Genetic landscape of pediatric acute liver failure of indeterminate origin

BACKGROUND AND AIMS

Pediatric acute liver failure (PALF) is a life-threatening condition. In Europe, the main causes are viral infections (12%-16%) and inherited metabolic diseases (14%-28%). Yet, in up to 50% of cases the underlying etiology remains elusive, challenging clinical management, including liver transplantation. We systematically studied indeterminate PALF cases referred for genetic evaluation by whole-exome sequencing (WES), and analyzed phenotypic and biochemical markers, and the diagnostic yield of WES in this condition.

APPROACH AND RESULTS

With this international, multicenter observational study, patients (0-18 y) with indeterminate PALF were analyzed by WES. Data on the clinical and biochemical phenotype were retrieved and systematically analyzed.

RESULTS

In total, 260 indeterminate PALF patients from 19 countries were recruited between 2011 and 2022, of whom 59 had recurrent PALF. WES established a genetic diagnosis in 37% of cases (97/260). Diagnostic yield was highest in children with PALF in the first year of life (41%), and in children with recurrent acute liver failure (64%). Thirty-six distinct disease genes were identified. Defects in NBAS (n=20), MPV17 (n=8), and DGUOK (n=7) were the most frequent findings. When categorizing, the most frequent were mitochondrial diseases (45%), disorders of vesicular trafficking (28%), and cytosolic aminoacyl-tRNA synthetase deficiencies (10%). One-third of patients had a fatal outcome. Fifty-six patients received liver transplantation.

CONCLUSIONS

This study elucidates a large contribution of genetic causes in PALF of indeterminate origin with an increasing spectrum of disease entities. The high proportion of diagnosed cases and potential treatment implications argue for exome or in future rapid genome sequencing in PALF diagnostics.

Impact of genetic and non-genetic factors on phenotypic diversity in NBAS-associated disease

Biallelic pathogenic variants in neuroblastoma-amplified sequence (NBAS) cause a pleiotropic multisystem disorder. Three clinical subgroups have been defined correlating with the localisation of pathogenic variants in the NBAS gene: variants affecting the C-terminal region of NBAS result in SOPH syndrome (short stature, optic atrophy, Pelger-Huët anomaly), variants affecting the Sec 39 domain are associated with infantile liver failure syndrome type 2 (ILFS2) and variants affecting the ß-propeller domain give rise to a combined phenotype. However, there is still unexplained phenotypic diversity across the three subgroups, challenging the current concept of genotype-phenotype correlations in NBAS-associated disease. Therefore, besides examining the genetic influence, we aim to elucidate the potential impact of pre-symptomatic diagnosis, emergency management and other modifying variables on the clinical phenotype. We investigated genotype-phenotype correlations in individuals sharing the same genotypes (n = 30 individuals), and in those sharing the same missense variants with a loss-of-function variant in trans (n = 38 individuals). Effects of a pre-symptomatic diagnosis and emergency management on the severity of acute liver failure (ALF) episodes also were analysed, comparing liver function tests (ALAT, ASAT, INR) and mortality. A strong genotype-phenotype correlation was demonstrated in individuals sharing the same genotype; this was especially true for the ILFS2 subgroup. Genotype-phenotype correlation in patients sharing only one missense variant was still high, though at a lower level. Pre-symptomatic diagnosis in combination with an emergency management protocol leads to a trend of reduced severity of ALF. High genetic impact on clinical phenotype in NBAS-associated disease facilitates monitoring and management of affected patients sharing the same genotype. Pre-symptomatic diagnosis and an emergency management protocol do not prevent ALF but may reduce its clinical severity.

De novo variants in RNF213 are associated with a clinical spectrum ranging from Leigh syndrome to early-onset stroke

PURPOSE

RNF213, encoding a giant E3 ubiquitin ligase, has been recognized for its role as a key susceptibility gene for moyamoya disease. Case reports have also implicated specific variants in RNF213 with an early-onset form of moyamoya disease with full penetrance. We aimed to expand the phenotypic spectrum of monogenic RNF213-related disease and to evaluate genotype-phenotype correlations.

METHODS

Patients were identified through reanalysis of exome sequencing data of an unselected cohort of unsolved pediatric cases and through GeneMatcher or ClinVar. Functional characterization was done by proteomics analysis and oxidative phosphorylation enzyme activities using patient-derived fibroblasts.

RESULTS

We identified 14 individuals from 13 unrelated families with (de novo) missense variants in RNF213 clustering within or around the Really Interesting New Gene (RING) domain. Individuals presented either with early-onset stroke (n = 11) or with Leigh syndrome (n = 3). No genotype-phenotype correlation could be established. Proteomics using patient-derived fibroblasts revealed no significant differences between clinical subgroups. 3D modeling revealed a clustering of missense variants in the tertiary structure of RNF213 potentially affecting zinc-binding suggesting a gain-of-function or dominant negative effect.

CONCLUSION

De novo missense variants in RNF213 clustering in the E3 RING or other regions affecting zinc-binding lead to an early-onset syndrome characterized by stroke or Leigh syndrome.

Genetics of Pediatric Epilepsy: Next-Generation Sequencing in Clinical Practice

Epilepsy is one of the most common neurological disorders with diverse phenotypic characteristics and high genetic heterogeneity. Epilepsy often occurs in childhood, so timely diagnosis and adequate therapy are crucial for preserving quality of life and unhindered development of a child. Next-generation-sequencing (NGS)-based tools have shown potential in increasing diagnostic yield. The primary objective of this study was to evaluate the impact of genetic testing and to investigate the diagnostic utility of targeted gene panel sequencing. This retrospective cohort study included 277 patients aged 6 months to 17 years undergoing NGS with an epilepsy panel covering 142 genes. Of 118 variants detected, 38 (32.2%) were not described in the literature. We identified 64 pathogenic or likely pathogenic variants with an overall diagnostic yield of 23.1%. We showed a significantly higher diagnostic yield in patients with developmental delay (28.9%). Furthermore, we showed that patients with variants reported as pathogenic presented with seizures at a younger age, which led to the conclusion that such children should be included in genomic diagnostic procedures as soon as possible to achieve a correct diagnosis in a timely manner, potentially leading to better treatment and avoidance of unnecessary procedures. Describing and discovering the genetic background of the disease not only leads to a better understanding of the mechanisms of the disorder but also opens the possibility of more precise and individualized treatment based on stratified medicine.

A biallelic loss-of-function variant in MYZAP is associated with a recessive form of severe dilated cardiomyopathy

PURPOSE

Dilated cardiomyopathy (DCM) is a primary disorder of the cardiac muscle, characterised by dilatation of the left ventricle and contractile dysfunction. About 50% of DCM cases can be attributed to monogenic causes, whereas the aetiology in the remaining patients remains unexplained.

METHODS

We report a family with two brothers affected by severe DCM with onset in the adolescent period. Using exome sequencing, we identified a homozygous premature termination variant in the MYZAP gene in both affected sibs. MYZAP encodes for myocardial zonula adherens protein - a conserved cardiac protein in the intercalated disc structure of cardiomyocytes.

RESULTS

The effect of the variant was demonstrated by light and electron microscopy of the heart muscle and immunohistochemical and Western blot analysis of MYZAP protein in the heart tissue of the proband. Functional characterization using patient-derived induced pluripotent stem cell cardiomyocytes revealed significantly lower force and longer time to peak contraction and relaxation consistent with severe contractile dysfunction.

CONCLUSION

We provide independent support for the role of biallelic loss-of-function MYZAP variants in dilated cardiomyopathy. This report extends the spectrum of cardiac disease associated with dysfunction of cardiac intercalated disc junction and sheds light on the mechanisms leading to DCM.

NBAS Variants Are Associated with Quantitative and Qualitative NK and B Cell Deficiency

PURPOSE

Biallelic pathogenic NBAS variants manifest as a multisystem disorder with heterogeneous clinical phenotypes such as recurrent acute liver failure, growth retardation, and susceptibility to infections. This study explores how NBAS-associated disease affects cells of the innate and adaptive immune system.

METHODS

Clinical and laboratory parameters were combined with functional multi-parametric immunophenotyping methods in fifteen NBAS-deficient patients to discover possible alterations in their immune system.

RESULTS

Our study revealed reduced absolute numbers of mature CD56dim natural killer (NK) cells. Notably, the residual NK cell population in NBAS-deficient patients exerted a lower potential for activation and degranulation in response to K562 target cells, suggesting an NK cell-intrinsic role for NBAS in the release of cytotoxic granules. NBAS-deficient NK cell activation and degranulation was normalized upon pre-activation by IL-2 in vitro, suggesting that functional impairment was reversible. In addition, we observed a reduced number of naïve B cells in the peripheral blood associated with hypogammaglobulinemia.

CONCLUSION

In summary, we demonstrate that pathogenic biallelic variants in NBAS are associated with dysfunctional NK cells as well as impaired adaptive humoral immunity.

Current Status of Newborn Screening in Southeastern Europe

Significant part of Southeastern Europe (with a population of 76 million) has newborn screening (NBS) programs non-harmonized with developed European countries. Initial survey was conducted in 2013/2014 among 11 countries from the region (Albania, Bulgaria, Bosnia and Herzegovina (BIH), Croatia, Kosovo, Macedonia, Moldova, Montenegro, Romania, Serbia, and Slovenia) to assess the main characteristics of their NBS programs and their future plans. Their cumulative population at that time was ~52,5 million. At that time, none of the countries had an expanded NBS program, while phenylketonuria screening was not introduced in four and congenital hypothyroidism in three of 11 countries. We repeated the survey in 2020 inviting the same 11 countries, adding Cyprus, Greece, Hungary, and Malta (due to their geographical position in the wider region). The aims were to assess the current state, to evaluate the change in the period, and to identify the main obstacles impacting the implementation of expanded NBS and/or reaching a wider population. Responses were collected from 12 countries (BIH-Federation of BIH, BIH-Republic of Srpska, Bulgaria, Croatia, Greece, Hungary, Kosovo, North Macedonia, Malta, Montenegro, Romania, Serbia, Slovenia) with a population of 68.5 million. The results of the survey showed that the regional situation regarding NBS only modestly improved in this period. All of the surveyed countries except Kosovo screened for at least congenital hypothyroidism, while phenylketonuria was not screened in four of 12 countries. Croatia and Slovenia implemented an expanded NBS program using tandem mass spectrometry from the time of last survey. In conclusion, the current status of NBS programs in Southeastern Europe is very variable and is still underdeveloped (or even non-existent) in some of the countries. We suggest establishing an international task-force to assist with implementation and harmonization of basic NBS services where needed.

Genotype-phenotype correlation in 44 Czech, Slovak, Croatian and Serbian patients with mucopolysaccharidosis type II

Mucopolysaccharidosis type II (Hunter syndrome, MPS II, OMIM 309900) is an X-linked lysosomal storage disorder caused by deficiency of iduronate-2-sulfatase (IDS). We analyzed clinical and laboratory data from 44 Slavic patients with this disease. In total, 21 Czech, 7 Slovak, 9 Croatian and 7 Serbian patients (43 M/1 F) were included in the study (median age 11.0 years, range 1.2-43 years). Birth prevalence ranged from 1:69,223 (Serbia) to 1:192,626 (Czech Rep.). In the majority of patients (71%), the disease manifested in infancy. Cognitive functions were normal in 10 patients. Four, six and 24 patients had mild, moderate, and severe developmental delay, respectively, typically subsequent to developmental regression (59%). Residual enzyme activity showed no predictive value, and estimation of glycosaminoglycans (GAGs) had only limited importance for prognosis. Mutation analysis performed in 36 families led to the identification of 12 novel mutations, eight of which were small deletions/insertions. Large deletions/rearrangements and all but one small deletion/insertion led to a severe phenotype. This genotype-phenotype correlation was also identified in six cases with recurrent missense mutations. Based on patient genotype, the severity of the disease may be predicted with high probability in approximately half of MPS II patients.

NAXE Mutations Disrupt the Cellular NAD(P)HX Repair System and Cause a Lethal Neurometabolic Disorder of Early Childhood

To safeguard the cell from the accumulation of potentially harmful metabolic intermediates, specific repair mechanisms have evolved. APOA1BP, now renamed NAXE, encodes an epimerase essential in the cellular metabolite repair for NADHX and NADPHX. The enzyme catalyzes the epimerization of NAD(P)HX, thereby avoiding the accumulation of toxic metabolites. The clinical importance of the NAD(P)HX repair system has been unknown. Exome sequencing revealed pathogenic biallelic mutations in NAXE in children from four families with (sub-) acute-onset ataxia, cerebellar edema, spinal myelopathy, and skin lesions. Lactate was elevated in cerebrospinal fluid of all affected individuals. Disease onset was during the second year of life and clinical signs as well as episodes of deterioration were triggered by febrile infections. Disease course was rapidly progressive, leading to coma, global brain atrophy, and finally to death in all affected individuals. NAXE levels were undetectable in fibroblasts from affected individuals of two families. In these fibroblasts we measured highly elevated concentrations of the toxic metabolite cyclic-NADHX, confirming a deficiency of the mitochondrial NAD(P)HX repair system. Finally, NAD or nicotinic acid (vitamin B3) supplementation might have therapeutic implications for this fatal disorder.

Recurrent acute liver failure due to NBAS deficiency: phenotypic spectrum, disease mechanisms, and therapeutic concepts

BACKGROUND

Acute liver failure (ALF) in infancy and childhood is a life-threatening emergency and in about 50% the etiology remains unknown. Recently biallelic mutations in NBAS were identified as a new molecular cause of ALF with onset in infancy, leading to recurrent acute liver failure (RALF).

METHODS

The phenotype and medical history of 14 individuals with NBAS deficiency was studied in detail and functional studies were performed on patients' fibroblasts.

RESULTS

The phenotypic spectrum of NBAS deficiency ranges from isolated RALF to a multisystemic disease with short stature, skeletal dysplasia, immunological abnormalities, optic atrophy, and normal motor and cognitive development resembling SOPH syndrome. Liver crises are triggered by febrile infections; they become less frequent with age but are not restricted to childhood. Complete recovery is typical, but ALF crises can be fatal. Antipyretic therapy and induction of anabolism including glucose and parenteral lipids effectively ameliorates the course of liver crises. Patients' fibroblasts showed an increased sensitivity to high temperature at protein and functional level and a disturbed tethering of vesicles, pointing at a defect of intracellular transport between the endoplasmic reticulum and Golgi.

CONCLUSIONS

Mutations in NBAS cause a complex disease with a wide clinical spectrum ranging from isolated RALF to a multisystemic phenotype. Thermal susceptibility of the syntaxin 18 complex is the basis of fever dependency of ALF episodes. NBAS deficiency is the first disease related to a primary defect of retrograde transport. Identification of NBAS deficiency allows optimized therapy of liver crises and even prevention of further episodes.

Biallelic Mutations in NBAS Cause Recurrent Acute Liver Failure with Onset in Infancy

Acute liver failure (ALF) in infancy and childhood is a life-threatening emergency. Few conditions are known to cause recurrent acute liver failure (RALF), and in about 50% of cases, the underlying molecular cause remains unresolved. Exome sequencing in five unrelated individuals with fever-dependent RALF revealed biallelic mutations in NBAS. Subsequent Sanger sequencing of NBAS in 15 additional unrelated individuals with RALF or ALF identified compound heterozygous mutations in an additional six individuals from five families. Immunoblot analysis of mutant fibroblasts showed reduced protein levels of NBAS and its proposed interaction partner p31, both involved in retrograde transport between endoplasmic reticulum and Golgi. We recommend NBAS analysis in individuals with acute infantile liver failure, especially if triggered by fever.

Respiratory chain deficiency in nonmitochondrial disease

OBJECTIVE

In this study, we report 5 patients with heterogeneous phenotypes and biochemical evidence of respiratory chain (RC) deficiency; however, the molecular diagnosis is not mitochondrial disease.

METHODS

The reported patients were identified from a cohort of 60 patients in whom RC enzyme deficiency suggested mitochondrial disease and underwent whole-exome sequencing.

RESULTS

Five patients had disease-causing variants in nonmitochondrial disease genes ORAI1, CAPN3, COLQ, EXOSC8, and ANO10, which would have been missed on targeted next-generation panels or on MitoExome analysis.

CONCLUSIONS

Our data demonstrate that RC abnormalities may be secondary to various cellular processes, including calcium metabolism, neuromuscular transmission, and abnormal messenger RNA degradation.

Phenylketonuria screening and management in southeastern Europe - survey results from 11 countries

BACKGROUND

We aimed to assess the current state of PKU screening and management in the region of southeastern Europe.

METHODS

A survey was performed involving all identified professionals responsible for the PKU management in the 11 countries from South-Eastern region of Europe (Albania, Bulgaria, Bosnia and Herzegovina, Croatia, Kosovo, Macedonia, Moldova, Montenegro, Romania, Serbia, Slovenia). The questionnaire was designed to assess the characteristics regarding PKU management in three main areas: nation-wide characteristics, PKU screening, and characteristics of the PKU management in the responding centre. It consisted of 56 questions. The distribution and collection of the questionnaires (via e-mail) was taking place from December 2013 to March 2014.

RESULTS

Responses from participants from 11 countries were included; the countries cumulative population is approx. 52.5 mio. PKU screening was not yet introduced in 4 of 11 countries. Reported PKU incidences ranged from 1/7325 to 1/39338 (and were not known for 5 countries). National PKU guidelines existed in 5 of 11 countries and 7 of 11 countries had PKU registry (registries included 40 to 194 patients). The number of PKU centers in each country varied from 1 to 6. Routine genetic diagnostics was reported in 4 of 11 countries. Most commonly used laboratory method to assess phenylalanine levels was fluorometric. Tetrahydrobiopterine was used in only 2 of 11 countries. Most frequently, pediatricians were caring for the patients. Dietitian was a member of PKU team in only 4 of 11 countries, while regular psychological assessments were performed in 6 of 11 countries. Patient's PKU society existed in 7 of 11 countries.

CONCLUSIONS

The region of southeastern Europe was facing certain important challenges of PKU screening and management. Neonatal PKU screening should be introduced throughout the region. Furthermore, PKU management was falling behind internationally established standards-of-care in many aspects.

Newborn screening in southeastern Europe

The aim of our study was to assess the current state of newborn screening (NBS) in the region of southeastern Europe, as an example of a developing region, focusing also on future plans. Responses were obtained from 11 countries. Phenylketonuria screening was not introduced in four of 11 countries, while congenital hypothyroidism screening was not introduced in three of them; extended NBS programs were non-existent. The primary challenges were identified. Implementation of NBS to developing countries worldwide should be considered as a priority.

Use of whole-exome sequencing to determine the genetic basis of multiple mitochondrial respiratory chain complex deficiencies

IMPORTANCE

Mitochondrial disorders have emerged as a common cause of inherited disease, but their diagnosis remains challenging. Multiple respiratory chain complex defects are particularly difficult to diagnose at the molecular level because of the massive number of nuclear genes potentially involved in intramitochondrial protein synthesis, with many not yet linked to human disease.

OBJECTIVE

To determine the molecular basis of multiple respiratory chain complex deficiencies.

DESIGN, SETTING, AND PARTICIPANTS

We studied 53 patients referred to 2 national centers in the United Kingdom and Germany between 2005 and 2012. All had biochemical evidence of multiple respiratory chain complex defects but no primary pathogenic mitochondrial DNA mutation. Whole-exome sequencing was performed using 62-Mb exome enrichment, followed by variant prioritization using bioinformatic prediction tools, variant validation by Sanger sequencing, and segregation of the variant with the disease phenotype in the family.

RESULTS

Presumptive causal variants were identified in 28 patients (53%; 95% CI, 39%-67%) and possible causal variants were identified in 4 (8%; 95% CI, 2%-18%). Together these accounted for 32 patients (60% 95% CI, 46%-74%) and involved 18 different genes. These included recurrent mutations in RMND1, AARS2, and MTO1, each on a haplotype background consistent with a shared founder allele, and potential novel mutations in 4 possible mitochondrial disease genes (VARS2, GARS, FLAD1, and PTCD1). Distinguishing clinical features included deafness and renal involvement associated with RMND1 and cardiomyopathy with AARS2 and MTO1. However, atypical clinical features were present in some patients, including normal liver function and Leigh syndrome (subacute necrotizing encephalomyelopathy) seen in association with TRMU mutations and no cardiomyopathy with founder SCO2 mutations. It was not possible to confidently identify the underlying genetic basis in 21 patients (40%; 95% CI, 26%-54%).

CONCLUSIONS AND RELEVANCE

Exome sequencing enhances the ability to identify potential nuclear gene mutations in patients with biochemically defined defects affecting multiple mitochondrial respiratory chain complexes. Additional study is required in independent patient populations to determine the utility of this approach in comparison with traditional diagnostic methods.

Diversity of approaches to classic galactosemia around the world: a comparison of diagnosis, intervention, and outcomes

Without intervention, classic galactosemia is a potentially fatal disorder in infancy. With the benefit of early diagnosis and dietary restriction of galactose, the acute sequelae of classic galactosemia can be prevented or reversed. However, despite early and lifelong dietary treatment, many galactosemic patients go on to experience serious long-term complications including cognitive disability, speech problems, neurological and/or movement disorders and, in girls and women, ovarian dysfunction. Further, there remains uncertainty surrounding what constitutes a 'best practice' for treating this disorder. To explore the extent and implications of this uncertainty, we conducted a small but global survey of healthcare providers who follow patients with classic galactosemia, seeking to compare established protocols for diagnosis, intervention, and follow-up, as well as the outcomes and outcome frequencies seen in the patient populations cared for by these providers. We received 13 survey responses representing five continents and 11 countries. Respondents underscored disparities in approaches to diagnosis, management and follow-up care. Notably, we saw no clear relationship between differing approaches to care and long-term outcomes in the populations studied. Negative outcomes occurred in the majority of cases regardless of when treatment was initiated, how tightly galactose intake was restricted, or how closely patients were monitored. We document here what is, to our knowledge, the first global comparison of healthcare approaches to classic galactosemia. These data reinforce the idea that there is currently no one best practice for treating patients with classic galactosemia, and underscore the need for more extensive and statistically powerful comparative studies to reveal potential positive or negative impacts of differing approaches.

Plasma biomarker identification in S-adenosylhomocysteine hydrolase deficiency

S-Adenosylhomocysteine hydrolase (AHCY) deficiency is a rare congenital disorder in methionine metabolism clinically characterized by white matter atrophy, delayed myelination, slowly progressive myopathy, retarded psychomotor development and mildly active chronic hepatitis. In the present study, we utilized a comparative proteomics strategy based on 2-DE/MALDI-MS and LC/ESI-MS to analyze plasma proteins from three AHCY-deficient patients prior to and after receiving dietary treatment designed to alleviate disease symptoms. Obtained results revealed candidate biomarkers for the detection of myopathy specifically associated with AHCY deficiency, such as carbonic anhydrase 3, creatine kinase, and thrombospondin 4. Several proteins mediating T-cell activation and function were identified as well, including attractin and diacylglycerol kinase α. Further validation and functional analysis of identified proteins with clinical value would ensure that these biomarkers make their way into routine diagnosis and management of AHCY deficiency.

An overview of L-2-hydroxyglutarate dehydrogenase gene (L2HGDH) variants: a genotype-phenotype study

L-2-Hydroxyglutaric aciduria (L2HGA) is a rare, neurometabolic disorder with an autosomal recessive mode of inheritance. Affected individuals only have neurological manifestations, including psychomotor retardation, cerebellar ataxia, and more variably macrocephaly, or epilepsy. The diagnosis of L2HGA can be made based on magnetic resonance imaging (MRI), biochemical analysis, and mutational analysis of L2HGDH. About 200 patients with elevated concentrations of 2-hydroxyglutarate (2HG) in the urine were referred for chiral determination of 2HG and L2HGDH mutational analysis. All patients with increased L2HG (n=106; 83 families) were included. Clinical information on 61 patients was obtained via questionnaires. In 82 families the mutations were detected by direct sequence analysis and/or multiplex ligation dependent probe amplification (MLPA), including one case where MLPA was essential to detect the second allele. In another case RT-PCR followed by deep intronic sequencing was needed to detect the mutation. Thirty-five novel mutations as well as 35 reported mutations and 14 nondisease-related variants are reviewed and included in a novel Leiden Open source Variation Database (LOVD) for L2HGDH variants (http://www.LOVD.nl/L2HGDH). Every user can access the database and submit variants/patients. Furthermore, we report on the phenotype, including neurological manifestations and urinary levels of L2HG, and we evaluate the phenotype-genotype relationship.

Dynamic changes of striatal and extrastriatal abnormalities in glutaric aciduria type I

In glutaric aciduria type I, an autosomal recessive disease of mitochondrial lysine, hydroxylysine and tryptophan catabolism, striatal lesions are characteristically induced by acute encephalopathic crises during a finite period of brain development (age 3-36 months). The frequency of striatal injury is significantly less in patients diagnosed as asymptomatic newborns by newborn screening. Most previous studies have focused on the onset and mechanism of striatal injury, whereas little is known about neuroradiological abnormalities in pre-symptomatically diagnosed patients and about dynamic changes of extrastriatal abnormalities. Thus, the major aim of the present retrospective study was to improve our understanding of striatal and extrastriatal abnormalities in affected individuals including those diagnosed by newborn screening. To this end, we systematically analysed magnetic resonance imagings (MRIs) in 38 patients with glutaric aciduria type I diagnosed before or after the manifestation of neurological symptoms. To identify brain regions that are susceptible to cerebral injury during acute encephalopathic crises, we compared the frequency of magnetic resonance abnormalities in patients with and without such crises. Major specific changes after encephalopathic crises were found in the putamen (P < 0.001), nucleus caudatus (P < 0.001), globus pallidus (P = 0.012) and ventricles (P = 0.001). Analysis of empirical cumulative distribution frequencies, however, demonstrated that isolated pallidal abnormalities did not significantly differ over time in both groups (P = 0.544) suggesting that isolated pallidal abnormalities are not induced by acute crises--in contrast to striatal abnormalities. The manifestation of motor disability was associated with signal abnormalities in putamen, caudate, pallidum and ventricles. In addition, we found a large number of extrastriatal abnormalities in patients with and without preceding encephalophatic crises. These abnormalities include widening of anterior temporal and sylvian CSF spaces, pseudocysts, signal changes of substantia nigra, nucleus dentatus, thalamus, tractus tegmentalis centralis and supratentorial white matter as well as signs of delayed maturation (myelination and gyral pattern). In contrast to the striatum, extrastriatal abnormalities were variable and could regress or even normalize with time. This includes widening of sylvian fissures, delayed maturation, pallidal signal changes and pseudocysts. Based on these results, we hypothesize that neuroradiological abnormalities and neurological symptoms in glutaric aciduria type I can be explained by overlaying episodes of cerebral alterations including maturational delay of the brain in utero, acute striatal injury during a vulnerable period in infancy and chronic progressive changes that may continue lifelong. This may have widespread consequences for the pathophysiological understanding of this disease, long-term outcomes and therapeutic considerations.

Studies of S-adenosylhomocysteine-hydrolase polymorphism in a Croatian population

Recently, a proven case of human S-adenosylhomocysteine-hydrolase (SAHH) deficiency was reported in a Croatian boy. As molecular analysis of the SAHH gene in this case revealed two different mutant alleles, we investigated the polymorphism of human SAHH in a total of 237 red blood samples from unrelated Croats using starch gel electrophoresis and an enzyme-specific staining procedure. From the relative enzymatic activity of SAHH--determined by densitometric assessment of electrophoretic patterns, and calculated on the basis of the protein concentration of the red blood cells-we detected three individuals as being heterozygous for an SAHH 0-allele. Moreover, a total of four different electromorphic SAHHs have been observed, giving allele frequencies calculated as SAHH 1 = 0.941, SAHH 2 = 0.032, SAHH 3 = 0.006, SAHH 4 = 0.015, and SAHH 0 = 0.006.

Hypomyelination with atrophy of the basal ganglia and cerebellum (H-ABC). Report of a new case

Hypomyelination with atrophy of the basal ganglia and cerebellum (H-ABC) syndrome is a new neurodegenerative entity, which was first described by van der Knaap in 2002 in 7 patients aged from 2 months to 2 years. We describe a new, 42-month-old female patient who developed progressive dystonia, spasticity and oculogyric eye movements since the age of 3 months. The diagnosis was made by characteristic MRI findings including supratentorial hypomyelination and progressive atrophy of basal ganglia and cerebellum. Oculogyric eye movements have not been described in patients with H-ABC syndrome before. When compared with the normal age-related myelination patterns, the degree of hypomyelination increased progressively over the time course of 32 months, indicating arrest but not loss of myelination. The H-ABC syndrome adds to the differential diagnosis of progressive pyramidal and extrapyramidal movement disorders and to the increasing number of genetically determined hypomyelination syndromes.

OPA3 mutation screening in patients with unexplained 3-methylglutaconic aciduria

We have screened 13 patients with neurological abnormalities and 3-methylglutaconic aciduria (3MGA) for mutations in the OPA3 gene, which are known to be the cause of Costeff syndrome (optic atrophy, chorea and spasticity; type III 3MGA). We aimed to explore whether mutations in the OPA3 gene are present in patients with 3MGA but without classic Costeff syndrome. OPA3 mutations (IVS1-1G>C) were identified in 2 patients with the classic phenotype of type III 3MGA, but not in the other 11 patients with differing non-Costeff phenotypes associated with developmental delay and neurological signs and symptoms as described. We identified a previously described sequence variation in the OPA3 gene (c.231T>C) in 12/13 patients. The alteration was homozygous in 8/12 and heterozygous in 4/12. This alteration was also found in 60 of 98 normal control alleles. In a single patient, a novel sequence variation in the 5' UTR was identified, (c.-38A>G). Our studies suggest that the c.231T>C sequence variation is of no clinical significance, whereas the significance of the 5' UTR sequence variation remains open to speculation. Our study of the OPA3 gene in patients with 3MGA without Costeff syndrome suggests that mutations in OPA3 are not a common cause of 3MGA in the absence of signs of Costeff syndrome.

S-adenosylhomocysteine hydrolase deficiency in a human: a genetic disorder of methionine metabolism

We report studies of a Croatian boy, a proven case of human S-adenosylhomocysteine (AdoHcy) hydrolase deficiency. Psychomotor development was slow until his fifth month; thereafter, virtually absent until treatment was started. He had marked hypotonia with elevated serum creatine kinase and transaminases, prolonged prothrombin time and low albumin. Electron microscopy of muscle showed numerous abnormal myelin figures; liver biopsy showed mild hepatitis with sparse rough endoplasmic reticulum. Brain MRI at 12.7 months revealed white matter atrophy and abnormally slow myelination. Hypermethioninemia was present in the initial metabolic study at age 8 months, and persisted (up to 784 microM) without tyrosine elevation. Plasma total homocysteine was very slightly elevated for an infant to 14.5-15.9 microM. In plasma, S-adenosylmethionine was 30-fold and AdoHcy 150-fold elevated. Activity of AdoHcy hydrolase was approximately equal to 3% of control in liver and was 5-10% of the control values in red blood cells and cultured fibroblasts. We found no evidence of a soluble inhibitor of the enzyme in extracts of the patient's cultured fibroblasts. Additional pretreatment abnormalities in plasma included low concentrations of phosphatidylcholine and choline, with elevations of guanidinoacetate, betaine, dimethylglycine, and cystathionine. Leukocyte DNA was hypermethylated. Gene analysis revealed two mutations in exon 4: a maternally derived stop codon, and a paternally derived missense mutation. We discuss reasons for biochemical abnormalities and pathophysiological aspects of AdoHcy hydrolase deficiency.

Glutaryl-CoA dehydrogenase deficiency: region-specific analysis of organic acids and acylcarnitines in post mortem brain predicts vulnerability of the putamen

The neurometabolic disorder glutaryl-CoA dehydrogenase (GCDH) deficiency is biochemically characterised by an accumulation of the marker metabolites 3-hydroxyglutaric acid, glutaric acid, and glutarylcarnitine. If untreated, the disease is complicated by acute encephalopathic crises, resulting in neurodegeneration of vulnerable brain regions, in particular the putamen. 3-hydroxyglutaric acid is considered the major neurotoxin in this disease. There are only preliminary data concerning glutaric acid concentrations in the brains of affected children and the distribution of 3-hydroxyglutaric acid and glutarylcarnitine has not been described. In the present study, we investigated post mortem the distribution of 3-hydroxyglutaric and glutaric acids as well as glutarylcarnitine in 14 different brain regions, internal organs, and body fluids (urine, plasma, cerebrospinal fluid) in a 14-year-old boy. 3-Hydroxyglutaric acid showed the highest concentration (62 nmol/g protein) in the putamen among all brain areas investigated. The glutarylcarnitine concentration was also highest in the putamen (7.1 nmol/g protein). We suggest that the regional-specific differences in the relative concentrations of 3-hydroxyglutaric acid contribute to the pattern of neuronal damage in this disease. These results provide an explanatory basis for the high vulnerability of the putamen in this disease, adding to the strong corticostriatal glutamatergic input into the putamen and the high excitotoxic susceptibility of neostriatal medium spiny neurons.

The molecular basis of phenylalanine hydroxylase deficiency in Croatia

We present the results of a comprehensive analysis of mutations, polymorphisms and haplotypes in the phenylalanine hydroxylase (PAH) gene in 39 Croatian families with phenylketonuria (PKU). A total of 21 disease-causing mutations was identified on 78 out of 79 independent chromosomes. The commonest mutation, R408W on haplotype 2 was found with a relative frequency of 37 %. P281L accounted for 11 %, R261Q and E390G each for 9 % of mutant chromosomes. There were three novel mutations: L249P (c.746T>C) in exon 7, IVS8+2T>C (c.912T>C) in intron 8, and F402L (c.1206T>G) in exon 12 of the PAH gene. Two known PKU mutations were found in cis on the same chromosome in one family, highlighting the need to perform full mutation scanning in recessive disease genes for molecular diagnosis even if two known mutations have been identified in a patient. This is the first comprehensive report on PKU mutations in southeastern Europe, adding to the growing bulk of molecular data for population genetic investigations.

Stereoselective analysis of 2-hydroxysebacic acid in urine of patients with Zellweger syndrome and of premature infants fed with medium-chain triglycerides

The chiral metabolite 2-hydroxysebacic acid (2-HS) is considered to be an important diagnostic marker for peroxisomal disorders. The pathway of formation of 2-HS, excreted in increased amounts in patients with peroxisomal diseases, is not absolutely clear. Moreover, there is no information about the enantiomeric distribution of 2-HS in human urine. Here, we describe the stereodifferentiation of 2-HS in urine samples of nine patients with Zellweger syndrome (ZS), and for the first time in urine samples of premature infants fed a medium-chain triglyceride (MCT)-containing diet. Using enantioselective multidimensional gas chromatography-mass spectrometry, an increased excretion of 2R-HS was observed in all investigated ZS patients. 2-HS was also present in urine samples of premature infants fed MCT. Analogously to the ZS patients, a dominant 2R-HS excretion in the urine samples of the premature infants was identified. The formation of 2-HS is expected to result from the same or similar pathways as described for ZS patients. Additionally, we determined the absolute configuration of urinary 3-hydroxysebacic acid (3-HS) in the cases investigated. The enantioselective analysis provides further information for the diagnosis and treatment of patients with impaired peroxisomal fatty acid oxidation. Further insight into the metabolic origin and the biochemical pathway leading to these urinary metabolites is provided.

Novel OCTN2 mutations: no genotype-phenotype correlations: early carnitine therapy prevents cardiomyopathy

Primary systemic carnitine deficiency or carnitine uptake defect (OMIM 212140) is a potentially lethal, autosomal recessive disorder characterized by progressive infantile-onset cardiomyopathy, weakness, and recurrent hypoglycemic hypoketotic encephalopathy, which is highly responsive to L-carnitine therapy. Molecular analysis of the SLC22A5 (OCTN2) gene, encoding the high-affinity carnitine transporter, was done in 11 affected individuals by direct nucleotide sequencing of polymerase chain reaction products from all 10 exons. Carnitine uptake (at Km of 5 microM) in cultured skin fibroblasts ranged from 1% to 20% of normal controls. Eleven mutations (delF23, N32S, and one 11-bp duplication in exon 1; R169W in exon 3; a donor splice mutation [IVS3+1 G > A] in intron 3; frameshift mutations in exons 5 and 6; Y401X in exon 7; T440M, T468R and S470F in exon 8) are described. There was no correlation between residual uptake and severity of clinical presentation, suggesting that the wide phenotypic variability is likely related to exogenous stressors exacerbating carnitine deficiency. Most importantly, strict compliance with carnitine from birth appears to prevent the phenotype.

Gas chromatography-mass spectrometry and molecular genetic studies in families with the Conradi-Hünermann-Happle syndrome

The Conradi-Hünermann-Happle syndrome is an X-linked dominant disease that is due to mutations in the gene for emopamil binding protein. Emopamil binding protein is a Delta8-Delta7 sterol isomerase and plays a pivotal role in the final steps of cholesterol biosynthesis. We wanted to know to what extent this X-linked dominant enzyme defect has functional consequences at the biochemical level and whether it is possible to predict the clinical phenotype from serum sterol measurements. Therefore we performed sterol biochemical studies in 11 Conradi-Hünermann-Happle syndrome families and compared the results obtained to the clinical and molecular genetic findings. To assess disease severity a score considering bone and skin involvement and further features was used. For evaluation of the functional consequences we studied serum samples using gas chromatography-mass spectrometry analysis. For mutation screening we analyzed the emopamil binding protein gene using polymerase chain reaction, heteroduplex analysis of all exons, direct sequencing, and restriction enzyme analysis. Mutations in the emopamil binding protein gene were found in all 11 families including seven novel mutations affecting exons 2, 4, and 5. Gas chromatography-mass spectrometry analysis revealed markedly elevated levels of 8-dehydrocholesterol and of cholest-8(9)-en-3beta-ol and helped to identify somatic mosaicism in a clinically unaffected man. The extent of the metabolic alterations in the serum, however, do not allow prediction of the clinical phenotype, nor the genotype. This lack of correlation may be due to differences in X-inactivation between different tissues of the same patient and/or loss of the mutant clone by outgrowth of proficient clones after some time.

The mutational spectrum of human malignant autosomal recessive osteopetrosis

Human malignant infantile osteopetrosis (arOP; MIM 259700) is a genetically heterogeneous autosomal recessive disorder of bone metabolism, which, if untreated, has a fatal outcome. Our group, as well as others, have recently identified mutations in the ATP6i (TCIRG1) gene, encoding the a3 subunit of the vacuolar proton pump, which mediates the acidification of the bone/osteoclast interface, are responsible for a subset of this condition. By sequencing the ATP6i gene in arOP patients from 44 unrelated families with a worldwide distribution we have now established that ATP6i mutations are responsible for approximately 50% of patients affected by this disease. The vast majority of these mutations (40 out of 42 alleles, including seven deletions, two insertions, 10 nonsense substitutions and 21 mutations in splice sites) are predicted to cause severe abnormalities in the protein product and are likely to represent null alleles. In addition, we have also analysed nine unrelated arOP patients from Costa Rica, where this disease is apparently much more frequent than elsewhere. All nine Costa Rican patients bore either or both of two missense mutations (G405R and R444L) in amino acid residues which are evolutionarily conserved from yeast to humans. The identification of ATP6i gene mutations in two families allowed us for the first time to perform prenatal diagnosis: both fetuses were predicted not to be affected and two healthy babies were born. This study contributes to the determination of genetic heterogeneity of arOP and allows further delineation of the other genetic defects causing this severe condition.

Frequency of RET mutations in long- and short-segment Hirschsprung disease

Hirschsprung disease, or congenital aganglionic megacolon, is a genetic disorder of neural crest development affecting 1:5,000 newborns. Mutations in the RET proto-oncogene, repeatedly identified in the heterozygous state in both long- and short-segment Hirschsprung patients, lead to loss of both transforming and differentiating capacities of the activated RET through a dominant negative effect when expressed in appropriate cellular systems. The approach of single-strand conformational polymorphism analysis established for all the 20 exons of the RET proto-oncogene, and previously used to screen for point mutations in Hirschsprung patients allowed us to identify seven additional mutations among 39 sporadic and familial cases of Hirschsprung disease (detection rate 18%). This relatively low efficiency in detecting mutations of RET in Hirschsprung patients cannot be accounted by the hypothesis of genetic heterogeneity, which is not supported by the results of linkage analysis in the pedigrees analyzed so far. Almost 74% of the point mutations in our series, as well as in other patient series, were identified among long segment patients, who represented only 25% of our patient population. The finding of a C620R substitution in a patient affected with total colonic aganglionosis confirms the involvement of this mutation in the pathogenesis of different phenotypes (i.e., medullary thyroid carcinoma and Hirschsprung). Finally the R313Q mutation identified for the first time in homozygosity in a child born of consanguineous parents is associated with the most severe Hirschsprung phenotype (total colonic aganglionosis with small bowel involvement).

Sensitivity and specificity of free and total glutaric acid and 3-hydroxyglutaric acid measurements by stable-isotope dilution assays for the diagnosis of glutaric aciduria type I

Glutaric aciduria type I (GA I) is a recessive disorder caused by a deficiency of glutaryl-CoA dehydrogenase (GCDH). The biochemical hallmark of the disease is the accumulation of glutaric acid and, to a lesser degree, of 3-hydroxyglutaric acid and glutaconic acid in body fluids and tissues. A substantial number of patients show only slightly, intermittently elevated or even normal urinary excretion of glutaric acid, which makes early diagnosis and treatment to prevent the severe neurological sequelae difficult. Furthermore, elevated urinary excretion of glutaric acid can also be found in a number of other disease states, mostly related to mitochondrial dysfunction. Stable-isotope dilution assays were designed for both glutaric acid and 3-hydroxyglutaric acid and their diagnostic sensitivity and specificity were evaluated. Control ranges of glutaric acid in urine were 1.1-9.7 mmol/mol creatinine before and 4.1-32 after hydrolysis. The respective values of 3-hydroxyglutaric acid were 1.4-8.0 and 2.6-11.7 mmol/mol creatnine. For other body fluids, control ranges in mumol/l/L were: for glutaric acid 0.55-2.9 (plasma), 0.18-0.63 (cerebrospinal fluid) and 0.19-0.7 (amniotic fluid); and for 3-hydroxyglutaric acid, 0.2-1.36 (plasma), < 0.2 (cerebrospinal fluid) and 0.22-0.41 (amniotic fluid). Twenty-five patients with GCDH deficiency were studied. Low excretors (12 patients) were defined by a urinary glutaric acid below 100 mmol/mol creatinine down into the normal range, while high excretors (13 patients) had glutaric acid excretions well above this value. With and without hydrolysis there was an overlap of glutaric acid values between patients and controls. Diagnostic sensitivity and specificity of 100% could only be achieved by the quantitative determination of 3-hydroxyglutaric acid with the newly developed stable-isotope dilution assay, allowing an accurate diagnosis of all patients, regardless of the amount of glutaric acid excreted in urine.

Location and distribution of epithelial pearls and tooth buds in human fetuses with cleft lip and palate

OBJECTIVE

The purpose of this study was to establish the location and distribution of epithelial pearls and tooth buds in cleft palate fetuses, relative to the time of palate fusion.

DESIGN

The facial skeletal structures, dental laminae, tooth buds, and epithelial pearls were examined in seven spontaneously aborted human fetuses, of which five had unilateral or bilateral cleft lip and palate or cleft palate. The sectioned fetuses were reconstructed by 3D-computer technology.

RESULTS

Epithelial pearls were found in four of the investigated cases, of which one was a control specimen. They were located at the margins of the palatal shelves. In the cleft lip and palate cases, the cleft was found in the premaxilla between the first and second incisor tooth. The premaxilla was found to be hypoplastic in both bilateral cleft lip and palate cases and was totally absent in the unilateral cleft lip and palate case. The maxilla was hypoplastic in one case with unilateral cleft lip and palate. In all other specimens, it was developed symmetrically.

CONCLUSIONS

The results indicate that cleft lip and palate development may occur after the fusion of the frontonasal prominence with the maxillary prominence and the palatal shelves, as well as a nonfusion of the palatal shelves in the secondary palate.

Partial trisomy 13 in an infant with a mild phenotype: application of fluorescence in situ hybridization in cytogenetic syndromes

We report on a month-old infant with dysmorphic face and several anomalies known to be associated with trisomy 13. Fluorescence in situ hybridization (FISH) studies performed on metaphase cells allowed us to identify an extra material on the short arm of the chromosome 13 as a duplication of 13q22-qter.