Valeria Chiavetta

Lack of association of HOXA1 and HOXB1 mutations and autism in Sicilian (Italian) patients

Lack of association of HOXA1 and HOXB1 mutations and autism in Sicilian (Italian) patients

Exon deletions of the phenylalanine hydroxylase gene in Italian hyperphenylalaninemics

A consistent finding of many studies describing the spectrum of mutant phenylalanine hydroxylase (PAH) alleles underlying hyperphenylalaninemia is the impossibility of achieving a 100% mutation ascertainment rate using conventional gene-scanning methods. These methods include denaturing gradient gel electrophoresis (DGGE), denaturing high performance liquid chromatography (DHPLC), and direct sequencing. In recent years, it has been shown that a significant proportion of undetermined alleles consist of large deletions overlapping one or more exons. These deletions have been difficult to detect in compound heterozygotes using gene-scanning methods due to a masking effect of the non-deleted allele. To date, no systematic search has been carried out for such exon deletions in Italian patients with phenylketonuria or mild hyperphenylalaninemia. We used multiplex ligation- dependent probe amplification (MLPA), comparative multiplex dosage analysis (CMDA), and real-time PCR to search for both large deletions and duplications of the phenylalanine hydroxylase gene in Italian hyperphenylalaninemia patients. Four deletions removing different phenylalanine hydroxylase (PAH) gene exons were identified in 12 patients. Two of these deletions involving exons 4-5-6-7-8 (systematic name c.353-?_912 + ?del) and exon 6 (systematic name c.510-?_706 + ?del) have not been reported previously. In this study, we show that exon deletion of the PAH gene accounts for 1.7% of all mutant PAH alleles in Italian hyperphenylalaninemics.

Analysis of the gastrin-releasing peptide receptor gene in Italian patients with autism spectrum disorders†

The gastrin‐releasing peptide receptor (GRPR) was implicated for the first time in the pathogenesis of Autism spectrum disorders (ASD) by Ishikawa‐Brush et al. [Ishikawa‐Brush et al. (1997): Hum Mol Genet 6: 1241–1250]. Since this original observation, only one association study [Marui et al. (2004): Brain Dev 26: 5–7] has further investigated, though unsuccessfully, the involvement of the GRPR gene in ASD. With the aim of contributing further information to this topic we have sequenced the entire coding region and the intron/exon junctions of the GRPR gene in 149 Italian autistic patients. The results of this study led to the identification of four novel point mutations, two of which, that is, C6S and L181F, involve amino acid changes identified in two patients with ASD and Rett syndrome, respectively. Both the leucine at position 181 and the cysteine at position 6 are strongly conserved in vertebrates. C6S and L181F mutant proteins were expressed in COS‐7 and BALB/3T3 cells, but they did not affect either GRPs binding affinity or its potency for stimulating phospholipase C‐mediated production of inositol 1,4,5‐trisphosphate. In summary, our results do not provide support for a major role of the GRPR gene in ASD in the population of patients we have studied. However, there is a potential role of C6S and L181F mutations on GRPR function, and possibly in the pathogenesis of the autistic disorders in the two patients.

Preliminary studies on the molecular basis of hyperphenylalaninemia in Egypt

Abstract Mutation analysis at the phenylalanine hydroxylase (PAH) locus was undertaken in 56 Egyptian hyperphenylalaninemic patients. Selected screening for 11 known mutations and denaturing Gradient gel electrophoresis (DGGE) analysis of the entire coding sequence and exon/intron boundaries led to the identification of a new mutation (I224T), four previously described mutations, and several polymorphisms. Overall, 18 mutant alleles could thus be characterized. In contrast to the high mutation detection rate typical of the DGGE-based scanning approach, only 6 of 16 mutant alleles tested were identified. Since BH4 deficiency could not be excluded in any of these patients, the latter results may be explained by the occurrence of mutations affecting the genes controlling the synthesis and recycling of tetrahydrobiopterin: the cofactor of PAH. An alternative hypothesis is also discussed.

Multiplex ligation-dependent probe amplification detection of an unknown large deletion of the CREB-binding protein gene in a patient with Rubinstein-Taybi syndrome

Rubinstein-Taybi syndrome is a rare autosomal dominant congenital disorder characterized by postnatal growth retardation, psychomotor developmental delay, skeletal anomalies, peculiar facial morphology, and tumorigenesis. Mutations in the gene encoding the cAMP response element-binding protein (CREB, also known as CREBBP or CBP) on chromosome 16p13.3 have been identified. In addition, some patients with low intelligence quotients and autistic features bear large deletions. Based on these observations, we used multiplex ligation-dependent probe amplification to search for large deletions affecting the CREBBP gene in a Rubinstein-Taybi syndrome patient. We identified a novel heterozygote deletion removing five exons (exons 17-21), encoding the histone acetyltransferase domain. We propose the use of multiplex ligation-dependent probe amplification as a fast, accurate and cheap test for detecting large deletions in the CREBBP gene in the sub-group of Rubinstein-Taybi syndrome patients with low intelligence quotients and autistic features.

Carrier screening for spinal muscular atrophy in Italian population

Spinal muscular atrophy (SMA) is an autosomal-recessive neuromuscular disorder characterized by motor neuron degeneration in the anterior horn of the spinal cord and brain stem, resulting in progressive muscle weakness and atrophy. The responsible survival motor neuron gene (SMN1; HGNC: 11117) is localized in 5q11.2-13.3. Screening for carriers of SMA is necessary for effective clinical/prenatal diagnosis and genetic counselling. In this study, the copy number of SMN1 gene was determined from a southern Italian population to estimate carrier frequency. This is the first report addressing the estimation of SMA carrier frequency in an Italian population. Our results show that the SMA carrier frequency in Sicily is higher than in the European populations and lower than in Mediterranean/Middle Eastern countries. The carrier testing could be a helpful tool for genetic counselling, to individuals with a positive family history. SMA is the second most common severe autosomalrecessive disorder after cystic fibrosis and the most frequent genetic cause of infant mortality, with an incidence of one per 6000–10,000 live births (Pearn 1980). Mutations in the survival motor neuron gene (SMN1; HGNC: 11117), localized in 5q11.2-13.3 within a large inverted duplicated element, cause SMA types I, II, III and IV (Lefebvre et al. 1995). Further, between 95% and 98% of individuals with recessive SMA have two deletion mutations (deletion of exons 7–8) and the remaining 2–5% have one deletion mutation (exons 7–8) and a second, different type of mutation (Ogino and Wilson 2002). People generally have between one and three copies of the SMN1 gene. Usually, people with two copies

Novel deletion of the E3A ubiquitin protein ligase gene detected by multiplex ligation-dependent probe amplification in a patient with Angelman syndrome

Angelman syndrome (AS) is a severe neurobehavioural disorder caused by failure of expression of the maternal copy of the imprinted domain located on 15q11-q13. There are different mechanisms leading to AS: maternal microdeletion, uniparental disomy, defects in a putative imprinting centre, mutations of the E3 ubiquitin protein ligase (UBE3A) gene. However, some of suspected cases of AS are still scored negative to all the latter mutations. Recently, it has been shown that a proportion of negative cases bear large deletions overlapping one or more exons of the UBE3A gene. These deletions are difficult to detect by conventional gene-scanning methods due to the masking effect by the non-deleted allele. In this study, we have used for the first time multiplex ligation-dependent probe amplification (MLPA) and comparative multiplex dosage analysis (CMDA) to search for large deletions affecting the UBE3A gene. Using this approach, we identified a novel causative deletion involving exon 8 in an affected sibling. Based on our results, we propose the use of MLPA as a fast, accurate and inexpensive test to detect large deletions in the UBE3A gene in a small but significant percentage of AS patients.

An interesting case of Piebaldism with cafè-au-lait macules and freckling: the use of targeted next-generation sequencing for molecular diagnosis

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Comparative multiplex dosage analysis in spinocerebellar ataxia type 2 patients.

We developed a new application of comparative multiplex dosage analysis (CMDA) for evaluation of the ataxin 2 gene. Expansions of the triplet CAG can cause spinocerebellar ataxia type 2 (SCA2), a neurodegenerative disease with an autosomal-dominant mode of inheritance. Molecular diagnosis of SCA2 is routinely based on the use of conventional PCR to detect the CAG expansion. However, PCR does not amplify an allele with an expansion of many triplets (>80), which is typically found in infantile and juvenile forms of SCA2, thus leading to false negatives. We propose the analysis of the ATXN2 gene by CMDA to complement existing methods currently used for the detection of large expansions of the CAG repeat. Using CMDA, the presence of any longer mutated allele in a heterozygous patient or fetus would be inferred due to dosage variation of the very frequent normal allele #22. CMDA can be completed in 1 day, at very low cost, and would be a useful tool for prenatal diagnosis and for diagnosis of presymptomatic forms of early-onset SCA2.