Jan Loeffen

Isolated complex I deficiency in children: clinical, biochemical and genetic aspects.

We retrospectively examined clinical and biochemical characteristics of 27 patients with isolated enzymatic complex I deficiency (established in cultured skin fibroblasts) in whom common pathogenic mtDNA point mutations and major rearrangements were absent. Clinical phenotypes present in this group are Leigh syndrome (n = 7), Leigh‐like syndrome (n = 6), fatal infantile lactic acidosis (n = 3), neonatal cardiomyopathy with lactic acidosis (n = 3), macrocephaly with progressive leukodystrophy (n = 2), and a residual group of unspecified encephalomyopathy (n = 6) subdivided into progressive (n = 4) and stable (n = 2) variants. Isolated complex I deficiency is one of the most frequently observed disturbance of the OXPHOS system. Respiratory chain enzyme assays performed in cultured fibroblasts and skeletal muscle tissue in general reveal similar results, but for complete diagnostics we recommend enzyme measurements performed in at least two different tissues to minimize the possibility of overlooking the enzymatic diagnosis. Lactate levels in blood and CSF and cerebral CT/MRI studies are highly informative, although normal findings do not exclude complex I deficiency. With the discovery of mutations in nuclear encoded complex I subunits, adequate pre‐ and postnatal counseling becomes available. Finally, considering information currently available, isolated complex I deficiency in children seems to be caused in the majority by mutations in nuclear DNA. Hum Mutat 15:123–134, 2000.

The First Nuclear-Encoded Complex I Mutation in a Patient with Leigh Syndrome

Nicotinamide adenine dinucleotide (NADH):ubiquinone oxidoreductase (complex I) is the largest multiprotein enzyme complex of the respiratory chain. The nuclear-encoded NDUFS8 (TYKY) subunit of complex I is highly conserved among eukaryotes and prokaryotes and contains two 4Fe4S ferredoxin consensus patterns, which have long been thought to provide the binding site for the iron-sulfur cluster N-2. The NDUFS8 cDNA contains an open reading frame of 633 bp, coding for 210 amino acids. Cycle sequencing of amplified NDUFS8 cDNA of 20 patients with isolated enzymatic complex I deficiency revealed two compound heterozygous transitions in a patient with neuropathologically proven Leigh syndrome. The first mutation was a C236T (P79L), and the second mutation was a G305A (R102H). Both mutations were absent in 70 control alleles and cosegregated within the family. A progressive clinical phenotype proceeding to death in the first months of life was expressed in the patient. In the 19 other patients with enzymatic complex I deficiency, no mutations were found in the NDUFS8 cDNA. This article describes the first molecular genetic link between a nuclear-encoded subunit of complex I and Leigh syndrome.

Demonstration of a New Pathogenic Mutation in Human Complex I Deficiency: A 5-bp Duplication in the Nuclear Gene Encoding the 18-kD (AQDQ) Subunit

We report the cDNA cloning, chromosomal localization, and a mutation in the human nuclear gene encoding the 18-kD (AQDQ) subunit of the mitochondrial respiratory chain complex I. The cDNA has an open reading frame of 175 amino acids and codes for a protein with a molecular mass of 23.2 kD. Its gene was mapped to chromosome 5. A homozygous 5-bp duplication, destroying a consensus phosphorylation site, in the 18-kD cDNA was found in a complex I-deficient patient. The patient showed normal muscle morphology and a remarkably nonspecific fatal progressive phenotype without increased lactate concentrations in body fluids. The childs parents were heterozygous for the mutation. In 19 other complex I-deficient patients, no mutations were found in the 18-kD gene.

Leigh syndrome associated with a mutation in the NDUFS7 (PSST) nuclear encoded subunit of complex I

Leigh syndrome is the phenotypical expression of a genetically heterogeneous cluster of disorders, with pyruvate dehydrogenase complex deficiency and respiratory chain disorders as the main biochemical causes. We report the first missense mutation within the nuclear encoded complex I subunit, NDUFS7, in 2 siblings with neuropathologically proven complex I–deficient Leigh syndrome. Ann Neurol 1999;45:787–790

Mutations in the complex I NDUFS2 gene of patients with cardiomyopathy and encephalomyopathy.

Human complex I is built up and regulated by genes encoded by the mitochondrial DNA (mtDNA) as well as the nuclear DNA (nDNA). In recent years, attention mainly focused on the relation between complex I deficiency and mtDNA mutations. However, a high percentage of consanguinity and an autosomal‐recessive mode of inheritance observed within our patient group as well as the absence of common mtDNA mutations make a nuclear genetic cause likely. The NDUFS2 protein is part of complex I of many pro‐ and eukaryotes. The nuclear gene coding for this protein is therefore an important candidate for mutational detection studies in enzymatic complex I deficient patients. Screening of patient NDUFS2 cDNA by reverse transcriptase–polymerase chain reaction (RT‐PCR) in combination with direct DNA sequencing revealed three missense mutations resulting in the substitution of conserved amino acids in three families. Ann Neurol 2001;49:195–201

Intrathecal rituximab treatment for pediatric post-transplant lymphoproliferative disorder of the central nervous system

Post‐transplant lymphoproliferative disorder (PTLD) in the central nervous system (CNS) has a poor prognosis. New therapeutic approaches should be explored. We report our experience with intrathecal administration of rituximab in a 10‐year‐old kidney allograft recipient with PTLD in the CNS. After standard treatment had failed, we tried to treat the patient by administering rituximab directly into the cerebral ventricle through an Omaya reservoir, in addition to conventional intrathecal and systemic chemotherapy. This strategy resulted in a disappearance of clinical symptoms and a negative positron emission tomogram. Intrathecal administration of rituximab may be a feasible approach in children with PTLD in the CNS. However, its specific role in our patient remains uncertain. Pediatr Blood Cancer 2008;50:886–888.

The human nuclear-encoded acyl carrier subunit (NDUFAB1) of the mitochondrial complex I in human pathology.

We present the cDNA sequence of the human mitochondrial acyl carrier protein NDUFAB1, a nuclear-encoded subunit of complex I of the mitochondrial respiratory chain. We obtained the NDUFAB1 cDNA using the cDNA sequence of the bovine mitochondrial acyl carrier protein. The human cDNA contains two putative translation initiation codons. The human NDUFAB1 protein contains a phosphopantetheine attachment site (DLGLDSLDQVEIIMAM), unique for acyl carrier proteins, and an EF-hand calcium binding domain (DIDAEKLMCPQEI). Transcripts of this gene are found in a wide range of human tissues. The highest expression levels were observed, in descending order, in adult heart, skeletal muscle and fetal heart. We subjected NDUFAB1 fibroblast cDNA of 20 patients with an isolated enzymatic complex I deficiency to mutational detection. No mutations in the NDUFAB1 open reading frame were observed. Future studies will answer whether mutations in the NDUFAB1 promoter or transcription elements are responsible for the observed complex I deficiency.

Recognition of genetic predisposition in pediatric cancer patients: An easy-to-use selection tool

Genetic predisposition for childhood cancer is under diagnosed. Identifying these patients may lead to therapy adjustments in case of syndrome-related increased toxicity or resistant disease and syndrome-specific screening programs may lead to early detection of a further independent malignancy. Cancer surveillance might also be warranted for affected relatives and detection of a genetic mutation can allow for reproductive counseling. Here we present an easy-to-use selection tool, based on a systematic review of pediatric cancer predisposing syndromes, to identify patients who may benefit from genetic counseling. The selection tool involves five questions concerning family history, the type of malignancy, multiple primary malignancies, specific features and excessive toxicity, which results in the selection of those patients that may benefit from referral to a clinical geneticist.

Effectiveness of High Fidelity Video-Assisted Real-Time Simulation: A Comparison of Three Training Methods for Acute Pediatric Emergencies

Background. Video-assisted real-time simulation (VARS) offers the possibility of developing competence in acute medicine in a realistic and safe environment. We investigated the effectiveness of the VARS model and compared it with educational methods like Problem-Based Learning (PBL) and Pediatric Advanced Life Support (PALS). Methods. 45 fourth-year medical students were randomized for three educational methods. Level of knowledge and self-efficacy were measured before and after intervention. Clinical performance was measured by a blinded observer using a video checklist of prescripted scenarios on a high-fidelity simulator. Results. Knowledge test and self-efficacy scores improved significantly (P < 0.001) without differences between educational groups. The VARS group showed significantly (P < 0.05) higher scores on both postintervention scenarios concerning structure and time. Conclusion. VARS training is an effective educational method teaching pediatric acute care skills in the undergraduate curriculum. When compared to PBL and PALS training, VARS training appears to be superior in enhancing short-term clinical performance.

Fumarase deficiency presenting with periventricular cysts.

SummaryA fumarase-deficient patient expressed a novel phenotype of congenital cerebral ventricular dilatation and periventricular cysts. The patient was a compound heterozygote for two mutations that are the only ones among the 12 published mutations that have been found in multiple, unrelated, fumarase-deficient patients.