Escherichia coli and relationship to the clinical and biochemical phenotype. In brief, many GCD mutations cause GA1, but none is common. There is little if any relationship between genotype and clinical phenotype, but some mutations, even when heterozygous, seem especially common in patients with normal or only minimally elevated urine glutaric acid. Hum Mutat 12:141–144, 1998. © 1998 Wiley-Liss, Inc.     

五例戊二酸血症I型患者GCDH基因突变的分子诊断CSCD

目的探讨5例戊二酸血症I型（glutaric acidemiatype I,GA—I）患者的GCDH基因突变情况,为临床诊治提供参考依据。方法应用Sanger测序法对泉州地区5例GA—I患者GcDH基因的所有外显子及侧翼内含子进行测序,并对测得序列进行分析,以寻找可能的致病突变位点。结果5例患者均检测到GCDH基因突变,共检测到4种突变位点,包括2种错义突变[c．532G〉A（P．G178R）、C．533G〉A（P．G178E）]和2种移码突变Ee．106—107delAC（P．Q37fs＊5）、C．1244—2A〉c]。其中,c．1244—2A〉C突变频率最高～C106—107delAC为未见报道的新突变,MutationTaster软件预测其为致病性突变。结论本研究分析了5例戊二酸血症I型患者的GCDH基因突变情况,从基因水平上证实了临床诊断,发现1个新的GCDH基因突变位点,丰富了GCDH基因的突变谱。     

High frequency of ETFDH c.250G>A mutation in Taiwanese patients with late‐onset lipid storage myopathy

Lan M‐Y, Fu M‐H, Liu Y‐F, Huang C‐C, Chang Y‐Y, Liu J‐S, Peng C‐H, Chen S‐S. High frequency of ETFDH c.250G>A mutation in Taiwanese patients with late‐onset lipid storage myopathy. Lipid storage myopathies (LSMs) are characterized pathologically by the accumulation of lipid droplets in muscle fibers due to impaired cellular lipid metabolism. The purpose of this study was to determine etiologies and genetic mutations associated with LSMs in ethnic Han Taiwanese. The usefulness of the blood acylcarnitine (AC) profile for diagnosing LSMs in adult patients was also investigated. Nine patients were diagnosed with late‐onset LSMs following a review of muscle biopsies and medical records and were recruited retrospectively. Genetic studies were performed to detect mutations in the SLC22A5 for primary carnitine deficiency, PNPLA2 for neutral lipid storage disease with myopathy, ABHD5 for neutral lipid storage disease with ichthyosis, ETFDH for multiple acyl‐CoA dehydrogenation deficiency (MADD), and CPT2 for carnitine palmitoyltransferase II deficiency. Blood AC levels were measured by tandem mass spectrometry. The mutation c.250G>A in ETFDH was detected in seven (78%) patients, six of whom were homozygous for the variant. Patients with ETFDH mutations had elevated blood levels of ACs ranging from C8 to C16 species, a pattern consistent with MADD. ETFDH c.250G>A mutation is common in Taiwanese patients with late‐onset LSMs. The blood AC profile is a sensitive biochemical marker for diagnosing MADD arising from ETFDH mutations in adults.     

Clinical, pathological, and biochemical studies in a patient with propionic acidemia and fatal cardiomyopathy

A patient diagnosed at 9 months with a milder form of propionic acidemia was functioning at a near normal intellectual level and a normal neurological level at age 8. After 2-week history of feeling "poorly" but functioning normally, she became acutely ill and succumbed to heart failure and ventricular fibrillation in 12 h. At post-mortem the heart was hypertrophied and had low carnitine levels, despite carnitine supplementation and repeatedly normal plasma carnitine levels. The findings in this patient provide a possible mechanism for the cardiac complications that are becoming more apparent in propionic acidemia.     

Ocular albinism with infertility and late‐onset sensorineural hearing loss

Ocular albinism type 1 (OA1) is caused by mutations in the GPR143 gene located at Xp22.2. The manifestations, which are due to hypopigmentation, are confined to the eyes and optic pathway. OA1 associated with late‐onset sensorineural hearing loss was previously reported in a single family and hypothesized to be caused by a contiguous gene deletion syndrome involving GPR143 and the adjacent gene, TBL1X. Here, we report on a family with OA1, infertility, late‐onset sensorineural hearing loss, and a small interstitial Xp microdeletion including the GPR143, TBL1X, and SHROOM2 genes. In addition, we re‐examined a patient previously described with OA1, infertility and a similar Xp deletion with audiologic follow‐up showing a late‐onset sensorineural hearing loss. Our results raise an intriguing question about the possibility for TBL1X (absence) involvement in this type of hearing loss. However, our study cannot claim a causative relationship and more convincing evidence is needed before the hypothesis can be accepted that TBL1X could be involved in late‐onset sensorineural hearing loss and that ocular albinism with late‐onset sensorineural hearing loss can present itself as a contiguous gene deletion/microdeletion syndrome. The finding of infertility in all affected male patients demonstrates that this deletion, including the SHROOM2 gene, may be a potentially causative X‐linked genetic factor of male infertility.     

Two Siblings with Homozygous Pathogenic Splice‐Site Variant in Mitochondrial Asparaginyl–tRNA Synthetase (NARS2)

A homozygous missense mutation (c.822G>C) was found in the gene encoding the mitochondrial asparaginyl–tRNA synthetase (NARS2) in two siblings born to consanguineous parents. These siblings presented with different phenotypes: one had mild intellectual disability and epilepsy in childhood, whereas the other had severe myopathy. Biochemical analysis of the oxidative phosphorylation (OXPHOS) complexes in both siblings revealed a combined complex I and IV deficiency in skeletal muscle. In‐gel activity staining after blue native‐polyacrylamide gel electrophoresis confirmed the decreased activity of complex I and IV, and, in addition, showed the presence of complex V subcomplexes. Considering the consanguineous descent, homozygosity mapping and whole‐exome sequencing were combined revealing the presence of one single missense mutation in the shared homozygous region. The c.822G>C variant affects the 3′ splice site of exon 7, leading to skipping of the whole exon 7 and a part of exon 8 in the NARS2 mRNA. In EBV‐transformed lymphoblasts, a specific decrease in the amount of charged mt‐tRNA^Asn was demonstrated as compared with controls. This confirmed the pathogenic nature of the variant. To conclude, the reported variant in NARS2 results in a combined OXPHOS complex deficiency involving complex I and IV, making NARS2 a new member of disease‐associated aaRS2.     

Mitochondrial anomalies in a Swiss family with autosomal dominant myoglobinuria

We report on a Swiss family in which 10 individuals of both sexes in 4 successive generations suffered from myoglobinuria, precipitated by febrile illness. It is the second family described with autosomal dominant inheritance of myoglobinuria. Four individuals suffered acute renal failure, which in two was reversible only after dialysis. In a recent case, a mitochondrial disorder was suspected because of an abnormal increase in lactate levels during an exercise test and because of a subsarcolemmal accumulation of mitochondria in a muscle biopsy, associated with a lack of cytochrome C oxidase in some muscle fibers. No mutation in the mitochondrial DNA was identified. Along with the inheritance pattern, these findings suggest that the myoglobinuria in this family is caused by a nuclear-encoded mutation affecting the respiratory chain. Am. J. Med. Genet. 69:365–369, 1997. © 1997 Wiley-Liss, Inc.     

Mitochondrial DNA variations in patients with Type 2 (non‐insulin dependent) diabetes mellitus and a Welsh control population

Type 2 (non‐insulin dependent) diabetes mellitus may be inherited along the maternal line and a variety of mitochondrial DNA (mtDNA) variants have been implicated in the pathogenesis. We have previously reported mutations in five regions of the mitochondrial genome which encompass 11 of the 22 tRNA genes. Now we employ the technique of single stranded conformational polymorphism (SSCP) analysis to investigate a further 6 regions of the mitochondrial genome, covering the remaining 11 tRNA genes in 40 patients with Type 2 diabetes and 30 racially‐matched normal controls. A variety of homoplasmic mutations were detected in patients with diabetes and these will be of value in further population association studies. Hum Mutat 13:412–413, 1999. © 1999 Wiley‐Liss, Inc.     

P300 amplitude reduction is associated with early‐onset and late‐onset pathological substance use in a prospectively studied cohort of 14‐year‐old adolescents

P3 amplitude reduction (P3AR) is associated with risk for adolescent‐onset pathological substance use (PSU). In this longitudinal study, data from over 1,100 adolescent twins were used to examine P3AR in relation to early adolescent onset PSU (i.e., by age 14), late adolescent onset PSU (i.e., ages 14–18), misuse of different classes of substances (PSU‐nicotine, PSU‐alcohol, PSU‐illicit), degree of PSU comorbidity, and gender differences. P3 amplitude was recorded at age 14 from two midline electrodes during a visual oddball paradigm. PSU was defined as meeting criteria for any symptom of a substance use disorder assessed using semistructured clinical interviews. P3AR was associated with degree of drug class comorbidity, early adolescent onset PSU for all three substance classes, and late adolescent onset PSU for alcohol and illicit PSU. Gender differences in P3AR were not statistically significant. These findings provide further evidence that P3AR indexes a nonspecific diathesis for adolescent‐onset PSU.     

Maternal riboflavin deficiency, resulting in transient neonatal-onset glutaric aciduria Type 2, is caused by a microdeletion in the riboflavin transporter gene GPR172B

Riboflavin, or vitamin B2, is a precursor to flavin adenine dinucleotide (FAD) and flavin mononucleotide (FMN) molecules, required in biological oxidation-reduction reactions. We previously reported a case of a newborn female who had clinical and biochemical features of multiple acyl-CoA dehydrogenation deficiency (MADD), which was corrected by riboflavin supplementation. The mother was then found to be persistently riboflavin deficient, suggesting that a possible genetic defect in riboflavin transport in the mother was the cause of the transient MADD seen in the infant. Two recently-identified riboflavin transporters G protein-coupled receptor 172B (GPR172B or RFT1) and riboflavin transporter 2 (C20orf54 or RFT2) were screened for mutations. Two missense sequence variations, c.209A>G [p.Q70R] and c.886G>A [p.V296M] were found in GPR172B. In vitro functional studies of both missense variations showed that riboflavin transport was unaffected by these variations. Quantitative real-time PCR revealed a de novo deletion in GPR172B spanning exons 2 and 3 in one allele from the mother. We postulate that haploinsufficiency of this riboflavin transporter causes mild riboflavin deficiency, and when coupled with nutritional riboflavin deficiency in pregnancy, resulted in the transient riboflavin-responsive disease seen in her newborn infant. This is the first report of a genetic defect in riboflavin transport in humans.     

Distinct craniofacial‐skeletal‐dermatological dysplasia in a patient with W290C mutation in FGFR2

Mutations in the fibroblast growth factor receptor genes (FGFR) have been known to be associated with many craniosynostosis syndromes with overlapping phenotypes. We studied a 15‐year‐old Thai boy with an unspecified craniosynostosis syndrome characterized by multiple suture craniosynostoses, a persistent anterior fontanel, corneal scleralization, choanal stenosis, atresia of the auditory meatus, broad thumbs and great toes, severe scoliosis, acanthosis nigricans, hydrocephalus, and mental retardation. Radiography revealed bony ankyloses of vertebral bodies of T9–12, humero‐radio‐ulnar joints, intercarpal joints, distal interphalangeal joints of fifth fingers, fibulo‐tibial joints, intertarsal joints, and distal interphalangeal joints of the first toes. The patient was a heterozygous for a 870G → T change resulting in a W290C amino acid substitution in the extracellular domain of the fibroblast growth factor receptor 2 gene (FGFR2). This mutation has previously been reported in a patient with severe Pfeiffer syndrome type 2 that is distinct from the craniosynostosis in our patient. These findings emphasize locus, allelic, and phenotypic heterogeneity of craniofacial‐skeletal‐dermatological syndrome due to FGFR2 mutations. © 2002 Wiley‐Liss, Inc.     

Mutation in SSUH2 Causes Autosomal‐Dominant Dentin Dysplasia Type I

Dentin dysplasia type I (DDI) is an autosomal‐dominant genetic disorder resulting from dentin defects. The molecular basis of DDI remains unclear. DDI exhibits unique characteristics with phenotypes featuring obliteration of pulp chambers and diminutive root, thus providing a useful model for understanding the genetics of tooth formation. Using a large Chinese family with 14 DDI patients, we mapped the gene locus responsible for DDI to 3p26.1–3p24.3 and further identified a missense mutation, c.353C>A (p.P118Q) in the SSUH2 gene on 3p26.1, which co‐segregated with DDI. We showed that SSUH2 (p.P118Q) perturbed the structure and significantly reduced levels of mutant (MT) protein and mRNA compared with wild‐type SSUH2 . Furthermore, MT P141Q knock‐in mice (+/? and ?/?) had a unique partial obliteration of the pulp cavity and upregulation or downregulation of six major genes involved in odontogenesis: Dspp , Dmp1 , Runx2 , Pax9 , Bmp2 , and Dlx2 . The phenotype of missing teeth was determined in zebrafish with morpholino gene knockdowns and rescued by injection of normal human mRNA. Taken together, our observations demonstrate that SSUH2 disrupts dental formation and that this novel gene, together with other odontogenesis genes, is involved in tooth development.     

A rotenone-sensitive site and H2O2 are key components of hypoxia-sensing in neonatal rat adrenomedullary chromaffin cells

In the perinatal period, adrenomedullary chromaffin cells (AMC) directly sense PO2 and secrete catecholamines during hypoxic stress, and this response is lost in juvenile ( approximately 2 week-old) chromaffin cells following postnatal innervation. Here we tested the hypothesis that a rotenone-sensitive O2-sensor and ROS are involved in the hypoxic response of AMC cultured from neonatal and juvenile rats. In whole-cell recordings, hypoxia (PO2=5-15 mm Hg) inhibited outward current in neonatal AMC; this response was reversed by exogenous H2O2 and mimicked and occluded by intracellular catalase (1000 units/ml), as well as the antioxidants, N-acetyl-L-cysteine (NAC; 50 microM) and Trolox (200 microM). Acute hypoxia decreased ROS levels and stimulated ATP secretion in these cells, as measured by luminol and luciferin-luciferase chemiluminescence, respectively. Of several mitochondrial electron transport chain (ETC) inhibitors tested, only rotenone, a complex I blocker, mimicked and occluded the effects of hypoxia on outward current, cellular ROS, and ATP secretion. Succinate donors, which act as complex II substrates, reversed the effects of hypoxia and rotenone in neonatal AMC. In contrast, in hypoxia-insensitive juvenile AMC, neither NAC nor rotenone stimulated ATP secretion though they both caused a decrease in ROS levels. We propose that O2-sensing by neonatal AMC is mediated by decreased ROS generation via a rotenone-sensitive site that is coupled to outward current inhibition and secretion. Interestingly, juvenile AMC display at least two modifications, i.e. an uncoupling of the O2-sensor from ROS regulation, and an apparent insensitivity of outward current to decreased ROS.     

Type 2B and pseudo type 2B Von Willebrand disease; a report of three cases

Increased affinity of Von Willebrand factor (VWF) for its platelet receptor GPIb-GPIX complex is responsible of an hemorrhagic disease, which is the Von Willebrand disease (VWD) type 2B when the molecular abnormality is located on the VWF, and the platelet-type 2B VWD when the mutation concern the platelet receptor. Haemostatic abnormalities in these bleeding disorders are similar; prolonged bleeding time, fluctuating thrombocytopenia, decreased factor VIII-VWF complex, and an increased response to low dose of ristocetin in platelets rich plasma. High molecular weight VWF multimers are decreased. We report here 2 cases of type 2B VWD and 1 case of platelet type 2B VWD. The distinction between these 2 diseases was established by studying platelet aggregation with weak doses of ristocetin in mixtures of washed platelets (of normal control or patient)+poor platelets plasma (normal or patient). In one case, VWD 2B was discovered late in a 49 years old man, and the factor VIIIC-VWF complex was not diminished. The distinction between these two congenital diseases is important for the treatment of bleeding manifestations which need VWF concentrates infusions in type 2B VWD and administration of platelets concentrates in pseudo type 2B VWD.