Prenatal diagnosis of a constitutional interstitial deletion of chromosome 5 (q15q31.1) presenting with features of congenital contractural arachnodactyly

A Novel Splice Site Mutation in the FBN2 Gene in a Chinese Family with Congenital Contractural Arachnodactyly

Congenital contractural arachnodactyly (CCA) is a rare connective tissue disorder characterized by arachnodactyly, multiple joint contractures, progressive kyphoscoliosis, pectus deformity and abnormal crumpled ears. FBN2 is the only gene currently known to be associated with CCA. In this study, we report on a prenatal case presented with skeletal, cardiac and spinal malformations. And his father had elongated limbs, contractures of the proximal interphalangeal joints, high myopia and scoliosis. We conducted whole exome sequencing (WES) on the fetus-parental trio and a heterozygous variant (hg19 chr5:127,673,685, c.3598 + 4A > G, NM_001999.4) in intron 27 of the FBN2 gene was successfully identified, inherited from the father. Reverse transcriptase-polymerase chain reaction (RT-PCR) was performed to evaluate the potential splicing effect of this variant, which confirmed that the variant caused a deletion of exon 27 (126 bp) by disrupting the splice-donor site and destroyed the 17th calcium-binding epidermal growth factor-like (cbEGF) domain. Our research not only finds the etiology of the disease in affected individuals and expands the mutation spectrum of FBN2 gene, but also provides genetic counseling and fertility guidance for this family.

The fibrillinopathies: new insights with focus on the paradigm of opposing phenotypes for both FBN1 and FBN2

Different pathogenic variants in the fibrillin‐1 gene (FBN1) cause Marfan syndrome and acromelic dysplasias. Whereas the musculoskeletal features of Marfan syndrome involve tall stature, arachnodactyly, joint hypermobility, and muscle hypoplasia, acromelic dysplasia patients present with short stature, brachydactyly, stiff joints, and hypermuscularity. Similarly, pathogenic variants in the fibrillin‐2 gene (FBN2) cause either a Marfanoid congenital contractural arachnodactyly or a FBN2‐related acromelic dysplasia that most prominently presents with brachydactyly. The phenotypic and molecular resemblances between both the FBN1 and FBN2‐related disorders suggest that reciprocal pathomechanistic lessons can be learned. In this review, we provide an updated overview and comparison of the phenotypic and mutational spectra of both the “tall” and “short” fibrillinopathies. The future parallel functional study of both FBN1/2‐related disorders will reveal new insights into how pathogenic fibrillin variants differently affect the fibrillin microfibril network and/or growth factor homeostasis in clinically opposite syndromes. This knowledge may eventually be translated into new therapeutic approaches by targeting or modulating the fibrillin microfibril network and/or the signaling pathways under its control.

Family with congenital contractural arachnodactyly due to a novel multiexon deletion of the FBN2 gene

Congenital contractural arachnodactyly (CCA) is caused by pathogenic FBN2 variants; however, the contributions of copy number variations (CNVs) to CCA are still unknown. Here, we report on a familial case of CCA, in which a novel multiexon deletion of exons 35-39 in FBN2 was identified after simple CNV prediction.

Congenital contractural arachnodactyly suspected by abnormally long extremities by fetal ultrasound

Congenital contractural arachnodactyly (CCA) is a rare disease with the clinical features of limited extension of multiple joints, arachnodactyly, camptodactyly, thin and long extremities, and so on. In the point of long extremities, CCA resembles Marfan syndrome (MFS). CCA is easily differentiated from MFS after birth due to the flexion of multiple joints, including elbows, knees, hips and fingers. During the fetal period, observation of arachnodactyly and folded fingers by fetal ultrasound is the means of differential diagnosis between these two diseases. We report on a case of CCA diagnosed with prenatal symptoms of long extremities, and introduced physiotherapy in early childhood for a better physical prognosis.

Severe congenital contractural arachnodactyly caused by biallelic pathogenic variants in FBN2

Fibrillin-2, encoded by FBN2, plays an important role in the early process of elastic fiber assembly. To date, heterozygous pathogenic variants in FBN2 have been shown to cause congenital contractural arachnodactyly (CCA; Beals-Hecht syndrome). Classical CCA is characterized by long and slender fingers and toes, ear deformities, joint contractures at birth, clubfeet, muscular hypoplasia and often tall stature. In individuals with a severe CCA form, different cardiovascular or gastrointestinal anomalies have been described. Here, we report on a 15-year-old girl with a severe form of CCA and novel biallelic variants in FBN2. The girl inherited the missense variant c.3563G > T/p.(Gly1188Val) from her unaffected father and the nonsense variant c.6831C > A/p.(Cys2277*) from her healthy mother. We could detect only a small amount of FBN2 transcripts harboring the nonsense variant in leukocyte-derived mRNA from the patient and mother suggesting nonsense-mediated mRNA decay. As the father did not show any clinical signs of CCA we hypothesize the missense variant c.3563G > T to be a hypomorphic allele. Taken together, our data suggests that severe CCA can be inherited in an autosomal-recessive manner by compound heterozygosity of a hypomorphic and a null allele of the FBN2 gene.

Based on a cohort of 52,879 microarrays, recurrent intragenic FBN2 deletion encompassing exons 1-8 does not cause Beals syndrome

INTRODUCTION

Congenital contractural arachnodactyly (CCA) is a rare connective tissue disorder, associated with heterozygous mutations in the FBN2 gene. The objective of this study was to evaluate the prevalence of an intragenic deletion encompassing exons 1-8 of FBN2 gene in Israeli population.

MATERIALS AND METHODS

A search for intragenic FBN2 microdeletions was performed in two databases of chromosomal microarray analysis (CMA) - genetic laboratory of a tertiary medical center (the primary cohort) and one of the largest Israeli health maintenance organizations (replication cohort).

RESULTS

Overall, 52,879 microarray tests were searched for FBN2 microdeletions. The primary cohort constituted of 18,301 CMA tests, among which 33 intragenic FBN2 microdeletions in unrelated individuals were found (0.18%). Prenatal prevalence of this variant was 0.23% (28/12,604), and specifically in low risk pregnancies - 0.29% (22/7464). Of the 28 cases with known parental origin, 27 (96.4%) were of full or partial Ashkenazi Jewish ethnic background. The approximate allele incidence in the Ashkenazi Jewish origin was 0.4% (18/4961). Combined with the 34,578 CMA tests in the replication cohort, the overall frequency of FBN2 microdeletions was 0.24% (125/52,879). None of the pre- or postnatal cases had any clinical manifestations of CCA.

DISCUSSION

Intragenic FBN2 microdeletions are found in one of every 420 CMA analyses in Israeli population, and in particular one of every 340 low-risk pregnancies. Due to high allele incidence in Ashkenazi Jewish population (1:275), we suggest that FBN2 gene deletion detected by CMA among Ashkenazi Jews should be interpreted as benign copy number variant.

Beals syndrome (congenital contractural arachnodactyly): prenatal ultrasound findings and molecular analysis

We report the prenatal findings in two cases of Beals syndrome. Both pregnancies presented with clinical features of arthrogryposis multiplex congenita/fetal akinesia syndrome (AMC/FAS), including clenched fists and multiple joint contractures on repeat prenatal ultrasound examinations. The first case was diagnosed as having Beals syndrome on physical examination shortly after birth and the diagnosis was confirmed by DNA analysis, shown as a point mutation in the fibrillin 2 (FBN2) gene. The second case was diagnosed with Beals syndrome following microarray analysis on amniocytes, which showed a deletion of the FBN2 gene. Although most cases with AMC/FAS carry a poor prognosis, Beals syndrome is consistent with normal cognitive development and a better prognosis. Thus, making the correct diagnosis is crucial, both pre- and postnatally, for accurate counseling and management.

A syndromic form of Pierre Robin sequence is caused by 5q23 deletions encompassing FBN2 and PHAX

Pierre Robin sequence (PRS) is an aetiologically distinct subgroup of cleft palate. We aimed to define the critical genomic interval from five different 5q22-5q31 deletions associated with PRS or PRS-associated features and assess each gene within the region as a candidate for the PRS component of the phenotype. Clinical array-based comparative genome hybridisation (aCGH) data were used to define a 2.08 Mb minimum region of overlap among four de novo deletions and one mother-son inherited deletion associated with at least one component of PRS. Commonly associated anomalies were talipes equinovarus (TEV), finger contractures and crumpled ear helices. Expression analysis of the orthologous genes within the PRS critical region in embryonic mice showed that the strongest candidate genes were FBN2 and PHAX. Targeted aCGH of the critical region and sequencing of these genes in a cohort of 25 PRS patients revealed no plausible disease-causing mutations. In conclusion, deletion of ∼2 Mb on 5q23 region causes a clinically recognisable subtype of PRS. Haploinsufficiency for FBN2 accounts for the digital and auricular features. A possible critical region for TEV is distinct and telomeric to the PRS region. The molecular basis of PRS in these cases remains undetermined but haploinsufficiency for PHAX is a plausible mechanism.

Multidisciplinary treatment of desmoid tumours in Gardner's syndrome due to a large interstitial deletion of chromosome 5q

BACKGROUND AND AIMS

Classic autosomal-dominant familial adenomatous polyposis (FAP) is clinically defined by the development of hundreds to thousands of colorectal adenomas beginning in childhood and adolescence. A variant of FAP characterized by polyposis in combination with osteomas or soft tissue tumours is called Gardner's syndrome. FAP is caused by germline inactivation of the APC (adenomatous polyposis coli) tumour-suppressor gene located on the long arm of chromosome 5 (5q21-5q22). Cytogenetically visible deletions of chromosome 5q encompassing APC have very rarely been reported. Here, we aimed to phenotypically and genetically characterize a patient with a heterozygous 5q deletion resulting in Gardner's syndrome.

METHODS AND RESULTS

A 26-year-old female patient with mild mental handicap and dysmorphic features due to a cytogenetically visible deletion on chromosome 5q (microscopically estimated region 5q14-5q23) presented at our tertiary referral centre because of mild adenomatous polyposis (<500 polyps). Twenty months after prophylactic proctocolectomy with definitive ileostomy, three rapidly growing desmoids were observed. Tumour-associated complications necessitated a multidisciplinary approach including medical treatment, surgery and radiation therapy. The characterization of the deletion by comparative genomic hybridization identified a large 5q deletion expanding over a 20-Mb region (5q21.3-5q23.3) including the APC gene.

CONCLUSION

Chromosome deletions must be suspected in patients presenting with FAP together with mental handicap and dysmorphic features. This case also impressively shows that FAP-associated desmoids need multimodal treatment taking into account the patient's individual symptoms, disease progression and tumour location.

Deletions and duplications of developmental pathway genes in 5q31 contribute to abnormal phenotypes

Although copy number changes of 5q31 have been rarely reported, deletions have been associated with some common characteristics, such as short stature, failure to thrive, developmental delay (DD)/intellectual disability (ID), club feet, dislocated hips, and dysmorphic features. We report on three individuals with deletions and two individuals with duplications at 5q31, ranging from 3.6 Mb to 8.1 Mb and 830 kb to 3.4 Mb in size, respectively. All five copy number changes are apparently de novo and involve several genes that are important in developmental pathways, including PITX1, SMAD5, and WNT8A. The individuals with deletions have characteristic features including DD, short stature, club feet, cleft or high palate, dysmorphic features, and skeletal anomalies. Haploinsufficiency of PITX1, a transcription factor important for limb development, is likely the cause for the club feet, skeletal anomalies, and cleft/high palate, while additional genes, including SMAD5 and WNT8A, may also contribute to additional phenotypic features. Two patients with deletions also presented with corneal anomalies. To identify a causative gene for the corneal anomalies, we sequenced candidate genes in a family with apparent autosomal dominant keratoconus with suggestive linkage to 5q31, but no mutations in candidate genes were found. The duplications are smaller than the deletions, and the patients with duplications have nonspecific features. Although development is likely affected by increased dosage of the genes in the region, the developmental disruption appears less severe than that seen with deletion.

Genetic influences on joint contractures secondary to immobilization

The primary research question of this study queries whether, beyond environmental conditions, genetic factors affect the development of joint contractures. We hypothesized that intrinsic genetic factors influence the severity of joint contractures developing secondary to joint immobilization. Forty rats from four inbred rat strains had one leg immobilized in knee flexion for 4 weeks. The contracture was measured mechanically as the lack of range of motion to a standardized torque. Using the contralateral leg as a control, the average severity of the contracture could be calculated and compared between strains. All immobilized legs presented knee contractures after 4 weeks of immobilization. Two strains (Dark Agouti and Fisher 344) showed a larger mean knee contracture than those of the two other rat strains (Augustus Copenhagen Irish and Brown Norway). Environmental factors, such as immobility, are usually identified as a cause of a joint contracture. These results demonstrate that, in addition to mechanical factors in the environment of a joint, intrinsic genetic factors participate in the process leading to joint contracture. This demonstration has important consequences for directing future research and may lead to interventions to help patients at risk of developing joint contractures.

Molecular cytogenetic analysis of a de novo interstitial deletion of 5q23.3q31.2 and its phenotypic consequences

We report a 2(3/12)-year-old boy with a constitutional interstitial deletion of 5q,46,XY,del(5)(q23.3q31.2) de novo. Clinical manifestations in this patient included failure to thrive, psychomotor retardation, mild facial dysmorphic features, and long and slender fingers and toes. The precise location and extent (9.5 Mb) of the deletion was determined by fluorescence in situ hybridization (FISH) using 19 YAC and BAC clones. Comparison of the present patient with six other patients with deletions of chromosomal bands 5q22-5q31 allowed further delineation of a constitutional del5q22q31 syndrome. The main features of this syndrome are psychomotor retardation, failure to thrive, hypotonia, hypoplastic muscles, cleft or high arched palate, low-set and dysplastic ears, flat nasal bridge, downslanting palpebral fissures, hypertelorism, anteverted nostrils, and micro- and/or retrognathia.

Molecular characterisation of a prenatally diagnosed 5q15q21.3 deletion and review of the literature

BACKGROUND

Ultrasound examination performed on a 32-year old woman at 30 weeks' gestation showed the presence of fetal malformations. Amniocentesis was performed.

METHODS AND RESULTS

Cytogenetic analysis of cultured amniocytes revealed an interstitial deletion of the long arm of chromosome 5. Molecular studies confirmed that the deletion included the 5q15-21.3 region and was 14 Mb in size. Therefore, the karyotype was: 46,XY,del(5)(q15q21.3). In addition, analysis of polymorphic DNA markers showed that the deletion was of paternal origin.

CONCLUSIONS

The pregnancy was terminated at 34 weeks' gestation. At autopsy, the fetus displayed dysmorphic features, thin limbs and renal abnormalities. The clinical findings observed in the fetus as well as in 20 cases reported previously allowed us to further delineate the phenotype of such interstitial 5q15q21.3 deletions.

Interstitial deletion of the long arm of chromosome 5 in a boy with multiple congenital anomalies and mental retardation: Molecular characterization of the deleted region to 5q22.3q23.3

Interstitial deletions of the middle portion of the long arm of chromosome 5 are relatively rare. So far, only 36 cases have been reported. Because of the repetitive banding pattern of this region, the extent and localization of the deleted segment has not been well characterized in the majority of reported cases. This has complicated attempts to establish a definite karyotype-phenotype correlation. We report a further case with a de novo interstitial deletion of the region 5q?15 to 5q?22 identified by standard karyotype analysis. The proband presented with failure to thrive, developmental delay, distinct craniofacial dysmorphic features, and associated structural anomalies (amongst them cleft palate, iris colobomata, and horseshoe kidney, which have previously been reported in 5q deletion cases). In addition, this child had an Arnold-Chiari type I malformation that required surgical decompression. FISH studies using BAC clones spanning the 5q15 to 5q22 region revealed that these were all present in both homologues. Use of more distal clones allowed delineation of the deleted region to 5q22.3q23.3 and to narrow down the breakpoints to approximately 200 kb. The 14 Mb deleted region contains about 60 genes but, with the possible exception of FBN2 and DMXL1, there are no obvious candidate genes for the specific components of the phenotype. This case illustrates the discrepancy between cytogenetic and molecular techniques in trying to delineate 5q interstitial deletions. Molecular studies need to be performed on these patients, to establish genotype-phenotype correlation and to understand the role and influence of genes in this region.

Familial insertion (3;5)(q25.3;q22.1q31.3) with deletion or duplication of chromosome region 5q22.1-5q31.3 in ten unbalanced carriers

We report on the clinical and cytogenetic data of a large family with an unbalanced insertion translocation (3;5)(q25.3;q22.1q31.3). Analysis of GTG-banded chromosomes demonstrated that unbalanced inheritance of a parental insertion translocation caused either a partial deletion or duplication 5q in this family. The derivative chromosomes were characterized further using microdissection and FISH with band-specific probes. The clinical picture of the proband with a partial deletion of chromosome 5 was characterized by moderate psychomotor retardation, mild facial dysmorphism, cleft palate, and single transverse crease. The family members with a partial duplication of chromosome 5 were borderline intelligent, had mild facial dysmorphism, a cardiac anomaly, and a high-pitched voice. The unbalanced carriers were compared with patients reported in the literature with a duplication or deletion of chromosome region 5q22.1 --> 5q31.3.

Prenatal ultrasound findings in a fetus with congenital contractural arachnodactyly

Congenital contractural arachnodactyly (CCA) or Beals-Hecht syndrome is an autosomal dominant disorder caused by mutations in the fibrillin-2 (FBN2) gene. The principal features of CCA are a marfanoid habitus, multiple congenital contractures, camptodactyly, arachnodactyly, kyphoscoliosis, muscular hypoplasia, and external ear malformations. Our case is the first that shows typical sonographic signs in a fetus at 25 weeks' gestation with molecular genetically verified CCA in a large family with many members affected over four generations. This demonstrates that CCA can be detected prenatally by non-invasive ultrasonography. The importance of confirmation of CCA by means of DNA sequence analysis of the FBN2 gene is stressed.

Ionizing radiation and genetic risks. X. The potential "disease phenotypes" of radiation-induced genetic damage in humans: perspectives from human molecular biology and radiation genetics

Estimates of genetic risks of radiation exposure of humans are traditionally expressed as expected increases in the frequencies of genetic diseases (single-gene, chromosomal and multifactorial) over and above those of naturally-occurring ones in the population. An important assumption in expressing risks in this manner is that gonadal radiation exposures can cause an increase in the frequency of mutations and that this would result in an increase in the frequency of genetic diseases under study. However, despite compelling evidence for radiation-induced mutations in experimental systems, no increases in the frequencies of genetic diseases of concern or other adverse effects (i.e., those which are not formally classified as genetic diseases), have been found in human studies involving parents who have sustained radiation exposures. The known differences between spontaneous mutations that underlie naturally-occurring single-gene diseases and radiation-induced mutations studied in experimental systems now permit us to address and resolve these issues to some extent. The fact that spontaneous mutations (among which are point mutations and DNA deletions generally restricted to the gene) originate through a number of different mechanisms and that the latter are intimately related to the DNA organization of the genes, are now well-documented. Further, spontaneous mutations include those that cause diseases through loss of function as well as gain of function of genes. In contrast, most radiation-induced mutations studied in experimental systems (although identified through the phenotypes of the marker genes) are predominantly multigene deletions which cause loss of function; the recoverability of an induced deletion in a livebirth seems dependent on whether the gene and the genomic region in which it is located can tolerate heterozygosity for the deletion and yet be compatible with viability. In retrospect, the successful mutation test systems (such as the mouse specific locus test) used in radiation studies have involved genes which are non-essential for survival and are also located in genomic regions, likewise non-essential for survival. In contrast, most of the human genes at which induced mutations have been looked for, do not seem to have these attributes. The inference therefore is that the failure to find induced germline mutations in humans is not due to the resistance of human genes to induced mutations but due to the structural and functional constraints associated with their recoverability in livebirths. Since the risk of inducible genetic diseases in humans is estimated using rates of "recovered" mutations in mice, there is a need to introduce appropriate correction factors to bridge the gap between these rates and the rates at which mutations causing diseases are potentially recoverable in humans. Since the whole genome is the "target" for radiation-induced genetic damage, the failure to find increases in the frequencies of specific single-gene diseases of societal concern does not imply that there are no genetic risks of radiation exposures: the problem lies in delineating the phenotypes of recoverable genetic damage that are recognizable in livebirths. Data from studies of naturally-occurring microdeletion syndromes in humans and those from mouse radiation studies are instructive in this regard. They (i) support the view that growth retardation, mental retardation and multisystem developmental abnormalities are likely to be among the quantitatively more important adverse effects of radiation-induced genetic damage than mutations in a few selected genes and (ii) underscore the need to expand the focus in risk estimation from known genetic diseases (as has been the case thus far) to include these induced adverse developmental effects although most of these are not formally classified as "genetic diseases". (ABSTRACT TRUNCATED)