Maria Teresa Divizia

Rubinstein-Taybi Syndrome: spectrum of CREBBP mutations in Italian patients

BackgroundRubinstein-Taybi Syndrome (RSTS, MIM 180849) is a rare congenital disorder characterized by mental and growth retardation, broad and duplicated distal phalanges of thumbs and halluces, facial dysmorphisms and increased risk of tumors. RSTS is caused by chromosomal rearrangements and point mutations in one copy of the CREB-binding protein gene (CREBBP or CBP) in 16p13.3. To date mutations in CREBBP have been reported in 56.6% of RSTS patients and an average figure of 10% has ascribed to deletions.MethodsOur study is based on the mutation analysis of CREBBP in 31 Italian RSTS patients using segregation analysis of intragenic microsatellites, BAC FISH and direct sequencing of PCR and RT-PCR fragments.ResultsWe identified a total of five deletions, two of the entire gene and three, all in a mosaic condition, involving either the 5 or the 3 region. By direct sequencing a total of 14 de novo mutations were identified: 10 truncating (5 frameshift and 5 nonsense), one splice site, and three novel missense mutations. Two of the latter affect the HAT domain, while one maps within the conserved nuclear receptor binding of (aa 1–170) and will probably destroy a Nuclear Localization Signal. Identification of the p.Asn1978Ser in the healthy mother of a patient also carrying a de novo frameshift mutation, questions the pathogenetic significance of the missense change reported as recurrent mutation. Thirteen additional polymorphisms, three as of yet unreported, were also detected.ConclusionA high detection rate (61.3%) of mutations is confirmed by this Italian study which also attests one of the highest microdeletion rate (16%) documented so far.

Microarray based analysis of an inherited terminal 3p26.3 deletion, containing only the CHL1 gene, from a normal father to his two affected children

Backgroundterminal deletions of the distal portion of the short arm of chromosome 3 cause a rare contiguous gene disorder characterized by growth retardation, developmental delay, mental retardation, dysmorphisms, microcephaly and ptosis. The phenotype of individuals with deletions varies from normal to severe. It was suggested that a 1,5 Mb minimal terminal deletion including the two genes CRBN and CNTN4 is sufficient to cause the syndrome.In addition the CHL1 gene, mapping at 3p26.3 distally to CRBN and CNTN4, was proposed as candidate gene for a non specific mental retardation because of its high level of expression in the brain.Methods and Resultswe describe two affected siblings in which array-CGH analysis disclosed an identical discontinuous terminal 3p26.3 deletion spanning less than 1 Mb. The deletion was transmitted from their normal father and included only the CHL1 gene. The two brothers present microcephaly, light mental retardation, learning and language difficulties but not the typical phenotype manifestations described in 3p- syndrome.Conclusiona terminal 3p26.3 deletion including only the CHL1 gene is a very rare finding previously reported only in one family. The phenotype of the affected individuals in the two families is very similar and the deletion has been inherited from an apparently normal parent. As already described for others recurrent syndromes with variable phenotype, these findings are challenging in genetic counselling because of an evident variable penetrance.

The first intron of the human osteopontin gene contains a C/EBP-beta-responsive enhancer.

The osteopontin (OPN) protein is found expressed at high level in several processes including fibrotic evolution of organ injuries, tumorigenesis, and immune response. The molecular mechanisms that underly overexpression, especially at the transcriptional level, have been only partially clarified. Therefore, this study was undertaken in search for additional DNA elements in the regulatory regions of the OPN gene and cognate transcription factors. Our results on the region upstream of the transcription start site confirmed that essential elements are located within the first 100 bp. Analysis of the sequence that includes the first untranslated exon and first intron revealed that it could enhance the promoter activity. Experiments of transfection of constructs containing different fragments of this sequence showed that most of the enhancer activity was confined in the terminal 30-bp tract of the first intron, although it was not functioning in a myofibroblast cell line. DNA/protein binding assays and cotransfection experiments showed that the C/EBP-beta transcription factor was able to bind a recognition sequence in this 30-bp segment. We found a bi-allelic sequence polymorphism at +245 in the first intron, which did not show a significant functional effect, but is a useful tool for future association studies.

De novo deletion of chromosome 11q12.3 in monozygotic twins affected by Poland Syndrome

BackgroundPoland Syndrome (PS) is a rare disorder characterized by hypoplasia/aplasia of the pectoralis major muscle, variably associated with thoracic and upper limb anomalies. Familial recurrence has been reported indicating that PS could have a genetic basis, though the genetic mechanisms underlying PS development are still unknown.Case presentationHere we describe a couple of monozygotic (MZ) twin girls, both presenting with Poland Syndrome. They carry a de novo heterozygous 126 Kbp deletion at chromosome 11q12.3 involving 5 genes, four of which, namely HRASLS5, RARRES3, HRASLS2, and PLA2G16, encode proteins that regulate cellular growth, differentiation, and apoptosis, mainly through Ras-mediated signaling pathways.ConclusionsPhenotype concordance between the monozygotic twin probands provides evidence supporting the genetic control of PS. As genes controlling cell growth and differentiation may be related to morphological defects originating during development, we postulate that the observed chromosome deletion could be causative of the phenotype observed in the twin girls and the deleted genes could play a role in PS development.

A spectrum of LMX1B mutations in Nail-Patella syndrome: New point mutations, deletion, and evidence of mosaicism in unaffected parents

Purpose: Nail-Patella syndrome (MIM 161200) is a rare autosomal dominant disorder characterized by hypoplastic or absent patellae, dystrophic nails, dysplasia of the elbows, and iliac horn. In 40% of cases, a glomerular defect is present and, less frequently, ocular damage is observed. Inter- and intrafamilial variable expressivity of the clinical phenotype is a common finding. Mutations in the human LMX1B gene have been demonstrated to be responsible for Nail-Patella syndrome in around 80% of cases.Methods: Standard polymerase chain reaction and sequencing methods were used for mutation and single nucleotide polymorphism identification and control of cloned sequences. Array-CGH (Agilent, 244A Kit) was used for detection of deletions. Standard cloning techniques and the Snapshot method were used for analysis of mosaicism.Results: In this study, we present the results of LMX1B screening of 20 Nail-Patella syndrome patients. The molecular defect was found in 17 patients. We report five novel mutations and a ∼2 Mb deletion in chromosome 9q encompassing the entire LMX1B gene in a patient with a complex phenotype. We present evidence of somatic mosaicism in unaffected parents in two cases, which, to our knowledge, are the first reported cases of inheritance of a mutated LMX1B allele in Nail-Patella syndrome patients from a mosaic parent.Conclusion: The study of the described case series provides some original observations in an “old” genetic disorder.

Hand and upper limb anomalies in poland syndrome: A new proposal of classification

Background: The Poland anomaly (PA) comprises unilateral absence or hypoplasia of the pectoralis major muscle and a variable degree of ipsilateral hand and upper limb anomalies. Various hand and upper limb anomalies classifications in PA have been previously published. In this work, a new classification of hand and upper limb anomalies in PA is proposed, on the basis of the clinical and instrumental evaluation of 175 patients. Methods: The patients have been followed by a multidisciplinary approach, consisting in orthopaedic, surgical, and genetic evaluation and chest, upper limb, and ultrasound examination of major and minor pectoralis muscles, heart, and kidney. Results: Hand and upper limb anomalies were classified in 8 groups on the basis of the clinical degree of severity and on the basis of the presence of coexisting associated anomalies. Data regarding the sex and laterality, previously reported in the medical literature, were confirmed by our analysis. Etiopathogenetic mechanisms leading to the anomaly are discussed. Conclusions: The proposed classification is derived from the observation of the widest group of patients described in the medical literature. Our proposal could help in the management of patients affected by Poland syndrome and in understanding etiological and pathologic aspects of the disease. Level of Evidence: IV.

Familial Poland anomaly revisited

Poland anomaly (PA) is a pectoral muscle hypoplasia/aplasia variably associated with ipsilateral thoracic (TA) and/or upper limb anomalies (ULA). PA is usually sporadic and sometimes familial, making recurrence risk an issue in genetic counseling. Multidisciplinary evaluation of 240 PA patients was carried out, including physical examination of patients and their parents in 190 PA (subjects of the study). Familial conditions were classified into three groups. Group1: true familial PA (F‐PA): pectoral muscle defects with familial recurrence: 8(4.2%). Group2: familial Poland‐like anomaly families (F‐PLA): PA index case and ≥1 relative(s) showing normal pectoral muscles but ULA and/or TA common in PA: 16(8.4%). Group3: sporadic PA (S‐PA): 166(87.4%). F‐PA indicated a stronger male (87.5%) and left side (62.5%) prevalence, but fewer ULA (37.5%) compared to the other two groups. Maternal transmission (6/8) was more common in F‐PA. Statistical significance was not reached due to the small number of F‐PA and F‐PLA. Karyotyping and array‐comparative genomic hybridization were performed in 13 families. Three maternally inherited copy number variants were identified in three patients: 1p31.1 deletion, Xp11.22 duplication, and 16q23.1 duplication. Interestingly, the probands mother carrying the 16q23.1 duplication displayed moderate breast and areola asymmetry, but normal pectoral muscles on ultrasound. Though there is no recent review discussing recurrence of PA, we reviewed 31 published PA families. On the basis of our study and previous reports, familial PA is not uncommon. Nonetheless, no information can be derived either regarding a molecular basis or clinical tools with which to identify cases with recurrence risk.

Genotype-Phenotype Correlation of 2q37 Deletions Including NPPC Gene Associated with Skeletal Malformations

Coordinated bone growth is controlled by numerous mechanisms which are only partially understood because of the involvement of many hormones and local regulators. The C-type Natriuretic Peptide (CNP), encoded by NPPC gene located on chromosome 2q37.1, is a molecule that regulates endochondral ossification of the cartilaginous growth plate and influences longitudinal bone growth. Two independent studies have described three patients with a Marfan-like phenotype presenting a de novo balanced translocation involving the same chromosomal region 2q37.1 and overexpression of NPPC. We report on two partially overlapping interstitial 2q37 deletions identified by array CGH. The two patients showed opposite phenotypes characterized by short stature and skeletal overgrowth, respectively. The patient with short stature presented a 2q37 deletion causing the loss of one copy of the NPPC gene and the truncation of the DIS3L2 gene with normal CNP plasma concentration. The deletion identified in the patient with a Marfan-like phenotype interrupted the DIS3L2 gene without involving the NPPC gene. In addition, a strongly elevated CNP plasma concentration was found in this patient. A possible role of NPPC as causative of the two opposite phenotypes is discussed in this study.

EEC- and ADULT-associated TP63 mutations exhibit functional heterogeneity toward P63 responsive sequences.

TP63 germ‐line mutations are responsible for a group of human ectodermal dysplasia syndromes, underlining the key role of P63 in the development of ectoderm‐derived tissues. Here, we report the identification of two TP63 alleles, G134V (p.Gly173Val) and insR155 (p.Thr193_Tyr194insArg), associated to ADULT and EEC syndromes, respectively. These alleles, along with previously identified G134D (p.Gly173Asp) and R204W (p.Arg243Trp), were functionally characterized in yeast, studied in a mammalian cell line and modeled based on the crystal structure of the P63 DNA‐binding domain. Although the p.Arg243Trp mutant showed both complete loss of transactivation function and ability to interfere over wild‐type P63, the impact of p.Gly173Asp, p.Gly173Val, and p.Thr193_Tyr194insArg varied depending on the response element (RE) tested. Interestingly, p.Gly173Asp and p.Gly173Val mutants were characterized by a severe defect in transactivation along with interfering ability on two DN‐P63α‐specific REs derived from genes closely related to the clinical manifestations of the TP63‐associated syndromes, namely PERP and COL18A1. The modeling of the mutations supported the distinct functional effect of each mutant. The present results highlight the importance of integrating different functional endpoints that take in account the features of P63 proteins target sequences to examine the impact of TP63 mutations and the associated clinical variability.

Novel mutations in the L1CAM gene support the complexity of L1 syndrome.

X-linked hydrocephalus, MASA syndrome, X-linked complicated Spastic Paraplegia Type I and X-linked partial agenesis of the corpus callosum are the four rare diseases usually referred to L1 syndrome, caused by mutations in the L1CAM gene. By direct sequencing of L1CAM in 16 patients, we were able to identify seven mutations, five of which were never described before. Patients phenotype evaluation revealed a correlation between the number of clinical features typical of L1 syndrome and the chance to find causative mutation. Our findings support that L1CAM mutations are associated with widely heterogeneous phenotypes, however the occurrence of several clinical features remains the best criterion for planning molecular testing both in familial and apparently sporadic cases.