François-Guillaume Debray

Long-term Outcome and Clinical Spectrum of 73 Pediatric Patients With Mitochondrial Diseases

OBJECTIVES. We sought to determine the clinical spectrum, survival, and long-term functional outcome of a cohort of pediatric patients with mitochondrial diseases and to identify prognostic factors. METHODS. Medical charts were reviewed for 73 children diagnosed between 1985 and 2005. The functional status of living patients was assessed prospectively by using the standardized Functional Independence Measure scales. RESULTS. Patients fell into 7 phenotypic categories: neonatal-onset lactic acidosis (10%), Leigh syndrome (18%), nonspecific encephalopathy (32%), mitochondrial (encephalo)myopathy (19%), intermittent neurologic (5%), visceral (11%), and Leber hereditary optic neuropathy (5%). Age at first symptoms ranged from prenatal to 16 years (median: 7 months). Neurologic symptoms were the most common (90%). Visceral involvement was observed in 29% of the patients. A biochemical or molecular diagnosis was identified for 81% of the patients as follows: deficiency of complex IV (27%), of pyruvate dehydrogenase or complex I (25% each), of multiple complexes (13%), and of pyruvate carboxylase (5%) or complexes II+III (5%). A mitochondrial DNA mutation was found in 20% of patients. At present, 46% of patients have died (median age: 13 months), 80% of whom were <3 years of age. Multivariate analysis showed that age at first symptoms was a major independent predictor of mortality: patients with first symptoms before 6 months had a highly increased risk of mortality. Cardiac or visceral involvement and neurologic crises were not independent prognostic factors. Living patients showed a wide range of independence levels that correlated positively with age at first symptoms. Among patients aged >5 years (n = 32), 62% had Functional Independence Measure quotients of >0.75. CONCLUSIONS. Mitochondrial diseases in children span a wide range of symptoms and severities. Age at first symptoms is the strongest predictor mortality. Despite a high mortality rate in the cohort, 62% of patients aged >5 years have only mild impairment or normal functional outcome.

Disorders of mitochondrial function

Purpose of review Mitochondrial diseases are a major category of childhood illness that produce a wide variety of symptoms and multisystemic disorders. This review highlights recent clinically important developments in diagnostic evaluation and treatment of mitochondrial diseases. Recent findings Major advances have been made in understanding the genetic bases of mitochondrial diseases. Molecular defects have recently been reported in mitochondrial DNA maintenance, RNA translation and protein import and in mitochondrial fusion and fission, opening new areas of cell disorder. Diagnostic testing is struggling to keep pace with these fundamental discoveries. The diagnostic approach to children suspected of mitochondrial disease is rapidly evolving but few patients have a molecular diagnosis. A better notion of the prognosis of affected children is emerging from studies of long-term outcome. Some therapeutic successes are reported, such as in coenzyme Q deficiency conditions. Summary Mitochondrial diseases can present with signs in almost any organ. Well planned clinical evaluation is the key to successful diagnostic work-up of mitochondrial diseases. An approach is presented for further testing in specialized laboratories. Mitochondrial diseases can be caused by mutations in mitochondrial DNA or, more commonly in children, in nuclear genes. Mitochondrial DNA mutations pose special challenges for genetic counseling and prenatal diagnosis. Supportive treatment and avoidance of environmental stresses are important aspects of patient care. Specific treatment of mitochondrial diseases is in its infancy and is a major challenge for pediatric medicine.

BCOR analysis in patients with OFCD and Lenz microphthalmia syndromes, mental retardation with ocular anomalies, and cardiac laterality defects

Oculofaciocardiodental (OFCD) and Lenz microphthalmia syndromes form part of a spectrum of X-linked microphthalmia disorders characterized by ocular, dental, cardiac and skeletal anomalies and mental retardation. The two syndromes are allelic, caused by mutations in the BCL-6 corepressor gene (BCOR). To extend the series of phenotypes associated with pathogenic mutations in BCOR, we sequenced the BCOR gene in patients with (1) OFCD syndrome, (2) putative X-linked (‘Lenz’) microphthalmia syndrome, (3) isolated ocular defects and (4) laterality phenotypes. We present a new cohort of females with OFCD syndrome and null mutations in BCOR, supporting the hypothesis that BCOR is the sole molecular cause of this syndrome. We identify for the first time mosaic BCOR mutations in two females with OFCD syndrome and one apparently asymptomatic female. We present a female diagnosed with isolated ocular defects and identify minor features of OFCD syndrome, suggesting that OFCD syndrome may be mild and underdiagnosed. We have sequenced a cohort of males diagnosed with putative X-linked microphthalmia and found a mutation, p.P85L, in a single case, suggesting that BCOR mutations are not a major cause of X-linked microphthalmia in males. The absence of BCOR mutations in a panel of patients with non-specific laterality defects suggests that mutations in BCOR are not a major cause of isolated heart and laterality defects. Phenotypic analysis of OFCD and Lenz microphthalmia syndromes shows that in addition to the standard diagnostic criteria of congenital cataract, microphthalmia and radiculomegaly, patients should be examined for skeletal defects, particularly radioulnar synostosis, and cardiac/laterality defects.

Reproduction, smell, and neurodevelopmental disorders: genetic defects in different hypogonadotropic hypogonadal syndromes.

The neuroendocrine control of reproduction in mammals is governed by a neural hypothalamic network of nearly 1500 gonadotropin-releasing hormone (GnRH) secreting neurons that modulate the activity of the reproductive axis across life. Congenital hypogonadotropic hypogonadism (HH) is a clinical syndrome that is characterized by partial or complete pubertal failure. HH may result from inadequate hypothalamic GnRH axis activation, or a failure of pituitary gonadotropin secretion/effects. In man, several genes that participate in olfactory and GnRH neuronal migration are thought to interact during the embryonic life. A growing number of mutations in different genes are responsible for congenital HH. Based on the presence or absence of olfaction dysfunction, HH is divided in two syndromes: HH with olfactory alterations [Kallmann syndrome (KS)] and idiopathic hypogonadotropic hypogonadism (IHH) with normal smell (normosmic IHH). KS is a heterogeneous disorder affecting 1 in 5000 males, with a three to fivefold of males over females. KS is associated with mutations in KAL1, FGFR1/FGF8, FGF17, IL17RD, PROK2/PROKR2, NELF, CHD7, HS6ST1, FLRT3, SPRY4, DUSP6, SEMA3A, NELF, and WDR11 genes that are related to defects in neuronal migration. These reproductive and olfactory deficits include a variable non-reproductive phenotype, including sensorineural deafness, coloboma, bimanual synkinesis, craniofacial abnormalities, and/or renal agenesis. Interestingly, defects in PROKR2, FGFR1, FGF8, CHD7, DUSP6, and WDR11 genes are also associated with normosmic IHH, whereas mutations in KISS1/KISSR, TAC3/TACR3, GNRH1/GNRHR, LEP/LEPR, HESX1, FSHB, and LHB are only present in patients with normosmic IHH. In this paper, we summarize the reproductive, neurodevelopmental, and genetic aspects of HH in human pathology.

LRPPRC mutations cause a phenotypically distinct form of Leigh syndrome with cytochrome c oxidase deficiency

Background The natural history of all known patients with French-Canadian Leigh disease (Saguenay-Lac-St-Jean cytochrome c oxidase deficiency, MIM220111, SLSJ-COX), the largest known cohort of patients with a genetically homogeneous, nuclear encoded congenital lactic acidosis, was studied. Results 55 of 56 patients were homozygous for the A354V mutation in LRPPRC. One was a genetic compound (A354V/C1277Xdel8). Clinical features included developmental delay, failure to thrive, characteristic facial appearance and, in 90% of patients, acute crises that have not previously been detailed, either metabolic (fulminant lactic acidosis) and/or neurological (Leigh syndrome and/or stroke-like episodes). Survival ranged from 5 days to >30 years. 46/56 patients (82%) died, at a median age of 1.6 years. Of 73 crises, 38 (52%) were fatal. The immediate causes of death were multiple organ failure and/or Leigh disease. Major predictors of mortality during crises (p<0.005) were hyperglycaemia, hepatic cytolysis, and altered consciousness at admission. Compared to a group of SURF1-deficient Leigh syndrome patients assembled from the literature, SLSJ-COX is distinct by the occurrence of metabolic crises, leading to earlier and higher mortality (p=0.001). Conclusion SLSJ-COX is clinically distinct, with acute fatal acidotic crises on a backdrop of chronic moderate developmental delay and hyperlactataemia. Leigh syndrome is common. Stroke-like episodes can occur. The Leigh syndrome of SLSJ-COX differs from that of SURF1-related COX deficiency. SLSJ-COX has a different spectrum of associated abnormalities, acidotic crises being particularly suggestive of LRPPRC related Leigh syndrome. Even among A354V homozygotes, pronounced differences in survival and severity occur, showing that other genetic and/or environmental factors can influence outcome.

Hepatocyte transplantation using the domino concept in a child with Tetrabiopterin non-responsive phenylketonuria.

Phenylketonuria is a metabolic disease caused by phenylalanine hydroxylase deficiency. Treatment is based on a strict natural protein-restricted diet that is associated with the risk of malnutrition and severe psychosocial burden. Oral administration of tetrahydrobiopterin can increase residual enzyme activity, but most patients with severe clinical phenotypes are nonresponders. We performed liver cell transplantation in a 6-year-old boy with severe tetrahydrobiopterin nonresponsive phenylketonuria who failed to comply with diet prescriptions. The transplanted hepatocytes were obtained in part from an explanted glycogen storage type 1b liver. Following two infusions, blood phenylalanine levels returned within the therapeutic target while the phenylalanine half-life assessed by loading tests decreased from 43 to 19 h. However, 3 months later, blood phenylalanine concentrations increased and the phenylalanine intake had to be reduced. Cell-based therapy is a promising therapeutic option in phenylketonuria, and the domino concept may solve the issue of cell sources for hepatocyte transplantation.

Mutation of the iron-sulfur cluster assembly gene IBA57 causes fatal infantile leukodystrophy

Leukodystrophies are a heterogeneous group of severe genetic neurodegenerative disorders. A multiple mitochondrial dysfunctions syndrome was found in an infant presenting with a progressive leukoencephalopathy. Homozygosity mapping, whole exome sequencing, and functional studies were used to define the underlying molecular defect. Respiratory chain studies in skeletal muscle isolated from the proband revealed a combined deficiency of complexes I and II. In addition, western blotting indicated lack of protein lipoylation. The combination of these findings was suggestive for a defect in the iron-sulfur (Fe/S) protein assembly pathway. SNP array identified loss of heterozygosity in large chromosomal regions, covering the NFU1 and BOLA3, and the IBA57 and ABCB10 candidate genes, in 2p15-p11.2 and 1q31.1-q42.13, respectively. A homozygous c.436C > T (p.Arg146Trp) variant was detected in IBA57 using whole exome sequencing. Complementation studies in a HeLa cell line depleted for IBA57 showed that the mutant protein with the semi-conservative amino acid exchange was unable to restore the biochemical phenotype indicating a loss-of-function mutation of IBA57. In conclusion, defects in the Fe/S protein assembly gene IBA57 can cause autosomal recessive neurodegeneration associated with progressive leukodystrophy and fatal outcome at young age. In the affected patient, the biochemical phenotype was characterized by a defect in the respiratory chain complexes I and II and a decrease in mitochondrial protein lipoylation, both resulting from impaired assembly of Fe/S clusters.

Mutation Update of the CLCN5 Gene Responsible for Dent Disease 1

Dent disease is a rare X‐linked tubulopathy characterized by low molecular weight proteinuria, hypercalciuria, nephrocalcinosis and/or nephrolithiasis, progressive renal failure, and variable manifestations of other proximal tubule dysfunctions. It often progresses over a few decades to chronic renal insufficiency, and therefore molecular characterization is important to allow appropriate genetic counseling. Two genetic subtypes have been described to date: Dent disease 1 is caused by mutations of the CLCN5 gene, coding for the chloride/proton exchanger ClC‐5; and Dent disease 2 by mutations of the OCRL gene, coding for the inositol polyphosphate 5‐phosphatase OCRL‐1. Herein, we review previously reported mutations (n = 192) and their associated phenotype in 377 male patients with Dent disease 1 and describe phenotype and novel (n = 42) and recurrent mutations (n = 24) in a large cohort of 117 Dent disease 1 patients belonging to 90 families. The novel missense and in‐frame mutations described were mapped onto a three‐dimensional homology model of the ClC‐5 protein. This analysis suggests that these mutations affect the dimerization process, helix stability, or transport. The phenotype of our cohort patients supports and extends the phenotype that has been reported in smaller studies.

Reduced brain choline in homocystinuria due to remethylation defects

Objective: To investigate whether secondary impairment of the transmethylation pathway is a mechanism underlying the neurologic involvement in homocystinuria due to remethylation defects. Methods: Twelve patients with neurologic disease due to remethylation defects were examined by brain magnetic resonance spectroscopic imaging (1H MRSI). Brain N-acetylaspartate, choline-containing compounds (Cho), and creatine (Cr) were quantified and compared to with controls. Metabolites of remethylation cycle and creatine biosynthesis pathway were measured in plasma and urine. Results: MRSI revealed isolated Cho deficiency in all regions examined (mean concentration units ± SD, patients vs controls): frontal white matter (0.051 ± 0.010 vs 0.064 ± 0.010; p = 0.001), lenticular nucleus (0.056 ± 0.011 vs 0.069 ± 0.009; p < 0.001), and thalamus (0.063 ± 0.010 vs 0.071 ± 0.007; p = 0.006). In contrast to controls, the Cho/Cr ratio decreased with age in patients in the three brain regions examined. Low creatine urinary excretion (p < 0.005), normal urine and plasma guanidinoacetate, and a paradoxical increase in plasma S-adenosylmethionine (p < 0.005) concentrations were observed. Conclusion: Patients with homocystinuria due to remethylation defects have an isolated brain choline deficiency, probably secondary to depletion of labile methyl groups produced by the transmethylation pathway. Although biochemical studies suggest mild peripheral creatine deficiency, brain creatine is in the reference range, indicating a possible compartmentation phenomenon. Paradoxical increase of S-adenosylmethionine suggests that secondary inhibition of methylases contributes to the transmethylation defect in these conditions.

Neonatal Liver Cirrhosis Without Iron Overload Caused by Gestational Alloimmune Liver Disease

Gestational alloimmune liver disease has emerged as the major cause of antenatal liver injury and failure. It usually manifests as neonatal liver failure with hepatic and extrahepatic iron overload, a clinical presentation called neonatal hemochromatosis. We report on a newborn in whom fetal hepatomegaly was detected during pregnancy and who presented at birth with liver cirrhosis and mild liver dysfunction. Liver biopsy showed the absence of iron overload but strong immunostaining of hepatocytes for the C5b-9 complex, the terminal complement cascade neoantigen occurring specifically during complement activation by the immunoglobulin G-mediated classic pathway, which established the alloimmune nature of the hepatocyte injury. The infant survived with no specific therapy, and follow-up until 36 months showed progressive normalization of all liver parameters. This case report expands the recognized clinical spectrum of congenital alloimmune liver disease to include neonatal liver disease and cirrhosis, even in the absence of siderosis. Such a diagnosis is of utmost importance regarding the necessity for immunotherapy in further pregnancies to avoid recurrence of alloimmune injury.