Impact of the SARS-CoV-2 pandemic on the health of individuals with intoxication-type metabolic diseases-Data from the E-IMD consortium

The SARS-CoV-2 pandemic challenges healthcare systems worldwide. Within inherited metabolic disorders (IMDs) the vulnerable subgroup of intoxication-type IMDs such as organic acidurias (OA) and urea cycle disorders (UCD) show risk for infection-induced morbidity and mortality. This study (observation period February 2020 to December 2021) evaluates impact on medical health care as well as disease course and outcome of SARS-CoV-2 infections in patients with intoxication-type IMDs managed by participants of the European Registry and Network for intoxication type metabolic diseases Consortium (E-IMD). Survey's respondents managing 792 patients (n = 479 pediatric; n = 313 adult) with intoxication-type IMDs (n = 454 OA; n = 338 UCD) in 14 countries reported on 59 (OA: n = 36; UCD: n = 23), SARS-CoV-2 infections (7.4%). Medical services were increasingly requested (95%), mostly alleviated by remote technologies (86%). Problems with medical supply were scarce (5%). Regular follow-up visits were reduced in 41% (range 10%-50%). Most infected individuals (49/59; 83%) showed mild clinical symptoms, while 10 patients (17%; n = 6 OA including four transplanted MMA patients; n = 4 UCD) were hospitalized (metabolic decompensation in 30%). ICU treatment was not reported. Hospitalization rate did not differ for diagnosis or age group (p = 0.778). Survival rate was 100%. Full recovery was reported for 100% in outpatient care and 90% of hospitalized individuals. SARS-CoV-2 impacts health care of individuals with intoxication-type IMDs worldwide. Most infected individuals, however, showed mild symptoms and did not require hospitalization. SARS-CoV-2-induced metabolic decompensations were usually mild without increased risk for ICU treatment. Overall prognosis of infected individuals is very promising and IMD-specific or COVID-19-related complications have not been observed.

Retained visual function in a subset of patients with long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency (LCHADD)

Introduction: LCHADD causes retinopathy associated with low vision, visual field defects, nyctalopia and myopia. We report a retrospective long-term single-center study of 6 LCHADD patients trying to clarify if early diagnosis has an impact on the course and outcome of chorioretinal degeneration. Methods: Long-term follow-up of visual acuity and staging of chorioretinal degeneration by fundus photography, optical coherence tomography (OCT) and autofluorescence (AF) in all six patients. Three patients (2 m/1 f; age 8-14.8 years) were diagnosed by newborn screening, a single patient early within the first year of life and treated promptly while the other two (1 m/1 f; age 23-24 years) were diagnosed later after developing symptoms. All carried HADHA variants; five were homozygous for the common p.E510Q variant, in one from the symptomatically diagnosed group p.[E510Q]; [R291*] was detected. Results: All patients showed retinal alterations, but early diagnosis was associated with a milder phenotype and a longer preservation of visual function. Among symptomatic patients, only one showed mild retinal involvement at the time of diagnosis. Conclusion: Despite the small number our study suggests that early diagnosis does not prevent retinopathy but might contribute to a milder phenotype with retained good visual acuity over time. OCT and AF are reliable non-invasive diagnostic tools to estimate the progression of early-stage retinal changes in LCHADD patients.

Computer simulations suggest that acute correction of hyperglycaemia with an insulin bolus protocol might be useful in brain FDG PET

Aim: FDG PET in hyperglycaemic subjects often suffers from limited statistical image quality, which may hamper visual and quantitative evaluation. In our study the following insulin bolus protocol is proposed for acute correction of hyperglycaemia (> 7.0 mmol/l) in brain FDG PET. (i) Intravenous bolus injection of short-acting insulin, one I.E. for each 0.6 mmol/l blood glucose above 7.0. (ii) If 20 min after insulin administration plasma glucose is ≤ 7.0 mmol/l, proceed to (iii). If insulin has not taken sufficient effect step back to (i). Compute insulin dose with the updated blood glucose level. (iii) Wait further 20 min before injection of FDG. (iv) Continuous supervision of the patient during the whole scanning procedure. Methods: The potential of this protocol for improvement of image quality in brain FDG PET in hyperglycaemic subjects was evaluated by computer simulations within the Sokoloff model. A plausibility check of the prediction of the computer simulations on the magnitude of the effect that might be achieved by correction of hyperglycaemia was performed by retrospective evaluation of the relation between blood glucose level and brain FDG uptake in 89 subjects in whom FDG PET had been performed for diagnosis of Alzheimer's disease. Results: The computer simulations suggested that acute correction of hyperglycaemia according to the proposed bolus insulin protocol might increase the FDG uptake of the brain by up to 80%. The magnitude of this effect was confirmed by the patient data. Conclusion: The proposed management protocol for acute correction of hyper glycaemia with insulin has the potential to significantly improve the statistical quality of brain FDG PET images. This should be confirmed in a prospective study in patients.

Progressive deafness-dystonia due to SERAC1 mutations: A study of 67 cases

OBJECTIVE

3-Methylglutaconic aciduria, dystonia-deafness, hepatopathy, encephalopathy, Leigh-like syndrome (MEGDHEL) syndrome is caused by biallelic variants in SERAC1.

METHODS

This multicenter study addressed the course of disease for each organ system. Metabolic, neuroradiological, and genetic findings are reported.

RESULTS

Sixty-seven individuals (39 previously unreported) from 59 families were included (age range = 5 days-33.4 years, median age = 9 years). A total of 41 different SERAC1 variants were identified, including 20 that have not been reported before. With the exception of 2 families with a milder phenotype, all affected individuals showed a strikingly homogeneous phenotype and time course. Severe, reversible neonatal liver dysfunction and hypoglycemia were seen in >40% of all cases. Starting at a median age of 6 months, muscular hypotonia (91%) was seen, followed by progressive spasticity (82%, median onset = 15 months) and dystonia (82%, 18 months). The majority of affected individuals never learned to walk (68%). Seventy-nine percent suffered hearing loss, 58% never learned to speak, and nearly all had significant intellectual disability (88%). Magnetic resonance imaging features were accordingly homogenous, with bilateral basal ganglia involvement (98%); the characteristic "putaminal eye" was seen in 53%. The urinary marker 3-methylglutaconic aciduria was present in virtually all patients (98%). Supportive treatment focused on spasticity and drooling, and was effective in the individuals treated; hearing aids or cochlear implants did not improve communication skills.

INTERPRETATION

MEGDHEL syndrome is a progressive deafness-dystonia syndrome with frequent and reversible neonatal liver involvement and a strikingly homogenous course of disease. Ann Neurol 2017;82:1004-1015.

De Novo Truncating Variants in ASXL2 Are Associated with a Unique and Recognizable Clinical Phenotype

The ASXL genes (ASXL1, ASXL2, and ASXL3) participate in body patterning during embryogenesis and encode proteins involved in epigenetic regulation and assembly of transcription factors to specific genomic loci. Germline de novo truncating variants in ASXL1 and ASXL3 have been respectively implicated in causing Bohring-Opitz and Bainbridge-Ropers syndromes, which result in overlapping features of severe intellectual disability and dysmorphic features. ASXL2 has not yet been associated with a human Mendelian disorder. In this study, we performed whole-exome sequencing in six unrelated probands with developmental delay, macrocephaly, and dysmorphic features. All six had de novo truncating variants in ASXL2. A careful review enabled the recognition of a specific phenotype consisting of macrocephaly, prominent eyes, arched eyebrows, hypertelorism, a glabellar nevus flammeus, neonatal feeding difficulties, hypotonia, and developmental disabilities. Although overlapping features with Bohring-Opitz and Bainbridge-Ropers syndromes exist, features that distinguish the ASXL2-associated condition from ASXL1- and ASXL3-related disorders are macrocephaly, absence of growth retardation, and more variability in the degree of intellectual disabilities. We were also able to demonstrate with mRNA studies that these variants are likely to exert a dominant-negative effect, given that both alleles are expressed in blood and the mutated ASXL2 transcripts escape nonsense-mediated decay. In conclusion, de novo truncating variants in ASXL2 underlie a neurodevelopmental syndrome with a clinically recognizable phenotype. This report expands the germline disorders that are linked to the ASXL genes.

Eyes on MEGDEL: distinctive basal ganglia involvement in dystonia deafness syndrome

Pediatric movement disorders are still a diagnostic challenge, as many patients remain without a (genetic) diagnosis. Magnetic resonance imaging (MRI) pattern recognition can lead to the diagnosis. MEGDEL syndrome (3-MethylGlutaconic aciduria, Deafness, Encephalopathy, Leigh-like syndrome MIM #614739) is a clinically and biochemically highly distinctive dystonia deafness syndrome accompanied by 3-methylglutaconic aciduria, severe developmental delay, and progressive spasticity. Mutations are found in SERAC1, encoding a phosphatidylglycerol remodeling enzyme essential for both mitochondrial function and intracellular cholesterol trafficking. Based on the homogenous phenotype, we hypothesized an accordingly characteristic MRI pattern. A total of 43 complete MRI studies of 30 patients were systematically reevaluated. All patients presented a distinctive brain MRI pattern with five characteristic disease stages affecting the basal ganglia, especially the putamen. In stage 1, T2 signal changes of the pallidum are present. In stage 2, swelling of the putamen and caudate nucleus is seen. The dorsal putamen contains an "eye" that shows no signal alteration and (thus) seems to be spared during this stage of the disease. It later increases, reflecting progressive putaminal involvement. This "eye" was found in all patients with MEGDEL syndrome during a specific age range, and has not been reported in other disorders, making it pathognomonic for MEDGEL and allowing diagnosis based on MRI findings.

CLCN7 and TCIRG1 mutations differentially affect bone matrix mineralization in osteopetrotic individuals

Osteopetrosis is an inherited disorder of impaired bone resorption, with the most commonly affected genes being CLCN7 and TCIRG1, encoding the Cl(-) /H(+) exchanger CLC-7 and the a3 subunit of the vacuolar H(+) -ATPase, respectively. We and others have previously shown that the disease is frequently accompanied by osteomalacia, and that this additional pathology is also found in Tcirg1-deficient oc/oc mice. The remaining question was whether osteoid enrichment is specifically associated with TCIRG1 inactivation, or whether CLCN7 mutations would also cause skeletal mineralization defects. Here we describe a complete osteologic assessment of one family carrying a novel mutation in CLCN7 (D145G), which impairs the activation and relaxation kinetics of the CLC-7 ion transporter. The two siblings carrying the mutation in the homozygous state displayed high bone mass, increased serum levels of bone formation markers, but no impairment of calcium homeostasis when compared to the other family members. Most importantly, however, undecalcified processing of an iliac crest biopsy from one of the affected children clearly demonstrated a pathological increase of trabecular bone mass, but no signs of osteomalacia. Given the potential relevance of these findings we additionally performed undecalcified histology of iliac crest biopsies from seven additional cases with osteopetrosis caused by a mutation in TNFRSF11A (n=1), CLCN7 (n=3), or TCIRG1 (n=3). Here we observed that all cases with TCIRG1-dependent osteopetrosis displayed severe osteoid accumulation and decreased calcium content within the mineralized matrix. In contrast, there was no detectable bone mineralization defect in the cases with TNFRSF11A-dependent or CLCN7-dependent osteopetrosis. Taken together, our analysis demonstrates that CLCN7 and TCIRG1 mutations differentially affect bone matrix mineralization, and that there is a need to modify the current classification of osteopetrosis.

Decreased bone formation and increased osteoclastogenesis cause bone loss in mucolipidosis II

Mucolipidosis type II (MLII) is a severe multi-systemic genetic disorder caused by missorting of lysosomal proteins and the subsequent lysosomal storage of undegraded macromolecules. Although affected children develop disabling skeletal abnormalities, their pathogenesis is not understood. Here we report that MLII knock-in mice, recapitulating the human storage disease, are runted with accompanying growth plate widening, low trabecular bone mass and cortical porosity. Intralysosomal deficiency of numerous acid hydrolases results in accumulation of storage material in chondrocytes and osteoblasts, and impaired bone formation. In osteoclasts, no morphological or functional abnormalities are detected whereas osteoclastogenesis is dramatically increased in MLII mice. The high number of osteoclasts in MLII is associated with enhanced osteoblastic expression of the pro-osteoclastogenic cytokine interleukin-6, and pharmacological inhibition of bone resorption prevented the osteoporotic phenotype of MLII mice. Our findings show that progressive bone loss in MLII is due to the presence of dysfunctional osteoblasts combined with excessive osteoclastogenesis. They further underscore the importance of a deep skeletal phenotyping approach for other lysosomal diseases in which bone loss is a prominent feature.

Propionic acidemia: neonatal versus selective metabolic screening

BACKGROUND

Whereas propionic acidemia (PA) is a target disease of newborn screening (NBS) in many countries, it is not in others. Data on the benefit of NBS for PA are sparse.

STUDY DESIGN

Twenty PA patients diagnosed through NBS were compared to 35 patients diagnosed by selective metabolic screening (SMS) prompted by clinical findings, family history, or routine laboratory test results. Clinical and biochemical data of patients from 16 metabolic centers in Germany, Austria, and Switzerland were evaluated retrospectively. Additionally, assessment of the intelligent quotient (IQ) was performed. In a second step, the number of PA patients who have died within the past 20 years was estimated based on information provided by the participating metabolic centers.

RESULTS

Patients diagnosed through NBS had neither a milder clinical course regarding the number of metabolic crises nor a better neurological outcome. Among NBS patients, 63% were already symptomatic at the time of diagnosis, and <10% of all patients remained asymptomatic. Among all PA patients, 76% were found to be at least mildly mentally retarded, with an IQ <69. IQ was negatively correlated with the number of metabolic decompensations, but not simply with the patients' age. Physical development was also impaired in the majority of patients. Mortality rates tended to be lower in NBS patients compared with patients diagnosed by SMS.

CONCLUSION

Early diagnosis of PA through NBS seems to be associated with a lower mortality rate. However, no significant benefit could be shown for surviving patients with regard to their clinical course, including the number of metabolic crises, physical and neurocognitive development, and long-term complications.

Mutation analysis in 54 propionic acidemia patients

Deficiency of propionyl CoA carboxylase (PCC), a dodecamer of alpha and beta subunits, causes inherited propionic acidemia. We have studied, at the molecular level, PCC in 54 patients from 48 families comprised of 96 independent alleles. These patients of various ethnic backgrounds came from research centers and hospitals in Germany, Austria and Switzerland. The thorough clinical characterization of these patients was described in the accompanying paper (Grünert et al. 2012). In all 54 patients, many of whom originated from consanguineous families, the entire PCCB gene was examined by genomic DNA sequencing and in 39 individuals the PCCA gene was also studied. In three patients we found mutations in both PCC genes. In addition, in many patients RT-PCR analysis of lymphoblast RNA, lymphoblast enzyme assays, and expression of new mutations in E.coli were carried out. Eight new and eight previously detected mutations were identified in the PCCA gene while 15 new and 13 previously detected mutations were found in the PCCB gene. One missense mutation, p.V288I in the PCCB gene, when expressed in E.coli, yielded 134% of control activity and was consequently classified as a polymorphism in the coding region. Numerous new intronic polymorphisms in both PCC genes were identified. This study adds a considerable amount of new molecular data to the studies of this disease.

Neonatal cholestasis and glucose-6-P-dehydrogenase deficiency

We report a Caucasian neonate with chronic non-spherocytic hemolytic anemia due to a class I G6PD deficiency. A novel mutation missense mutation in exon eight of the G6PD gene was detected (c.827C>T p.Pro276Leu). Bilirubin peaked on day 5 at 24 mg/dl with a conjugated bilirubin of 17 mg/dl. Jaundice resolved within 4 weeks. A detailed work-up failed to reveal other specific factors contributing to cholestasis. Severe hemolytic disease of the newborn may cause cholestasis even in the absence of associated primary hepato-biliary disease.

Phenylalanine tolerance in three phenylketonuric women pregnant with fetuses of different genetic PKU status

Pregnancy management in phenylketonuric women includes continuous dietary control starting before conception, aiming to maintain blood phenylalanine concentrations in a desirable range, irrespective of the fetal genetic PKU status. While the maternal phenylalanine hydroxylase (PAH) genotype will influence metabolic control, an effect of the fetal genetic PKU status on maternal metabolic control during pregnancy has not been described. We monitored three pregnancies of women with classical PKU by dietary protocols of daily phenylalanine intake, phenylalanine blood concentrations, and obstetric care. Patients 1 and 2 carried a heterozygous (not PKU-affected) fetus, while patient 3 was pregnant with a PKU-affected fetus (PAH p.R408W and p.R408W). The expected increase in phenylalanine tolerance during the course of pregnancy was observed in patients 1 and 2 in whom phenylalanine intake could be steadily increased from 400 to 1700 mg/day while phenylalanine blood concentrations remained in the desired range. Gain of body weight was 13.0 and 17.7 kg, respectively. In patient 3, the phenylalanine tolerance did not rise above 600 mg/day, and phenylalanine blood concentrations were above the desired range on several occasions. Caloric intake was therefore encouraged, which led to a weight gain of 20.0 kg. The course of pregnancy was otherwise normal in all three cases, and infants with normal birth weight and head circumference were born. The different phenylalanine tolerance in pregnancies with PKU-affected and non-affected fetuses suggests that PAH genotype and metabolic situation of the fetus influence maternal metabolic control. A phenylalanine tolerance remaining low in the third trimester of pregnancy may indicate fetal PKU.

Treatment recommendations in long-chain fatty acid oxidation defects: consensus from a workshop

Published data on treatment of fatty acid oxidation defects are scarce. Treatment recommendations have been developed on the basis of observations in 75 patients with long-chain fatty acid oxidation defects from 18 metabolic centres in Central Europe. Recommendations are based on expert practice and are suggested to be the basis for further multicentre prospective studies and the development of approved treatment guidelines. Considering that disease complications and prognosis differ between different disorders of long-chain fatty acid oxidation and also depend on the severity of the underlying enzyme deficiency, treatment recommendations have to be disease-specific and depend on individual disease severity. Disorders of the mitochondrial trifunctional protein are associated with the most severe clinical picture and require a strict fat-reduced and fat-modified (medium-chain triglyceride-supplemented) diet. Many patients still suffer acute life-threatening events or long-term neuropathic symptoms despite adequate treatment, and newborn screening has not significantly changed the prognosis for these severe phenotypes. Very long-chain acyl-CoA dehydrogenase deficiency recognized in neonatal screening, in contrast, frequently has a less severe disease course and dietary restrictions in many patients may be loosened. On the basis of the collected data, recommendations are given with regard to the fat and carbohydrate content of the diet, the maximal length of fasting periods and the use of l-carnitine in long-chain fatty acid oxidation defects.

Management and outcome in 75 individuals with long-chain fatty acid oxidation defects: results from a workshop

At present, long-chain fatty acid oxidation (FAO) defects are diagnosed in a number of countries by newborn screening using tandem mass spectrometry. In the majority of cases, affected newborns are asymptomatic at time of diagnosis and acute clinical presentations can be avoided by early preventive measures. Because evidence-based studies on management of long-chain FAO defects are lacking, we carried out a retrospective analysis of 75 patients from 18 metabolic centres in Germany, Switzerland, Austria and the Netherlands with special regard to treatment and disease outcome. Dietary treatment is effective in many patients and can prevent acute metabolic derangements and prevent or reverse severe long-term complications such as cardiomyopathy. However, 38% of patients with very long-chain acyl-CoA dehydrogenase (VLCAD) deficiency had intermittent muscle weakness and pain despite adhering to therapy. Seventy-six per cent of patients with disorders of the mitochondrial trifunctional protein (TFP)-complex including long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD) deficiency, had long-term myopathic symptoms. Of these, 21% had irreversible peripheral neuropathy and 43% had retinopathy. The main principle of treatment was a fat-reduced and fat-modified diet. Fat restriction differed among patients with different enzyme defects and was strictest in disorders of the TFP-complex. Patients with a medium-chain fat-based diet received supplementation of essential long-chain fatty acids. l-Carnitine was supplemented in about half of the patients, but in none of the patients with VLCAD deficiency identified by newborn screening. In summary, in this cohort the treatment regimen was adapted to the severity of the underlying enzyme defect and thus differed among the group of long-chain FAO defects.

Computer simulations suggest that acute correction of hyperglycaemia with an insulin bolus protocol might be useful in brain FDG PET

AIM

FDG PET in hyperglycaemic subjects often suffers from limited statistical image quality, which may hamper visual and quantitative evaluation. In our study the following insulin bolus protocol is proposed for acute correction of hyperglycaemia (>7.0 mmol/l) in brain FDG PET. (i) Intravenous bolus injection of short-acting insulin, one I.E. for each 0.6 mmol/l blood glucose above 7.0. (ii) If 20 min after insulin administration plasma glucose is <or=7.0 mmol/l, proceed to (iii). If insulin has not taken sufficient effect step back to (i). Compute insulin dose with the updated blood glucose level. (iii) Wait further 20 min before injection of FDG. (iv) Continuous supervision of the patient during the whole scanning procedure.

METHODS

The potential of this protocol for improvement of image quality in brain FDG PET in hyperglycaemic subjects was evaluated by computer simulations within the Sokoloff model. A plausibility check of the prediction of the computer simulations on the magnitude of the effect that might be achieved by correction of hyperglycaemia was performed by retrospective evaluation of the relation between blood glucose level and brain FDG uptake in 89 subjects in whom FDG PET had been performed for diagnosis of Alzheimer's disease.

RESULTS

The computer simulations suggested that acute correction of hyperglycaemia according to the proposed bolus insulin protocol might increase the FDG uptake of the brain by up to 80%. The magnitude of this effect was confirmed by the patient data.

CONCLUSION

The proposed management protocol for acute correction of hyper glycaemia with insulin has the potential to significantly improve the statistical quality of brain FDG PET images. This should be confirmed in a prospective study in patients.

Severe hypomyelination as the leading neuroradiological sign in a patient with fucosidosis

Fucosidosis is a rare autosomal recessive lysosomal storage disease, resulting from a deficiency of alpha- L-fucosidase. We report on the clinical and MRI findings of a girl with this disorder. Developmental delay became obvious at an age between 6 and 12 months. Cranial MRI at 16 months revealed severe global hypomyelination of both supra- and infratentorial white matter but no involvement of basal ganglia or thalamus. No clinical signs typical for fucosidosis were present at this time, and psychomotor development still progressed slowly. Since the age of 2 years, progressive neurological deterioration occurred. The diagnosis was established by severely decreased activity of alpha- L-fucosidase in plasma and leukocytes and confirmed by the detection of compound heterozygosity for two missense mutations of the FUCA1 gene. A follow-up imaging at the age of 4 years showed progression of neuroradiological abnormalities, particularly progressive involvement of basal ganglia and thalami. The course of this patient and her MRI findings enlarge the clinical and neuroradiological spectrum of fucosidosis.

Elevated serum biotinidase activity in hepatic glycogen storage disorders--a convenient biomarker

An elevated serum biotinidase activity in patients with glycogen storage disease (GSD) type Ia has been reported previously. The aim of this work was to investigate the specificity of the phenomenon and thus we expanded the study to other types of hepatic GSDs. Serum biotinidase activity was measured in a total of 68 GSD patients and was compared with that of healthy controls (8.7 +/- 1.0; range 7.0-10.6 mU/ml; n = 26). We found an increased biotinidase activity in patients with GSD Ia (17.7 +/- 3.9; range: 11.4-24.8; n = 21), GSD I non-a (20.9 +/- 5.6; range 14.6-26.0; n = 4), GSD III (12.5 +/- 3.6; range 7.8-19.1; n = 13), GSD VI (15.4 +/- 2.0; range 14.1-17.7; n = 3) and GSD IX (14.0 +/- 3.8; range: 7.5-21.6; n = 22). The sensitivity of this test was 100% for patients with GSD Ia, GSD I non-a and GSD VI, 62% for GSD III, and 77% for GSD IX, indicating reduced sensitivity for GSD III and GSD IX, respectively. In addition, we found elevated biotinidase activity in all sera from 5 patients with Fanconi-Bickel Syndrome (15.3 +/- 3.7; range 11.0-19.4). Taken together, we propose serum biotinidase as a diagnostic biomarker for hepatic glycogen storage disorders.

Glucose metabolism and insulin secretion in a patient with ABCC8 mutation and Fanconi-Bickel syndrome caused by maternal isodisomy of chromosome 3

Fanconi-Bickel syndrome (FBS) is a rare disorder of glucose transport caused by autosomal recessive mutations in GLUT2. Clinically, FBS results in growth failure, hepatomegaly, renal Fanconi syndrome, and abnormal glucose homeostasis. We report a 23 month old female with FBS characterized by more severe and refractory hypoglycemia than typically seen in this disorder. Although previous reports indicate that FBS patients have diminished insulin secretion, our patient showed evidence of hyperinsulinism (HI). Sequence analysis showed that the patient was homozygous for a known null mutation in GLUT2, confirming the clinical diagnosis of FBS. Parental genotyping showed that the mother was heterozygous for the GLUT2 mutation, while the father was wild type. Tandem repeat marker analysis showed that the patient inherited the GLUT2 mutation via maternal isodisomy of chromosome 3. Further molecular testing showed that the patient was heterozygous for a mutation in ABCC8, a known cause of congenital HI. We discuss the patient's biochemical responses in light of the molecular findings.

High bone mineral density in pycnodysostotic patients with a novel mutation in the propeptide of cathepsin K

INTRODUCTION

Pycnodysostosis is typically associated with short stature, multiple fractures without adequate trauma and high bone density on x-ray. The increased bone density is due to a genetic defect of cathepsin K, leading to dysfunctional osteoclastic bone resorption and bone remodeling. We wanted to know how this defect influences the trabecular and cortical volumetric bone mineral density of long bones as measured quantitatively by pQCT.

METHODS

Three siblings of a consanguineous family were admitted to our hospital because of multiple fractures. Pycnodysostosis was diagnosed based on the clinical presentation with the characteristic dense appearance of their bones on x-ray. The distal and proximal radius of the patients and of control subjects was scanned using a Stratec XCT-2000 pQCT scanner and data were processed using the software provided by the manufacturer. Genomic DNA was extracted from blood samples of all three patients and their parents. The coding exons of the cathepsin K gene (CTSK) were amplified and sequenced.

RESULTS

The patients displayed the typical features of pycnodysostosis: Short stature, delay of closure of the fontanelles, hypoplasia of the maxilla, spondylolysis of the lumbar spine, stubby hands and feet and a history of multiple fractures. Volumetric bone density was much higher in pycnodysostotic bone than in the control bones 686 +/- 28 mg/cm(3) in patients vs. 290 +/- 6 mg/cm(3) in controls; p = 0.001), especially in the trabecular compartment (733 +/- 26 mg/cm(3) in patients vs. 195 +/- 8 mg/cm(3) in controls; p < 0.001), but also in the cortical bone (1108 +/- 22 in patients vs. 1020 +/- 17 in controls; p < 0.01). In contrast to this finding, the patients displayed an elevation of alkaline phosphatase in the serum and free deoxypyridinoline-crosslinks (DPD) in the urine, suggesting osteomalacia. Sequencing of the cathepsin K gene revealed homozygosity for a novel missense mutation in all three patients predicting the amino acid exchange from arginine to tryptophan at position 46 (R46W).

CONCLUSION

We present here for the first time quantitative data on the mineral density of bones of pycnodysostotic patients with a novel mutation in the propeptide of cathepsin K. The elevated bone mineral density in the cortex and the changes in the serum markers suggest an effect of cathepsin K not only on bone volume, but also on bone mineralization. This might in part explain the increased susceptibility to fractures of patients with pycnodysostosis.

Bilateral nuclear cataracts as the first neonatal sign of Fanconi-Bickel syndrome

A patient with early bilateral nuclear cataracts and subsequent diagnosis of Fanconi-Bickel syndrome is described. Despite impaired galactose and glucose metabolism, cataracts have been reported in only few cases with this disorder. We conclude that Fanconi-Bickel syndrome should be considered in the differential diagnosis of neonatal cataracts. The pathogenesis of this complication has not been fully elucidated.

Elevated phenylalanine levels interfere with neurite outgrowth stimulated by the neuronal cell adhesion molecule L1 in vitro

Elevated levels of phenylalanine (Phe) as observed in patients with phenylketonuria interfere with proper neuronal development, leading to severe psychomotor deficits and mental retardation. We have analyzed the effects of Phe on neurite outgrowth in vitro. When expressed in fibroblasts, the neuronal cell adhesion molecules L1 and plexin B3 strongly increase the length of neurites emanating from cerebellar neurons in co-culture experiments. Elevated Phe blocks L1-mediated, but not plexin B3-mediated outgrowth, whereas tyrosine is ineffective. Elevated Phe also interferes with aggregation of fibroblasts overexpressing L1, suggesting that the pathological effect of elevated Phe occurs by interfering with L1-mediated cell adhesion.

Phenotypic spectrum associated with mutations of the mitochondrial polymerase gamma gene

Mutations in the gene coding for the catalytic subunit of the mitochondrial DNA (mtDNA) polymerase gamma (POLG1) have recently been described in patients with diverse clinical presentations, revealing a complex relationship between genotype and phenotype in patients and their families. POLG1 was sequenced in patients from different European diagnostic and research centres to define the phenotypic spectrum and advance understanding of the recurrence risks. Mutations were identified in 38 cases, with the majority being sporadic compound heterozygotes. Eighty-nine DNA sequence changes were identified, including 2 predicted to alter a splice site, 1 predicted to cause a premature stop codon and 13 predicted to cause novel amino acid substitutions. The majority of children had a mutation in the linker region, often 1399G-->A (A467T), and a mutation affecting the polymerase domain. Others had mutations throughout the gene, and 11 had 3 or more substitutions. The clinical presentation ranged from the neonatal period to late adult life, with an overlapping phenotypic spectrum from severe encephalopathy and liver failure to late-onset external ophthalmoplegia, ataxia, myopathy and isolated muscle pain or epilepsy. There was a strong gender bias in children, with evidence of an environmental interaction with sodium valproate. POLG1 mutations cause an overlapping clinical spectrum of disease with both dominant and recessive modes of inheritance. 1399G-->A (A467T) is common in children, but complete POLG1 sequencing is required to identify multiple mutations that can have complex implications for genetic counselling.

Decreased plasma concentration of von Willebrand factor antigen (VWF:Ag) in patients with glycogen storage disease type Ia

Despite highly increased blood lipids, patients with glycogen storage disease type Ia (GSD Ia) do not develop premature vascular complications. Since this could be due to changes of coagulation factors, coagulation tests (including von Willebrand factor (VWF) antigen (VWF:Ag) ELISA, VWF:collagen binding activity (VWF:CB) and VWF multimer analysis) were performed in 10 GSD Ia patients, single cases of other GSD types, and in both healthy and hyperlipidaemic controls. In 60% of GSD Ia patients we found abnormal results, with a decrease of VWF:Ag and multimer analysis showing reduced intensity of individual oligomers in the presence of all multimers with a normal triplet structure. We interpret these findings as an acquired 'von Willebrand syndrome type I' in GSD Ia. The underlying metabolic mechanism and a potential role in the protection from vascular complication still needs to be evaluated.

Hyperchylomicronaemia due to lipoprotein lipase deficiency as a cause of false-positive newborn screening for biotinidase deficiency

Two cases of molecular genetically proven lipoprotein lipase deficiency are reported. Both patients were detected owing to a false-positive neonatal screening test for biotinidase deficiency. We conclude that both the fluorimetric and the colorimetric screening tests for biotinidase deficiency used with dried blood samples are affected by severe hyperchylomicronaemia and that, most probably, severe plasma turbidity interferes with the assay.

A new fluorimetric enzyme assay for the diagnosis of Niemann-Pick A/B, with specificity of natural sphingomyelinase substrate

6-Hexadecanoylamino-4-methylumbelliferylphosphorylcholine (HMUPC) was shown to be a specific substrate for the determination of acid (lysosomal) sphingomyelinase (ASM; gene SMPD1). Fibroblasts (n = 27) and leukocytes (n = 8) from both the A and B types of Niemann-Pick disease showed < 6% and < 10% of mean normal ASM activity, respectively. Niemann-Pick A or B patients bearing the Q292K mutation had apparently normal ASM activity with our new artificial substrate. These patients with false-normal sphingomyelinase activity, however, could readily be detected by determining the extent of inhibition of enzymatic hydrolysis of the artificial substrate HMU-PC by an unlabelled natural substrate, in particular lysosphingomyelin. This approach is generally applicable. Our novel assay for ASM combines the ease of a rapid and robust enzyme assay using a fluorogenic substrate with the specificity of an ASM assay using a natural substrate. Such assays are obviously more convenient to the diagnostic laboratory, since radiolabelled substrates are not required.

A novel mutation in the GLUT2 gene in a patient with Fanconi-Bickel syndrome detected by neonatal screening for galactosaemia

A patient affected by Fanconi-Bickel syndrome detected by neonatal screening for galactosaemia is reported. Molecular studies of the GLUT2 gene led to the identification of a novel mutation of the glucose transporter.

MLYCD mutation analysis: evidence for protein mistargeting as a cause of MLYCD deficiency

Malonyl-CoA decarboxylase (MLYCD) deficiency is an autosomal recessive disorder characterized by malonic aciduria, developmental delay, seizure disorder, hypoglycemia, and cardiomyopathy. Genomic sequencing of MLYCD in nine unrelated patients identified 16 of 18 pathogenic alleles, which are documented in the newly created Human MLYCD Allelic Variant Database (http://mlycd.hgu.mrc.ac.uk/). Fibroblast cell lines were available from eight of these patients and two previously reported patients with homozygous MLYCD mutations. Western blot analysis using antisera raised to a C-terminal peptide detected a 66-kDa band that was absent in six patients and substantially reduced in three patients. One patient showed an increase in protein levels with a prominent smeary 68-l83-kDa band. Immunocytochemical analysis of MLYCD-expressing patient cell lines showed apparent intracellular mislocalization. An extreme N-terminal mutation c.8G>A (p.G3D) mislocalized to the plasma membrane, suggesting that a novel targeting signal may reside in a four-amino acid conserved N-terminal motif. A 25-base deletion between the putative mitochondrial and peroxisomal initiating codons (M1 and M40) and a point mutation ablating the second of these (c.119T>C, p.M40T) both showed punctate perinuclear staining. As none of the three mislocalizing mutations are predicted to alter the catalytic function of the peptide, it seems likely that correct subcellular localization of MLYCD is critical for it to function normally.

Partial response to biotin therapy in a patient with holocarboxylase synthetase deficiency: clinical, biochemical, and molecular genetic aspects

We report the clinical course and biochemical findings of a 10-year-old, mentally retarded girl with late-onset holocarboxylase synthetase (HCS, gene symbol HLCS) deficiency and only partial response to biotin. On treatment, even with an unusually high dose of 200mg/day, activities of the biotin-dependent mitochondrial carboxylases in lymphocytes remained below 50% of the mean control values. Not only urinary 3-hydroxyisovaleric acid excretion has been persistently elevated, but also plasma and, with even higher concentrations, cerebrospinal fluid 3-hydroxyisovaleric acid have not normalized. The unusual and insufficient response of this patient to biotin treatment can be explained by the effect of the combination of the common HLCS allele IVS10 +5 g>a on one chromosome and a truncating mutation on the other. This case illustrates mechanisms involved in the genotype-phenotype correlation that unequivocally exists in HCS deficiency.

Neutrophil aggregates in a 13-year-old girl: a rare hematological phenomenon

Aggregation of neutrophils in peripheral blood smears is a very rare, mostly self-limiting phenomenon and may result in pseudoleukopenia. In the majority of cases, malignancies, infections, or hepatic disorders have been identified as the underlying condition. Although the exact reason for neutrophil aggregation in vitro has not been clarified, its relation to the use of ethylenediaminetetraacetate acid as an anticoagulant has been described in adults. We report here on the occurrence of transient neutrophil aggregation in a 13-year-old girl with Herpes simplex and concomitant Mycoplasma pneumoniae infection.

Cardiolipin deficiency in X-linked cardioskeletal myopathy and neutropenia (Barth syndrome, MIM 302060): a study in cultured skin fibroblasts

We determined cardiolipin concentrations in cultured skin fibroblasts of 5 patients with X-linked cardioskeletal myopathy and neutropenia (Barth syndrome, MIM 302060) and in two groups of control patients. High-performance liquid chromatography-electrospray mass spectrometry was used to quantify total cardiolipin and subclasses of cardiolipin molecular species in cultured skin fibroblasts. Total cardiolipin and cardiolipin subclasses were decreased in patients with Barth syndrome as compared with normal control patients and disease control patients. Patients with Barth syndrome have a specific decrease of various cardiolipin molecular species, foremost tetralineoyl-cardiolipin. Therefore the analysis of cardiolipin in fibroblasts offers a specific biochemical approach to detect this disorder.

A secondary respiratory chain defect in a patient with Fanconi-Bickel syndrome

A North African boy, the son of consanguineous parents, presented at 8 years of age with hypophosphataemic rickets due to De Toni-Debré-Fanconi syndrome. Hepatomegaly and abnormalities of carbohydrate metabolism were suggestive of Fanconi-Bickel syndrome. This was confirmed by the detection of a mutation within GLUT2, the gene encoding the liver-type facilitative glucose transporter. The study of the respiratory chain revealed a deficiency of complexes I, III and IV in muscle. Mechanisms responsible for an impairment ofmitochondrial function, which we interpret as a secondary phenomenon, are discussed.

Fanconi-Bickel syndrome--a congenital defect of facilitative glucose transport

Fanconi-Bickel syndrome (FBS, OMIM 227810) is a rare type of glycogen storage disease (GSD). It is caused by homozygous or compound heterozygous mutations within GLUT2, the gene encoding the most important facilitative glucose transporter in hepatocytes, pancreatic beta-cells, enterocytes, and renal tubular cells. To date, 112 patients have been reported in the literature. Most patients have the typical combination of clinical symptoms: hepatomegaly secondary to glycogen accumulation, glucose and galactose intolerance, fasting hypoglycemia, a characteristic tubular nephropathy, and severely stunted growth. In 63 patients, mutation analysis has revealed a total of 34 different GLUT2 mutations with none of them being particularly frequent. No specific therapy is available for FBS patients. Symptomatic treatment is directed towards a stabilization of glucose homeostasis and compensation for renal losses of various solutes. In addition to the clinical and molecular genetic aspects of FBS, this review discusses the pathophysiology of the disease and compares it to recent findings in GLUT2 deficient transgenic animals. An overview is also provided on recently discovered members of the rapidly growing family of facilitative glucose transporters, which are novel candidates for congenital disorders of carbohydrate metabolism.

Tetrahydrobiopterin responsiveness in phenylketonuria. Two new cases and a review of molecular genetic findings

We report two new patients with tetrahydrobiopterin (BH4)-responsive phenylketonuria and compare their phenylalanine hydroxylase (PAH) genotypes (A395P/ IVS12+g>a and R261Q/165T, respectively) to those of previous cases from the literature. These case observations confirm earlier reports stating that BH4-responsive patients are frequently carriers of a missense mutation within the DNA region coding for the catalytic domain of the enzyme. Interestingly, many of the PAH gene mutations detected in BH4-responsive patients have been associated with an inconsistent phenotype in the past. Our case reports confirm that it is necessary to thoroughly examine individuals with increased phenylalanine levels, not only to detect BH4 deficiency, but also to identify patients with PAH deficiency who may benefit from BH4 treatment. In both of our patients, however, an effect of BH4 (7.5 mg/kg) on plasma phenylalanine levels was not seen in the newborn period. We therefore conclude that a normal neonatal BH4 test does not necessarily exclude BH4 responsiveness in all such patients.

Laboratory signs of activated coagulation are common in Henoch-Schönlein purpura

We investigated 17 patients with Henoch-Schönlein purpura (HSP) and describe as yet unreported abnormal results of blood coagulation tests. In parallel to the activity of the disease, D-dimer concentrations in plasma were found to be significantly increased in 15 of the 17 patients; almost 50% of all patients showed values higher than 10 times the upper limit of the normal range. In 11 patients, plasma concentrations of thrombin-antithrombin complex (TAT) and prothrombin fragments 1 and 2 (F1+2) were examined; six of them showed abnormal results. The pathologic values were correlated to the activity of the disease, but abnormalities were also found in milder cases of HSP. These findings probably reflect local reactions within inflamed blood vessels rather than a systemic activation of coagulation and hyperfibrinolysis. Clinicians should be aware of these laboratory findings in order not to confuse common cases of HSP with purpura necroticans, a very severe type of vasculitis in which signs of disseminated intravascular coagulation (DIC) have been reported. Our findings suggest that an activation of coagulation including hyperfibrinolysis secondary to the endothelial damage is a typical feature of the common types of HSP.

Hyperinsulinism in syndromal disorders

Analysis of a German database comprising a total of 54 patients with neonatal manifestations of persistent hyperinsulinism revealed 5 patients in whom hyperinsulinism was associated with additional clinical symptoms, suggesting an underlying syndromal disorder. Three of the patients presented with a similar yet unknown clinical entity characterized by severe psychomotor retardation, chronic pulmonary disease, hypothyroidism and congenital heart defects. A fourth patient was affected by severe congenital central hypoventilation syndrome. The fifth patient presented with Beckwith-Wiedemann syndrome, with unusually severe and persistent hyperinsulinism requiring subtotal pancreatectomy.

CONCLUSION

Our results indicate that, in addition to the well-known biochemical pathways, more complex pathophysiological mechanisms can result in persistent hyperinsulinism that presents clinically with a disease involving multiple organs.

Operational Remote Sensing of Aerosols over Land to Account for Directional Effects

The assumption that the ground is a Lambertian reflector is commonly adopted in operational atmospheric corrections of spaceborne sensors. Through a simple modeling of directional effects in radiative transfer following the second simulation of the satellite signal in the solar spectrum (6S) approach, we propose an operational method to account for the departure from Lambertian behavior of a reflector covered by a scattering medium. This method relies on the computation of coupling terms between the reflecting and the scattering media and is able to deal with a two-layer atmosphere. We focus on the difficult problem of aerosol remote sensing over land. One popular sensing method relies on observations over dense dark vegetation, for which the surface reflectance is low and quite well defined in the blue and in the red. Therefore a study was made for three cases: (1) dark vegetation covered by atmospheric aerosols, (2) atmospheric aerosols covered by molecules, and finally (3) dark vegetation covered by atmospheric aerosols covered by molecules. Comparisons of top-of-the-atmosphere reflectances computed with our modeling and reference computations made with the successive-order-of-scattering code show the robustness of the modeling in the blue and in the red for aerosol optical thicknesses as great as 0.6 and solar zenith angles as large as 60 degrees . The model begins to fail only in the blue for large solar zenith angles. The benefits expected for aerosol remote sensing over land are evaluated with an aerosol retrieval scheme developed for the Medium-Resolution Imaging Spectrometer. The main result is a better constraint on the aerosol model with inclusion of directional effects and a weaker effect on the optical thickness of the retrieved aerosol. The directional scheme is then applied to the aerosol remote-sensing problem in actual Indian Remote Sensing Satellite P3/Modular Optoelectronic Scanner images over land and shows significant improvement compared with a Lambertian algorithm. Moreover, it confirms our main theoretical conclusion.

Radiative transfer model for the computation of radiance and polarization in an ocean-atmosphere system: polarization properties of suspended matter for remote sensing

A radiative transfer code termed OSOA for the ocean-atmosphere system that is able to predict the total and the polarized signals has been developed. The successive-orders-of-scattering method is used. The air-water interface is modeled as a planar mirror. Four components grouped by their optical properties, pure seawater, phytoplankton, nonchlorophyllose matter, and yellow substances, are included in the water column. Models are validated through comparisons with standard models. The numerical accuracy of the method is better than 2%; high computational efficiency is maintained. The model is used to study the influence of polarization on the detection of suspended matter. Polarizing properties of hydrosols are discussed: phytoplankton cells exhibit weak polarization and small inorganic particles, which are strong backscatterers, contribute appreciably to the polarized signal. Therefore the use of the polarized signal to extract the sediment signature promises good results. Also, polarized radiance could improve characterization of aerosols when open ocean waters are treated.

Molecular genetic basis and prevalence of glycogen storage disease type IIIA in the Faroe Islands

Glycogen storage disease type IIIA (GSD IIIA) is caused by mutations of the amyloglucosidase gene (AGL). For most populations, none of the AGL mutations described to date is particularly frequent. In this paper, we report that six children with GSD IIIA from the Faroe Islands were found to be homozygous for the novel nonsense mutation c.1222C>T (R408X) of the AGL gene. This mutation is easily detected by restriction enzyme digest with NsiI after mismatch PCR. Investigating five intragenic polymorphisms, we could show that this mutation was always associated with the same haplotype. The c.1222C>T mutation could be detected on two chromosomes of another 50 unselected GSD IIIA patients of other European or North American origin which means that this mutation plays a minor role worldwide. From the fact that we are currently aware of a total of 14 GSD IIIA cases in the Faroese population of 45 000, the observed prevalence is 1 : 3100. While the novel AGL mutation c.1222C>T was not detectable among 198 German newborns, nine out of 272 children from the Faroese neonatal screening program were found to be heterozygous for this mutation. Thus, the calculated prevalence is 1 : 3600 (95% CI 1:700-1:6400). We conclude that due to a founder effect, the Faroe Islands have the highest prevalence of GSD IIIA world-wide. The detection of the molecular defect has facilitated the diagnosis and has offered the opportunity for prenatal diagnosis in this patient group.

Letting the cat out of the bag

The image of the cheetah sprinting gracefully across the African Serengeti in pursuit of its prey is one that we're all familiar with. Many people perceive the cheetah as an animal flawlessly adapted to its environment-the perfect predator.