Agata Fiumara

Mutations in the DBP-Deficiency Protein HSD17B4 Cause Ovarian Dysgenesis, Hearing Loss, and Ataxia of Perrault Syndrome

Perrault syndrome is a recessive disorder characterized by ovarian dysgenesis in females, sensorineural deafness in both males and females, and in some patients, neurological manifestations. No genes for Perrault syndrome have heretofore been identified. A small family of mixed European ancestry includes two sisters with well-characterized Perrault syndrome. Whole-exome sequencing of genomic DNA from one of these sisters revealed exactly one gene with two rare functional variants: HSD17B4, which encodes 17beta-hydroxysteroid dehydrogenase type 4 (HSD17B4), also known as D-bifunctional protein (DBP). HSD17B4/DBP is a multifunctional peroxisomal enzyme involved in fatty acid beta-oxidation and steroid metabolism. Both sisters are compound heterozygotes for HSD17B4 c.650A>G (p.Y217C) (maternal allele) and HSB17B4 c.1704T>A (p.Y568X) (paternal allele). The missense mutation is predicted by structural analysis to destabilize the HSD17B4 dehydrogenase domain. The nonsense mutation leads to very low levels of HSD17B4 transcript. Expression of mutant HSD17B4 protein in a compound heterozygote was severely reduced. Mutations in HSD17B4 are known to cause DBP deficiency, an autosomal-recessive disorder of peroxisomal fatty acid beta-oxidation that is generally fatal within the first two years of life. No females with DBP deficiency surviving past puberty have been reported, and ovarian dysgenesis has not previously been associated with this illness. Six other families with Perrault syndrome have wild-type sequences of HSD17B4. These results indicate that Perrault syndrome and DBP deficiency overlap clinically; that Perrault syndrome is genetically heterogeneous; that DBP deficiency may be underdiagnosed; and that whole-exome sequencing can reveal critical genes in small, nonconsanguineous families.

DPM2-CDG: A muscular dystrophy-dystroglycanopathy syndrome with severe epilepsy

Congenital disorders of glycosylation (CDG) are a group of metabolic diseases due to defects in protein and lipid glycosylation. We searched for the primary defect in 3 children from 2 families with a severe neurological phenotype, including profound developmental delay, intractable epilepsy, progressive microcephaly, severe hypotonia with elevated blood creatine kinase levels, and early fatal outcome. There was clinical evidence of a muscular dystrophy–dystroglycanopathy syndrome, supported by deficient O‐mannosylation by muscle immunohistochemistry.

Autism and Phenylketonuria

Phenylketonuria (PKU) has been also reported in children with infantile autism (IA); however, the frequency of this association is variably reported. Patients with various forms of hyperphenylalaninemia (HPA) were evaluated applying two methods: the Autism Diagnostic Interview-Revised (ADI-R) and the Childhood Autism Rating Scale (CARS). A total of 243 patients were investigated, 97 with classical PKU, 62 identified by neonatal screening, and 35 late diagnosed. None out of 62 patients with classic PKU diagnosed early met criteria for autism. In the group of 35 patients diagnosed late, two boys (5.71%) ages 16 and 13 years fulfilled the diagnostic criteria for autism. The present study confirms that classical PKU is one of the causes of autism, but the prevalence seems to be very low.

Autism: evidence of association with adenosine deaminase genetic polymorphism

Abstract Reduced adenosine deaminase (ADA) activity has been reported in sera of autistic children relative to controls. Additionally, the Asn allele of the ADA Asp8Asn polymorphism has been associated with reduced enzymatic activity. Therefore, we studied this polymorphism in autistic children and controls from two Italian populations. We observed a significantly elevated frequency of the low-activity Asn allele in the total sample of autistic cases relative to controls (P<0.00001), and in both study populations (P<0.001 and P<0.025). We suggest that this putative genotype-dependent reduction in ADA activity may be a risk factor for the development of autism.

Phosphomannomutase deficiency is the main cause of carbohydrate-deficient glycoprotein syndrome with type I isoelectrofocusing pattern of serum sialotransferrins

J. JAEKEN1*, J. ARTIGAS2, R. BARONE3, A. FIUMARA3, T. J. DE KONING4, B. T. POLL-THE4, J. F. DE RIJK-VAN ANDEL5, G. F. HOFFMANN6, B. ASSMANN6, E. MAYATEPEK7, M. PINEDA8, M. A. VILASECA8, J. M. SAUDUBRAY9, B. SCHLÜTER10, R. WEVERS11 and E. VAN SCHAFTINGEN12 1Department of Pediatrics, University of Leuven, Belgium; 2Department of Pediatrics, Parc Taulí Hospitals, Sabadell, Spain; 3Department of Pediatrics, University of Catania, Italy; 4Wilhelmina Children’s Hospital, Utrecht, The Netherlands; 5Department of Neurology, Ignatius Hospital Breda, The Netherlands; 6University Children’s Hospital, Marburg, Germany; 7Department of Pediatrics, University of Heidelberg, Germany; 8University Hospital Sant Joan de Déu, Barcelona, Spain; 9Department of Pediatrics, Hôpital des Enfants Malades, Paris, France; 10Vestische Kinderklinik, Datteln, Germany; 11Institutes of Neurology, Pediatrics and Radiology, University Hospital Nijmegen, The Netherlands; 12Laboratory of Physiological Chemistry, ICP and University of Louvain, Belgium

Clinical and neuroradiological findings in classic infantile and late‐onset globoid‐cell leukodystrophy (Krabbe disease)

In the present study the clinical course and imaging of early and late-onset forms of Krabbe disease are analyzed. We report on 11 patients with a biochemical diagnosis of galactosyl ceramide beta-galactoside deficiency. Two presented as the classic infantile form and died within the second year of life. In 9 children the first clinical signs, such as gait difficulties and visual failure, started after age 2 years. All these patients developed slow regression of motor and mental capacities, and most of them died within their first decade. In patients of both groups computed tomography (CT) and magnetic resonance imaging (MRI) were performed. In the late-onset form, hypodensities of the central white matter and pyramidal tracts were the leading radiological signs, whereas in the early-onset form, hyperdensities and cerebellar white matter lesions were also detected. From our results it becomes clear that variability of Krabbe disease refers not only to clinical manifestation but also to CT and MRI findings. Better knowledge of phenotypic and radiological diversity will help to understand the pathogenesis of the disease.

Identification and characterization of 15 novel GALC gene mutations causing Krabbe disease.

The characterization of the underlying GALC gene lesions was performed in 30 unrelated patients affected by Krabbe disease, an autosomal recessive leukodystrophy caused by the deficiency of lysosomal enzyme galactocerebrosidase. The GALC mutational spectrum comprised 33 distinct mutant (including 15 previously unreported) alleles. With the exception of 4 novel missense mutations that replaced evolutionarily highly conserved residues (p.P318R, p.G323R, p.I384T, p.Y490N), most of the newly described lesions altered mRNA processing. These included 7 frameshift mutations (c.61delG, c.408delA, c.521delA, c.1171_1175delCATTCinsA, c.1405_1407delCTCinsT, c.302_308dupAAATAGG, c.1819_1826dupGTTACAGG), 3 nonsense mutations (p.R69X, p.K88X, p.R127X) one of which (p.K88X) mediated the skipping of exon 2, and a splicing mutation (c.1489+1G>A) which induced the partial skipping of exon 13. In addition, 6 previously unreported GALC polymorphisms were identified. The functional significance of the novel GALC missense mutations and polymorphisms was investigated using the MutPred analysis tool. This study, reporting one of the largest genotype‐phenotype analyses of the GALC gene so far performed in a European Krabbe disease cohort, revealed that the Italian GALC mutational profile differs significantly from other populations of European origin. This is due in part to a GALC missense substitution (p.G553R) that occurs at high frequency on a common founder haplotype background in patients originating from the Naples region.

Perrault syndrome: Evidence for progressive nervous system involvement

Perrault syndrome (PS) comprises gonadal dysgenesis and sensorineural deafness in females, and deafness in affected males. More recent studies have asked whether the neurological signs in some of the patients are a coincidental finding or part of the syndrome. We report on two pairs of sisters with gonadal dysgenesis and deafness, cerebral, and ocular involvement who developed a progressive, severe sensory, and motor neuropathy. This observation constitutes further evidence of peripheral nervous system involvement in PS. Based on the clinical observations of known patients, two forms of PS may be distinguished: one apparently non‐progressive form and another (exemplified by our two sets of sisters) with apparently progressive axonal‐cerebellar degeneration.

Two new mild homozygous mutations in Gaucher disease patients: Clinical signs and biochemical analyses

Gaucher disease (GD) is a lysosomal storage disorder resulting from impaired activity of lysosomal beta-glucocerebrosidase. More than 60 mutations have been described in the GBA gene. They have been classified as lethal, severe, and mild on the basis of the corresponding phenotype. The fact that most GD patients are compound heterozygous and that most type 1 patients bear the N370S allele, which by itself causes a mild phenotype, make it difficult to correlate the clinical signs with the mutations. Besides N370S, about 10 mild mutations have been described, but only one undoubtedly classified as mild was found at homozygosity. Here we report 2 novel mutations, I402T and V375L, at homozygosity in 2 adult Italian type 1 GD patients. Some properties of the I402T fibroblast enzyme have been compared to those of the enzyme from cells of several N370S/N370S patients. Analysis of the catalytic properties and heat stability as well as the response to phosphatidylserine and sphingolipid activator protein indicate a marked similarity between the 2 enzymes. The finding of another, unrelated patient bearing the I402T mutation (in this case as a compound heterozygote with mutation N370S) suggests that this allele might be quite frequent in the area of Sicily from where both patients originated. In conclusion, the phenotypic expression in the 2 homozygous patients presented here and the biochemical data for one of them allowed the classification of these mutations as mild thus extending the group of mild mutations found at homozygosity.

Congenital disorders of glycosylation with emphasis on cerebellar involvement.

Congenital disorders of glycosylation (CDG) are genetic diseases due to defective glycosylation of proteins and lipids. The authors present an update on these disorders affecting the central nervous system with a focus on cerebellar involvement. The rate of identification of novel CDG shows an exponential increase. Some 76 CDG are actually known, not taking into account the defects in glycan-modifying proteins. Neurologic involvement is present in the large majority of CDG. Screening methods are limited to serum transferrin isoelectrofocusing (for N-glycosylation disorders with sialic acid deficiency), and serum apolipoprotein C-III isoelectrofocusing (for core 1 mucin-type O-glycosylation disorders). Whole exome/genome sequencing is increasingly used in the diagnostic workup of patients with CDG-X. Treatment is greatly lagging behind because only one CDG is efficiently treatable (MPI-CDG). Cerebellar involvement is an important feature of PMM2-CDG, the congenital muscular dystrophies due to dystroglycanopathy, and SRD5A3-CDG. It has also been reported in some patients with ALG1-CDG, ALG3-CDG, ALG9-CDG, ALG6-CDG, ALG8-CDG, PIGA-CDG, DPM1-CDG, DPM2-CDG, B4GALT1-CDG, SLC35A2-CDG, COG1-CDG, COG5-CDG, COG7-CDG, and COG8-CDG.