Calidad en genética bioquímica prenatal / Quality in prenatal biochemical genetics

Para diagnosticar enfermedades metabólicas hereditarias(EMH), tanto postnatales como prenatalmente, se empleanlos recursos de la genética bioquímica, que se basanmayoritariamente en el estudio en fluidos biológicos y tejidos de productos génicos (proteínas) y de metabolitos específicos que sean demostrativos o estén directamente relacionados con la pérdida de función de un gen. Las EMH, debido a sus bajas prevalencias individuales, entran en la categoría de enfermedades raras o minoritarias, pero se han descrito centenares de ellas y en general son enfermedades abrumadoras y a menudo letales. Debido a ello y a las dificultadesde tratamiento, su diagnóstico prenatal es muy relevante.En el presente artículo se resumen unos conocimientosmínimos indispensables sobre su complejidad y losmedios del laboratorio para llegar al diagnóstico, a fin de demostrar la importancia que tiene en el diagnóstico prenatal la labor de reunir la máxima información posible acerca del caso índice y de los padres (heterocigotos). Seguidamente se trata el tema de la calidad de los laboratorios y de laspruebas o ensayos de genética bioquímica, incluyendo elcontrol europeo específico de la ERNDIM, el proyecto Eurogentest de la CE para la armonización, validación y estandarización de pruebas genéticas, la Ley 14/2007 de 3 de julio de 2007 de investigación biomédica que define y regula el marco para la realización de pruebas genéticas en investigación y en asistencia y las Normas ISO para la certificación y acreditación de los laboratorios. El artículo finaliza con unrecordatorio de las técnicas y materiales fetales utilizados para el diagnóstico prenatal de las EMH

For the diagnosis of Inherited disorders of metabolism(IDM), postnatal as well as prenatal, we need the resources of Biochemical genetics, which are mainly based in the studies in biological fluids and tissues of the gene products (proteins) and specific metabolites, directly related or demonstratives of a gene function impairment. Because of the very low individual prevalence of IDM, they are consideredrare diseases, but it had been described hundreds ofthem, being moreover overwhelming and often lethal diseases. These facts, together with difficulties for treatment made prenatal diagnosis very relevant. In this paper, there are summarised some essential knowledge on the complexity of IDM and the resources of the laboratory for its diagnosis, in order to show how it is important for the prenatal diagnosis, to collect all the possible information about the index case and the parents (heterozygous). Next, issues are the quality of the biochemical genetics tests and laboratories,including the specific ERNDIM QAP; the FP6 projectEurogentest for the harmonization, validation andstandardization of diagnostic genetic testing; the Spanish bill 14/2007 on biomedical research, that among other issues provides for genetic testing for research as well as for medical care purposes and some concepts on ISO norms for the certification/accreditation of laboratories. Finally, there is a reminder of the technology and foetal materials suitable for the prenatal diagnosis of IDM

X-linked adrenoleukodystrophy in Spain. Identification of 26 novel mutations in the ABCD1 gene in 80 patients. Improvement of genetic counseling in 162 relative females.

In this study, we analyzed the ABCD1 gene in 80 X-linked adrenoleukodystrophy (X-ALD) patients from 62 unrelated families. We identified 53 different mutations, of which 26 are novel and two are non-pathogenic sequence variants (L516L and 3'UTR, 2246C/G) that have been previously described. The Spanish population had significant allelic heterogeneity, in which most of the mutations were exclusive to a single family 47/53 (88.7%). Only six mutations (Y174S, G277R, FsE471, R518Q, P543L, and R554H) were found in more than one family. Mutations G277R, P543L, and R554H were the most frequent, each of them being found in three patients (5%). Intra-familiar phenotype variability was observed in most of the families, but in one, with the novel mutation R120P, only the adult mild phenotype was present (five hemizygous family members). We detected 80 heterozygous women by mutation analysis, but only 78 of them showed increased very-long-chain fatty acid levels. In conclusion, this study extends the spectrum of mutations in X-ALD and facilitates the identification of heterozygous females. Our results are also consistent with previous studies reporting the difficulty of predicting genotype-phenotype correlation.

Pilot study for the neonatal screening of fragile X syndrome.

Fragile X syndrome (SFX) is the commonest form of inherited mental retardation. Due to the highly variable phenotype clinical diagnosis is complicated. In nearly all cases, the disorder is caused by expansion of a CGG-repeat in the 5'-untranslated region of the FMR1 (fragile X mental retardation-1) gene. We have evaluated the feasibility, efficiency and costs of two methodologies in order to develop a simple test to screen large populations: PCR and fragile X mental retardation-1 protein (FMRP) immunodetection. We studied 100 newborn males using PCR and immunodetection (26.91 Euro). All but one amplified the CGG repeat of the FMR1 gene within the normal size range. The sample that failed to amplify showed only 28% of FMRP expression by immunodetection study; both results indicated an affected male. A further 100 males were studied only by polymerase chain reaction (PCR) (7.8 Euro); all of them amplified within the normal size range. Both methodologies, PCR and immunodetection, are feasible for screening large populations, PCR being the most suitable, economical and less time-consuming. However, it is advisable to keep slides for immunodetection when PCR fails or the external control shows no amplification. Early detection of SFX-affected individuals would represent a great benefit for their maximum social integration, due to appropriate treatment and early stimulation and would permit a cascade screening in their pedigree.

Control de calidad en el laboratorio de diagnóstico prenatal / Quality control in the prenatal diagnosis laboratory

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Diagnosis and follow-up of a case of peroxisomal disorder with peroxisomal mosaicism.

Peroxisomal disorder phenotypes are the result of mutations that cause defective peroxisomal assembly or alterations in the import mechanism of peroxisomal proteins that lead to multiple peroxisomal dysfunctions, or the result of a peroxisomal enzymatic deficiency with a single peroxisomal dysfunction. With complementation analysis, 16 groups have been found. Assignment of the genetic defect has been described for some of the complementation groups. We describe the clinical evolution and follow-up over 10 years of a patient who belongs to complementation group 4, although he showed a milder clinical course. It has been found in fibroblasts different peroxisome populations, normal processing and expression of beta-oxidation PTS1 and PTS2 proteins, abnormal ALD protein distribution and normal plasmalogen biosynthesis; abnormal beta-oxidation metabolites have also been detected in serum. Ultrastructural studies in liver showed peroxisomal mosaicism as in fibroblasts. It has been taken into account that peroxisomal mosaicism may lead to variability in peroxisomal diagnostic parameters, making difficult the final diagnosis in these patients.

Neuronopathic juvenile glucosylceramidosis due to sap-C deficiency: clinical course, neuropathology and brain lipid composition in this Gaucher disease variant.

Glucosylceramide lipidosis results from a defective lysosomal degradation of this glycolipid. Lipid degradation is controlled by two components, the enzyme beta-glucocerebrosidase and a sphingolipid activator protein. While most Gaucher cases are due to mutations within the gene that codes for the lysosomal enzyme, only two patients have been described with normal enzyme levels and mutations in the gene for the sphingolipid activator protein C (sap-C). Here we present the detailed neurological manifestations, neuropathological findings and brain lipid composition in one sap-C-deficient patient. The patient was an 8-year-old boy who presented with transient losses of consciousness, myoclonic jerks and generalized seizures resistant to all antiepileptic drugs. He developed progressive horizontal ophthalmoplegia, pyramidal and cerebellar signs, and died at the age of 15.5 years. Neuropathological studies demonstrated neuronal cell loss and neuronophagia, massive intraneuronal lipid storage and lack of perivascular Gaucher cells. Electron microscopy examination showed different types of storage including lipofuscin granules as well as the cytosomes with parallel arrays of bilayers that are assumed to be formed by stored lipids. General brain lipid composition did not show a remarkable increase or loss of any of the major lipid fractions but the glucosylceramide concentration in the cortex of several anatomical regions showed a striking increase. Fatty acid composition of the ceramide moiety clearly suggests that gangliosides are the main precursors in the cerebral cortex, while it implies an additional and distinct source in the cerebellum. Studying the phenotypic consequences of mutant sphingolipid activator proteins is critical to a better understanding of the physiological significance of these proteins.

[The diagnosis of peroxisomal disorders in Spain during the period 1987-1997]. / Diagnóstico de las enfermedades peroxisomales en España en el período 1987-1997.

INTRODUCTION: Peroxisomal disorders are divided into two groups: a) Those with alterations in multiple peroxisomal functions, and b) With alterations in only one peroxisomal function. DEVELOPMENT: During the period 1987-1997, using very long chain fatty acids, plasmalogens and phytanic acid as diagnostic parameters, we diagnosed 116 cases of peroxisomal disorders in Spain. The most frequent (76%) was found to be X-linked adrenoleukodystrophy (X-ALD). Of the five phenotypes described in this condition, the adult cerebral form is seen in a higher percentage in the Spanish population (14%) than in other populations studied (1-3%). Defects in the assembly of peroxisomes made up 18%; the commonest phenotype was that of Zellweger's syndrome (13 cases), followed by neonatal adrenoleukodystrophy (5 cases) and infantile Refsum (2 cases). In the latter two patients, study of the hepatic peroxisomes showed a mosaic distribution. Rhizomelic punctate chondroplasia made up 3%, isolated beta-oxidation defects 2% and defects of plasmalogen synthesis 1%. In X-ALD, diagnosis of an initial case led to the detection of 12 presymptomatic and 70 heterozygote persons. Prenatal diagnoses were made on 10 occasions and 7 fetuses found to be affected. The introduction of the study of ALDP expression in the fibroblasts and the profile of the organic acids in the urine has led to improved diagnosis of these disorders.

X-linked adrenoleukodystrophy: phenotype distribution and expression of ALDP in Spanish kindreds.

X-linked adrenoleukodystrophy (X-ALD) is a neurodegenerative disorder caused by an impairment in peroxisomal beta-oxidation of very long straight-chain fatty acids (VLCFAs). Six clinical phenotypes have been delineated: childhood cerebral (CCALD), adolescent cerebral (AdolCALD), adult cerebral (ACALD), adrenomyeloneuropathy (AMN), Addison-only (AO), and presymptomatic (PALD). The distribution of phenotypes varies in different countries. We have diagnosed biochemically 60 X-ALD Spanish patients belonging to 48 kindreds. Their phenotypic distribution was: CCALD plus AdolCALD, 33%; ACALD, 16%; AMN, 27%; AO, 12%; and PALD, 12%. These results contrast with the distribution described in other countries, due to a higher prevalence of the ACALD form. Regarding the expression of the protein product (ALDP), we studied 17 kindreds using immunochemical techniques and found absence of ALDP in 84% of cases. We also studied 13 females from 7 negative ALDP kindreds in order to correlate ALDP expression and the carrier status established by VLCFA measurement. In one case with normal VLCFA levels in serum and fibroblasts, we observed mosaicism in ALDP expression. This fact supports the use of this technique for identifying carriers.

ALDP expression in fetal cells and its application in prenatal diagnosis of X-linked adrenoleukodystrophy.

X-linked adrenoleukodystrophy (X-ALD) is due to an impairment in the peroxisomal beta-oxidation of very long straight chain fatty acids (VLCFAs) and the gene involved encodes a 75 kD protein (ALDP). Prenatal diagnosis is usually made by measurement of VLCFAs in cultured amniotic fluid cells (CAF) and chorionic villus cells (CCV), but some misdiagnoses have been reported. For this reason, some authors suggest the use of more than one strategy to minimize the risk of pitfalls. In this study we show, by immunochemical techniques, that ALDP is expressed in chorionic villi and amniotic cells and can be used for prenatal diagnosis of X-ALD in kindreds where ALDP is absent (69-84 per cent), together with VLCFA determination. Moreover, we demonstrate that the culture medium modifies ALDP expression; therefore, it is a factor that must be taken into account when a prenatal diagnosis is done.

De novo missense mutation Y174S in exon 1 of the adrenoleukodystrophy (ALD) gene.

Adrenoleukodystrophy (ALD) is an X-linked disease, characterised by an alteration of the peroxisomal beta-oxidation of the very long chain fatty acids. The ALD gene has been identified and mutations have been detected in ALD patients. We report here a new missense mutation in the ALD gene of a male patient, predicting a tyrosine to serine substitution at codon 174 (mutation Y174S). The mother of the ALD patient does not have the Y174S mutation in her leukocyte DNA, indicating that Y174S arose de novo in the patient. Y174S is the first reported de novo mutation in the ALD gene.

Diagnosis of X-adrenoleucodystrophy phenotypic variants.

We report the radiological and biochemical data of a familial X-adrenoleucodystrophy with an extreme phenotypic variability, in which the diagnosis of several affected members was delayed for several years. The propositus developed a progressive dementia, while two of his brothers were diagnosed of primary Addison's disease several years previously. MRI in two cases with different phenotypes revealed hyperintense diffuse white matter lesions, and the diagnosis was confirmed by increased serum levels of very long chain fatty acids. We conclude that X-adrenoleucodystrophy should be included in the differential diagnosis of adult Addison's disease even though no neurological involvement or family history is recorded, and that MRI is a useful tool for diagnosis and follow-up of neurological involvement in this disease.

Activator protein deficient Gaucher's disease. A second patient with the newly identified lipid storage disorder.

A report is presented based on the biochemical and immunochemical studies of various tissues from a 15-year-old boy with a neuronopathic form of Gaucher's disease. Qualitative and quantitative lipid analyses revealed a storage of glucosylceramide. The striking feature was that, employing the usual assay methods, a normal activity of the lysosomal enzyme glucosylceramidase was revealed, despite massive lipid accumulation. Immunochemical assays of hepatic and splenic tissue extracts from this atypical Gaucher's patient disclosed the absence of A1 activator protein, which is necessary for the enzyme degradation of glucosylceramide in vivo. This is the second documented case of a patient presenting with glucosylceramide activator protein deficiency.

[Type C Niemann-Pick disease in 2 siblings. Biochemical bases of its diagnosis]. / Enfermedad de Niemann-Pick tipo C en dos hermanos. Bases bioquímicas del diagnóstico.

Two brothers, a seven-year-old male and a nine-year-old female are reported. Clinical features include scholar troubles and clumsiness, hepatosplenomegaly, vertical supranuclear ophthalmoplegia and ataxic gait. Moreover, the girl showed intention tremor. Foamy histiocytes were seen in bone marrow and some Niemann-Pick type Kupffer cells were present in liver. Girl's conjunctival biopsy showed lamellar inclusions. Biochemical studies were performed in girl's skin and liver biopsies. Sphingomyelinase activity assayed with 14C sphingomieline in cultured skin fibroblasts was 26% at the mean control value. Liver lipid composition did not show an appreciable increase of sphingomyelin or cholesterol, but bis (monoacylglyceryl) phosphate was clearly elevated. These data are compatible with Niemann-Pick disease type C.

[Sandhoff disease]. / Enfermedad de Sandhoff.

A new case of Sandhoff disease is presented (gangliosidosis GM2 type II or variant O) with enzymatic study in serum and leukocytes from the patient, as well as in serum from the newborn's, father and mother. The clinical expression, enzymatic study and evolution are discussed comparing them with Tay-Sachs disease (gangliosidosis GM2 type I o variant B).

[Sandhoff's disease (GM2 gangliosidosis, type II). Presentation of a case with a clinical and biochemical study. Carrier detection]. / Enfermedad de Sandhoff (gangliosidosis GM2 tipo II). Presentación de un caso con estudio clínico y bioquímico. Investigación de portadores.

A case affected by Sandhoff's disease is reported, with clinical and biochemical studies. In the propositus, total absence of hexosaminidases is reported. In parents hexosaminidase A is present, but hexosaminidase B is decreased. In the carriers there is a total low activity of hexosaminidase and a lower proportion 20% of hexosaminidase is confirmed.