Maria Grazia Pomponi

Characterization of MSH2 and MLH1 mutations in Italian families with hereditary nonpolyposis colorectal cancer

Mismatch repair genes MSH2 and MLH1 are considered to be the two major genes that are responsible for hereditary nonpolyposis colorectal cancer (HNPCC). Germline heterozygous inactivating mutations of MSH2 and MLH1 have been identified previously in a substantial fraction of individuals who are predisposed genetically to colorectal carcinoma (CRC) and other tumors of the HNPCC spectrum. With the aim of determining the relevance of these two genes in the Italian population, we submitted to mutational analysis a set of 17 HNPCC families, all of which fulfilled the “Amsterdam criteria.” A combination of different techniques, including reverse transcription‐polymerase chain reaction (RT‐PCR) of long fragments and single‐strand conformation polymorphism (SSCP) on cDNA and genomic DNA, allowed the identification of ten molecular variants, seven of which are predicted to inactivate mismatch repair function. The mutated predisposing gene was MSH2 in two families and MLH1 in five other families. All of the mutations were characterized by DNA sequencing and appeared to involve different molecular mechanisms, such as short in‐frame and out‐of‐frame deletions, splicing errors, and nonsense mutations. This study also demonstrates that, in the Italian population, a considerable fraction of HNPCC families (at least 41%) is linked to MSH2 and MLH1 mutations. Genes Chromosom. Cancer 18:8–18, 1997.

Expansion to full mutation of a FMR1 intermediate allele over two generations

Fragile X syndrome is due to an expanded CGG repeat in the 5′ UTR of the FMR1 gene. According to repeat size, we distinguish four allele categories: normal (<40 CGG), intermediate (46–60 CGG), premutated (55–200 CGG) and full mutated (>200 CGG). However, the boundaries among these categories are unclear, making it difficult to classify unstable alleles and to estimate the risk of expansion. We report a family with a proband, carrying a methylated full mutation with an amplification of 1.2 kb. PCR analysis demonstrated two alleles of 29 and 61 CGGs in the mother. Sequencing of the 61 CGG allele showed no AGG interruptions. Both mothers sisters had two alleles of 31 and 44 CGGs, and the daughter of one of these had two alleles of 22 and 44 repeats, demonstrating stable transmission of the 44 CGG allele. The maternal grandfather was deceased, but haplotype reconstruction using markers DXS548 and FRAXAC1 demonstrated that he was carrier of the premutated allele. Furthermore, molecular analysis confirmed the same paternity with a probability of 99.79% for all the three sisters. According to these findings, it is likely that the maternal grandfather carried the 44 CGG allele, showing unstable transmission, given that it expanded first to 61 CGGs in one daughter, and then to full mutation in her child. Although we cannot exclude paternal mosaicism, it is likely that a rare event of progression from an intermediate to a premutated and on to a full mutated allele occurred in this family over two generations.

A unique case of reversion to normal size of a maternal premutation FMR1 allele in a normal boy.

Fragile X syndrome (FXS) is caused mostly by expansion and subsequent methylation of the CGG repeat in the 5′UTR of the FMR1 gene, resulting in silencing of the gene, absence of FMRP and development of the FXS phenotype. The expansion also predisposes the CGG repeat and the flanking regions to further instability that may lead to mosaics between a full mutation and a premutation or, rarely, a normal or deleted allele. Here, we report on a 10-year-old boy with no FXS phenotype, who has a normal CGG tract, although he inherited the maternal expanded allele that causes FXS in his two brothers. Southern blotting demonstrated that the mother carries a premutation allele (∼190 CGG), whereas the propositus shows a normal 5.2 kb fragment after HindIII digestion and a smaller 2.2 kb fragment after double HindIII-EagI digestion, without any apparent mosaicism in peripheral blood leukocytes. PCR and sequence analysis of the FMR1 5′UTR revealed an allele of 43 repeats, with two interspersed AGG triplets in position 10 and 25 and an exceptional CCG triplet in position 17. This latter creates an abnormal EagI site compatible with the smaller 2.2 kb fragment observed with Southern blotting. Haplotype analysis proved that the rearranged allele originated from the maternal expanded allele. To the best of our knowledge, this is the first non-mosaic case of reduction in the CGG tract of the FMR1 gene, resulting in a normal allele.

A new single-nucleotide deletion of PMP22 in an HNPP family without recurrent palsies

In this study we describe four patients from the same kindred who were affected by an autosomal‐dominantly inherited peripheral neuropathy. They presented an unusual combination of clinical, electrophysiological, and pathological findings in association with a new mutation of the PMP22 gene. Clinically, three patients had carpal tunnel syndrome symptoms and one patient had late‐onset peroneal atrophy. Motor and sensory nerve conduction velocities were reduced without focal slowing at entrapment sites. Nerve biopsy disclosed diffuse hypomyelination with focal thickening of the myelin sheath in some fibers. Sequence analysis of the PMP22 gene showed a single‐nucleotide deletion (227delG) in the affected patients. This mutation, which has not been reported previously, leads to an open reading frame shift and probably to a truncated and unstable PMP22 protein. We conclude that this novel 227delG mutation of PMP22 gives a mild form of hereditary neuropathy with liability to pressure palsy with atypical clinical and electrophysiological findings. Muscle Nerve, 2008

Simpson–Golabi–Behmel syndrome type 1 in a 27-week macrosomic preterm newborn: The diagnostic value of rib malformations and index nail and finger hypoplasia†

The Simpson–Golabi–Behmel syndrome type 1 (SGBS1, OMIM #312870) is an X‐linked overgrowth condition comprising abnormal facial appearance, supernumerary nipples, congenital heart defects, polydactyly, fingernail hypoplasia, increased risk of neonatal death and of neoplasia. It is caused by mutation/deletion of the GPC3 gene. We describe a macrosomic 27‐week preterm newborn with SGBS1 who presents a novel GPC3 mutation and emphasize the phenotypic aspects which allow a correct diagnosis neonatally in particular the rib malformations, hypoplasia of index finger and of the same fingernail, and 2nd–3rd finger syndactyly.

The Simpson-Golabi-Behmel syndrome: a clinical case and a detective story

The Simpson–Golabi–Behmel syndrome (SGBS) is an overgrowth condition comprising “coarseness” of facial traits, supernumerary nipples, congenital heart defects, polydactyly and fingernail hypoplasia, and an increased risk of neonatal death and later neoplasia. Psychomotor development is usually normal. The syndrome is caused by mutation/deletion of the X‐linked gene GPC3. We describe a new case of SGBS, that led to the discovery of an extended family segregating a GPC3 mutation and, ultimately, of an affected relative forgotten, but not lost, in an anatomical museum, where he was classified as a macrosomic newborn, who was born probably around 1940 and died neonatally of unknown cause. This baby boy becomes the oldest case of SGBS on record.

A premature infant with Costello syndrome due to a rare G13C HRAS mutation

Costello syndrome is caused by mutations in the HRAS proto‐oncogene whose clinical features in the first year of life include fetal and neonatal macrosomia with subsequent growth impairment due to severe feeding difficulties. We report on a premature male with Costello syndrome due to a rare G13C HRAS mutation and describe his clinical features and evolution during the first year of life. The diagnosis of Costello syndrome may be difficult at birth, especially in very preterm infants in whom feeding difficulties, reduced subcutaneous adipose tissue and failure to thrive are also part of their typical presentation.

Correlation between GJB2 mutations and audiological deficits : personal experience

Mutations in GJB2 gene are the most common cause of genetic deafness. More than 100 mutations have been described. The aim of this work is to describe the personal experience in genetic hearing loss, investigating the audiological and genetical characteristics of Cx26 deafness and correlating genotype and phenotype. We performed audiological and genetical evaluation in 154 patients affected by non-syndromic deafness of different degree. All patients showed a bilateral symmetrical sensorineural hearing loss. From the genetical analysis 127 probands resulted as negatives while 27 as positives (51.8% homozygous for 35 delG, 14.8% compound heterozygosis and 33.3% single mutation); 7.5% of patients had a mild deafness, 37% moderate, 33.3% severe and 22.2% profound. The c.35 delG mutation was detected in 66.6% of patients. Three mutations were found in compound heterozygosis with 35 delG, six different single mutations already described, and a new mutation S138G were also found. Correlation between genotype and phenotype confirmed the high variability of hearing loss.

Skewed X-inactivation in carriers establishes linkage in an X-linked deafness-mental retardation syndrome.

Frank J. Probst, Peter Hedera, Anthony M. Sclafani, Maria Grazia Pomponi, Giovanni Neri, Jessica Tyson, Julie A. Douglas, Elizabeth M. Petty, and Donna M. Martin Department of Pediatrics, Cornell University Medical Center, New York, New York Department of Neurology, Vanderbilt University, Nashville, Tennessee Department of Pediatrics, The University of Michigan, Ann Arbor, Michigan Department of Human Genetics, The University of Michigan, Ann Arbor, Michigan Department of Internal Medicine, The University of Michigan, Ann Arbor, Michigan Istituto di Genetica Medica, Universita Cattolica, Rome, Italy Clinical and Molecular Genetics Unit, Institute of Child Health, London, England

Simpson–Golabi–Behmel syndrome in a female: A case report and an unsolved issue

Simpson–Golabi–Behmel syndrome is an X‐linked recessive overgrowth condition caused by alterations in GPC3 gene, encoding for the cell surface receptor glypican 3, whose clinical manifestations in affected males are well known. Conversely, there is little information regarding affected females, with very few reported cases, and a clinical definition of this phenotype is still lacking. In the present report we describe an additional case, the first to receive a primary molecular diagnosis based on strong clinical suspicion. Possible explanations for full clinical expression of X‐linked recessive conditions in females include several mechanisms, such as skewed X inactivation or homozygosity/compound heterozygosity of the causal mutation. Both of these were excluded in our case. Given that the possibility of full expression of SGBS in females is now firmly established, we recommend that GPC3 analysis be performed in all suggestive female cases.