Terminal deletion of the long arm of chromosome 3 [46,XX,del(3)(q27-->qter)]

Isoform-Specific Roles of Mutant p63 in Human Diseases

Simple Summary

The protein p63 belongs to the family of the p53 tumor suppressor. Mouse models have, however, shown that it is not a classical tumor suppressor but instead involved in developmental processes. Mutations in the p63 gene cause several developmental defects in human patients characterized by limb deformation, cleft lip/palate, and ectodermal dysplasia due to p63’s role as a master regulator of epidermal development. In addition, p63 plays a key role as a quality control factor in oocytes and p63 mutations can result either in compromised genetic quality control or premature cell death of all oocytes.

Abstract

The p63 gene encodes a master regulator of epidermal commitment, development, and differentiation. Heterozygous mutations in the DNA binding domain cause Ectrodactyly, Ectodermal Dysplasia, characterized by limb deformation, cleft lip/palate, and ectodermal dysplasia while mutations in in the C-terminal domain of the α-isoform cause Ankyloblepharon-Ectodermal defects-Cleft lip/palate (AEC) syndrome, a life-threatening disorder characterized by skin fragility, severe, long-lasting skin erosions, and cleft lip/palate. The molecular disease mechanisms of these syndromes have recently become elucidated and have enhanced our understanding of the role of p63 in epidermal development. Here we review the molecular cause and functional consequences of these p63-mutations for skin development and discuss the consequences of p63 mutations for female fertility.

Deletions and loss-of-function variants in TP63 associated with orofacial clefting

We aimed to identify novel deletions and variants of TP63 associated with orofacial clefting (OFC). Copy number variants were assessed in three OFC families using microarray analysis. Subsequently, we analyzed TP63 in a cohort of 1072 individuals affected with OFC and 706 population-based controls using molecular inversion probes (MIPs). We identified partial deletions of TP63 in individuals from three families affected with OFC. In the OFC cohort, we identified several TP63 variants predicting to cause loss-of-function alleles, including a frameshift variant c.569_576del (p.(Ala190Aspfs*5)) and a nonsense variant c.997C>T (p.(Gln333*)) that introduces a premature stop codon in the DNA-binding domain. In addition, we identified the first missense variants in the oligomerization domain c.1213G>A (p.(Val405Met)), which occurred in individuals with OFC. This variant was shown to abrogate oligomerization of mutant p63 protein into oligomeric complexes, and therefore likely represents a loss-of-function allele rather than a dominant-negative. All of these variants were inherited from an unaffected parent, suggesting reduced penetrance of such loss-of-function alleles. Our data indicate that loss-of-function alleles in TP63 can also give rise to OFC as the main phenotype. We have uncovered the dosage-dependent functions of p63, which were previously rejected.

Master regulatory role of p63 in epidermal development and disease

The transcription factor p63 is a master regulator of epidermal development. Mutations in p63 give rise to human developmental diseases that often manifest epidermal defects. In this review, we summarize major p63 isoforms identified so far and p63 mutation-associated human diseases that show epidermal defects. We discuss key roles of p63 in epidermal keratinocyte proliferation and differentiation, emphasizing its master regulatory control of the gene expression pattern and epigenetic landscape that define epidermal fate. We subsequently review the essential function of p63 during epidermal commitment and transdifferentiation towards epithelial lineages, highlighting the notion that p63 is the guardian of the epithelial lineage. Finally, we discuss current therapeutic development strategies for p63 mutation-associated diseases. Our review proposes future directions for dissecting p63-controlled mechanisms in normal and diseased epidermal development and for developing therapeutic options.

Oculocerebral hypopigmentation syndrome maps to chromosome 3q27.1q29

BACKGROUND

In 1967, Cross et al. [J Pediatr 1967;70:398-406] reported four siblings with intellectual disability, microcephaly, neurologic and ocular disorders, and hypopigmentation involving skin and hair. This novel entity, known as oculocerebral hypopigmentation syndrome (OCHS) or Cross syndrome (OMIM 257800), is assumed to be autosomal recessive. However, its genetic cause is still unknown.

CASE REPORT

A 4-year-old girl is reported with OCHS, a history of recurrent infections and vertebral fusion of L4-L5. Central nervous system and cardiac imaging as well as metabolic screening were normal. Microscopic hair investigations did not show any melanin deposit defects.

RESULTS

Using molecular cytogenetics, we detected a de novo interstitial del(3)(q27.1q29) of the paternal chromosome. To our knowledge, this is the first molecular genetics finding in a patient with OCHS. Here we discuss the genotype-phenotype correlations and suggest candidate genes for this disorder.

CONCLUSION

Investigating further patients would enable fine-mapping the OCHS locus and identifying its putative gene.

Mutant p63 causes defective expansion of ectodermal progenitor cells and impaired FGF signalling in AEC syndrome

Ankyloblepharon-ectodermal defects-cleft lip/palate (AEC) syndrome, which is characterized by cleft palate and severe defects of the skin, is an autosomal dominant disorder caused by mutations in the gene encoding transcription factor p63. Here, we report the generation of a knock-in mouse model for AEC syndrome (p63(+/L514F) ) that recapitulates the human disorder. The AEC mutation exerts a selective dominant-negative function on wild-type p63 by affecting progenitor cell expansion during ectodermal development leading to a defective epidermal stem cell compartment. These phenotypes are associated with impairment of fibroblast growth factor (FGF) signalling resulting from reduced expression of Fgfr2 and Fgfr3, direct p63 target genes. In parallel, a defective stem cell compartment is observed in humans affected by AEC syndrome and in Fgfr2b(-/-) mice. Restoring Fgfr2b expression in p63(+/L514F) epithelial cells by treatment with FGF7 reactivates downstream mitogen-activated protein kinase signalling and cell proliferation. These findings establish a functional link between FGF signalling and p63 in the expansion of epithelial progenitor cells and provide mechanistic insights into the pathogenesis of AEC syndrome.

Regulation of skin aging and heart development by TAp63

Since the discovery of the TP63 gene in 1998, many studies have demonstrated that ΔNp63, a p63 isoform of the p53 gene family, is involved in multiple functions during skin development and in adult stem/progenitor cell regulation. In contrast, TAp63 studies have been mostly restricted to its apoptotic function and more recently as the guardian of oocyte integrity. TAp63 endogenous expression is barely detectable in embryos and adult (except in oocytes), presumably because of its rapid degradation and the lack of antibodies able to detect weak expression. Nevertheless, two recent independent studies have demonstrated novel functions for TAp63 that could have potential implications to human pathologies. The first discovery is related to the protective role of TAp63 on premature aging. TAp63 controls skin homeostasis by maintaining dermal and epidermal progenitor/stem cell pool and protecting them from senescence, DNA damage and genomic instability. The second study is related to the role of TAp63, expressed by the primitive endoderm, on heart development. This unexpected role for TAp63 has been discovered by manipulation of embryonic stem cells in vitro and confirmed by the severe cardiomyopathy observed in brdm2 p63-null embryonic hearts. Interestingly, in both cases, TAp63 acts in a cell-nonautonomous manner on adjacent cells. Here, we discuss these findings and their potential connection during development.

The 3q29 microdeletion syndrome: report of three new unrelated patients and in silico "RNA binding" analysis of the 3q29 region

The human 3q29 microdeletion syndrome is associated with mild facial dysmorphism, developmental delay and variable congenital malformations. We report three new unrelated patients with this syndrome. We also performed in silico RNA binding analysis in silico on the 3q29 critical region genes. Several genes within this genomic region including DLG1 and RNF168 are predicted to bind RNA. While recessive mutations in RNF168 cause RIDDLE syndrome, an immune deficiency and radiosensitivity disorder, the potential impact of heterozygous deletion of RNF168 on patients with the 3q29 deletion syndrome is still unknown.

p63, a story of mice and men

The transcription factor p63 is essential for the formation of the epidermis and other stratifying epithelia. This is clearly demonstrated by the severe abnormality of p63-deficient mice and by the development of certain types of ectodermal dysplasias in humans as a result of p63 mutations. Investigation of the in vivo functions of p63 is complicated by the occurrence of 10 different splicing isoforms and by its interaction with the other family members, p53 and p73. In vitro and in vivo models have been used to unravel the functions of p63 and its different isoforms, but the results or their interpretation are often contradictory. This review focuses on what mammalian in vivo models and patient studies have taught us in the last 10 years.

Multiple Congenital Malformations Including Severe Eye Anomalies and Abnormal Cerebellar Development with Dandy-Walker Malformation in a Girl with Partial Trisomy 3q

PURPOSE

Ocular anomalies have been associated with numerous chromosomal abnormalities. This report describes partial trisomy 3q in a two-month-old girl with dysmorphic features of the Dup3q phenotype and severe eye and cerebellar malformations.

METHODS

Clinical examination and chromosomal analysis were conducted.

RESULTS

The karyotype of the propositus was 46,XX, ins(3)(pter --> p25::q27 --> q21::p25 --> qter). She had an abnormal head shape, low-set malformed ears, coarse facies, short webbed neck, abnormal foot position, polycystic kidney, and spina bifida. There was also bilateral microphthalmia that was more severe on the right side, microcornea, and corneal opacity. She had posterior fossa abnormalities, including cerebellar vermis hypoplasia suggestive of a Dandy-Walker (DW) malformation.

CONCLUSIONS

This girl with an intrachromosomal duplication of distal 3q and typical phenotype belongs to the severe end of the spectrum for such cases. The ocular manifestations of the 3q duplication syndrome provide additional evidence of the involvement of developmental eye genes in this chromosomal segment.

A case of 3q29 microdeletion with novel features and a review of cytogenetically visible terminal 3q deletions

A further case of 3q29 deletion, in a 13-year-old boy, is described and compared with previous reports. Our case shares a number of dysmorphic and neurodevelopmental features with previously reported individuals with 3q29 microdeletion and is the second reported case with deceleration in head growth--which may be a useful diagnostic clue. Novel features, which may expand the phenotype, include nasal voice, six lumbar vertebrae, lower limb contractures and cerebral sigmoid venous thrombosis. Additionally, cases with cytogenetically visible terminal 3q deletions are reviewed.

Screening for subtelomeric rearrangements in 210 patients with unexplained mental retardation using multiplex ligation dependent probe amplification (MLPA)

BACKGROUND

Subtelomeric rearrangements contribute to idiopathic mental retardation and human malformations, sometimes as distinct mental retardation syndromes. However, for most subtelomeric defects a characteristic clinical phenotype remains to be elucidated.

OBJECTIVE

To screen for submicroscopic subtelomeric aberrations using multiplex ligation dependent probe amplification (MLPA).

METHODS

210 individuals with unexplained mental retardation were studied. A new set of subtelomeric probes, the SALSA P036 human telomere test kit, was used.

RESULTS

A subtelomeric aberration was identified in 14 patients (6.7%) (10 deletions and four duplications). Five deletions were de novo; four were inherited from phenotypically normal parents, suggesting that these were polymorphisms. For one deletion, DNA samples of the parents were not available. Two de novo submicroscopic duplications were detected (dup 5qter, dup 12pter), while the other duplications (dup 18qter and dup 22qter) were inherited from phenotypically similarly affected parents. All clinically relevant aberrations (de novo or inherited from similarly affected parents) occurred in patients with a clinical score of >or=3 using an established checklist for subtelomeric rearrangements. Testing of patients with a clinical score of >or=3 increased the diagnostic yield twofold to 12.4%. Abnormalities with clinical relevance occurred in 6.3%, 5.1%, and 1.7% of mildly, moderately, and severely retarded patients, respectively, indicating that testing for subtelomeric aberrations among mildly retarded individuals is necessary.

CONCLUSIONS

The value of MLPA is confirmed. Subtelomeric screening can be offered to all mentally retarded patients, although clinical preselection increases the percentage of chromosomal aberrations detected. Duplications may be a more common cause of mental retardation than has been appreciated.

Prenatal diagnosis of primary anophthalmia with a 3q27 interstitial deletion involving SOX2

We report an interstitial deletion of chromosome 3q26-q28 in a fetus in which anophthalmia had been detected prenatally. FISH analysis, using BAC clones encompassing the SOX2 locus, showed that SOX2 gene was involved in the chromosomal breakpoint of the deletion. This case confirms that haploinsufficiency for SOX2 plays a crucial role in human eye development and emphasizes the necessity of careful chromosomal analysis, including FISH analysis of the 3q region, in case of prenatal discovery of anophthalmia.

Ophthalmic genetics/inherited eye disease

PURPOSE OF REVIEW

Genetic diseases of the eye and involving the eye continue as a leading cause of blindness in children and adults.

RECENT FINDINGS

Most genetic ocular disorders are not yet treatable and/or are without curative therapies because of our limited understanding of pathogenesis, and the need for well-designed and fully implemented animal model or human clinical trial testing of therapeutic methods.

SUMMARY

Herein are current reviews of a variety of ophthalmologic genetic disorders such as anophthalmia, aniridia, albinism, anterior segment dysgenesis, Marfan syndrome, ectopia lentis, neurofibromatosis, retinal hemangioblastomas, and familial exudative vitreoretinopathy.

Dilated cardiomyopathy in a 3-year-old girl with a terminal deletion, 46,XX,del(3)(q27-qter), of the long arm of chromosome 3

We report a case in which a 3-year-old girl with terminal deletion of the long arm of chromosome 3 had dilated cardiomyopathy, a complication that has not previously been reported in association with this chromosome abnormality. In addition to cardiomyopathy, she had intrauterine growth retardation, small eyes and mouth, a broad nose, thin lips, low-set ears, a short neck and overlapping second toes.

CONCLUSION

due to the paucity of reported cases of 3q deletion, and the clinical variability of such cases, identification of a distinct 3q phenotype (including cardiac complications) remains elusive.

Telomeres: a diagnosis at the end of the chromosomes

In recent years, subtelomeric rearrangements have been identified as a major cause of mental retardation and/or malformation syndromes. So far, over 2500 subjects with mental retardation have been tested and reported of whom approximately 5% appeared to have a subtelomeric rearrangement. In this review, the clinical aspects of each known (submicroscopic) subtelomeric deletion will be presented and the various methods available for detecting subtelomeric abnormalities will be discussed. Not only will the patients and their families benefit from a good collection and report of the various telomeric abnormalities and their clinical phenotype, but it will also give more insight into the aetiology of mental retardation and malformation syndromes.

Mutations in SOX2 cause anophthalmia

A submicroscopic deletion containing SOX2 was identified at the 3q breakpoint in a child with t(3;11)(q26.3;p11.2) associated with bilateral anophthalmia. Subsequent SOX2 mutation analysis identified de novo truncating mutations of SOX2 in 4 of 35 (11%) individuals with anophthalmia. Both eyes were affected in all cases with an identified mutation.

Delineation of an estimated 6.7 MB candidate interval for an anophthalmia gene at 3q26.33-q28 and description of the syndrome associated with visible chromosome deletions of this region

Anophthalmia or microphthalmia occur in approximately one in 10 children who have severe visual impairment. These eye malformations are often of unknown aetiology, but can be inherited in autosomal dominant, recessive or X-linked forms, and can also occur in association with specific chromosome abnormalities. Four children are described in the medical literature with microphthalmia or anophthalmia in association with chromosome rearrangements involving distal 3q, suggesting the presence of a micro/anophthalmia gene in this region. We have identified two further patients with micro/anophthalmia and chromosome rearrangements involving 3q26-->3q27 and identified a 6.7 MB common deleted region. Patient 1 had multiple abnormalities including bilateral anophthalmia, abnormalities of the first and second cranial nerves and partial absence of the corpus callosum. His karyotype was 46,XY,del(3)(q26.33q28). Patient 2 had right anophthalmia and left extreme microphthalmia. Her karyotype was 46,XX,del(3)(q26.33q28)t(3;7)(q28;q21.1). Both patients had intrauterine growth retardation (IUGR) and strikingly similar dysmorphic facies consisting of bossed forehead, downward-slanting palpebral fissures, grooved bridge of the nose, prominent low-set ears, small down-turned mouth and small mandible. We identified BAC clones mapping to distal 3q from the ENSEMBL and NCBI Entrez databases. These BAC clones were used as fluorescence in situ hybridisation (FISH) probes to identify the minimum deleted region common to both patients. This interval, between clones RPC11-134F2 and RPC11-132N15, was estimated to be 6.7 MB. We conclude that there is an anophthalmia locus within this interval. Candidate genes mapping to this region include Chordin and DVL3, a homologue of the Drosophila Dishevelled gene.

P63 gene mutations and human developmental syndromes

The P63 gene is a recently discovered member of the p53 family. While P53 is ubiquitously expressed, p63 is expressed specifically in embryonic ectoderm and in the basal regenerative layers of epithelial tissues in the adult. Complete abrogation of P63 gene function in an animal model points to the relevance of P63 for the proper development of ectodermally derived tissues. The p63 knockout mouse dies at birth and has truncation of the limbs, as well as absence of epidermis, prostate, breast, and urothelial tissues, apparently reflecting ectodermal stem cell loss. A number of dominant human syndromes have been mapped to chromosome 3q27 and ultimately to mutations in the p63 gene. These syndromes have abnormal limb development and/or ectodermal dysplasia and include ectrodactyly, ectodermal dysplasia, clefting syndrome; ankyloblepharon, ectodermal dysplasia, clefting syndrome; acro-dermato-ungual-lacrimal-tooth syndrome; limb-mammary syndrome; as well as nonsyndromic split hand/foot malformation. The pattern of heterozygous mutations is distinct for each of these syndromes. Consistent with this syndrome-specific mutational pattern, the functional consequences of mutations on the p63 proteins also vary, invoking dominant-negative and gain-of-function mechanisms rather than a simple loss of function.

Splitting p63

Causative TP63 mutations have been identified in five distinct human developmental disorders that are characterized by various degrees of limb abnormalities, ectodermal dysplasia, and facial clefts. The distribution of mutations over the various p63 protein domains and the structural and functional implications of these mutations establish a clear genotype-phenotype correlation.

p63 Gene mutations in eec syndrome, limb-mammary syndrome, and isolated split hand-split foot malformation suggest a genotype-phenotype correlation

p63 mutations have been associated with EEC syndrome (ectrodactyly, ectodermal dysplasia, and cleft lip/palate), as well as with nonsyndromic split hand-split foot malformation (SHFM). We performed p63 mutation analysis in a sample of 43 individuals and families affected with EEC syndrome, in 35 individuals affected with SHFM, and in three families with the EEC-like condition limb-mammary syndrome (LMS), which is characterized by ectrodactyly, cleft palate, and mammary-gland abnormalities. The results differed for these three conditions. p63 gene mutations were detected in almost all (40/43) individuals affected with EEC syndrome. Apart from a frameshift mutation in exon 13, all other EEC mutations were missense, predominantly involving codons 204, 227, 279, 280, and 304. In contrast, p63 mutations were detected in only a small proportion (4/35) of patients with isolated SHFM. p63 mutations in SHFM included three novel mutations: a missense mutation (K193E), a nonsense mutation (Q634X), and a mutation in the 3' splice site for exon 5. The fourth SHFM mutation (R280H) in this series was also found in a patient with classical EEC syndrome, suggesting partial overlap between the EEC and SHFM mutational spectra. The original family with LMS (van Bokhoven et al. 1999) had no detectable p63 mutation, although it clearly localizes to the p63 locus in 3q27. In two other small kindreds affected with LMS, frameshift mutations were detected in exons 13 and 14, respectively. The combined data show that p63 is the major gene for EEC syndrome, and that it makes a modest contribution to SHFM. There appears to be a genotype-phenotype correlation, in that there is a specific pattern of missense mutations in EEC syndrome that are not generally found in SHFM or LMS.

Isolated bilateral anophthalmia in a girl with an apparently balanced de novo translocation: 46,XX,t(3;11)(q27;p11.2)

Primary anophthalmos is a heterogeneous condition. In its nonsyndromal form, it is usually considered an autosomal recessive trait. However, other causes such as chromosomal abnormalities and prenatal insults need to be considered. We report on a unique reciprocal translocation 46,XX,t(3;11)(q27;p11.2) in a baby with isolated anophthalmos. Both Chitayat et al. [1996] and Alvarez Arratia et al. [1984] have reported on cases of terminal deletion of the long arm of chromosome 3. In each case the child had multiple anomalies including microphthalmia or anophthalmia. Because our patient appears to have no other anomalies, this break point may indicate that a genetic locus for eye formation exists at chromosome site 3q27. Published 1999 Wiley-Liss, Inc.

Heterozygous germline mutations in the p53 homolog p63 are the cause of EEC syndrome

EEC syndrome is an autosomal dominant disorder characterized by ectrodactyly, ectodermal dysplasia, and facial clefts. We have mapped the genetic defect in several EEC syndrome families to a region of chromosome 3q27 previously implicated in the EEC-like disorder, limb mammary syndrome (LMS). Analysis of the p63 gene, a homolog of p53 located in the critical LMS/EEC interval, revealed heterozygous mutations in nine unrelated EEC families. Eight mutations result in amino acid substitutions that are predicted to abolish the DNA binding capacity of p63. The ninth is a frameshift mutation that affects the p63alpha, but not p63beta and p63gamma isotypes. Transactivation studies with these mutant p63 isotypes provide a molecular explanation for the dominant character of p63 mutations in EEC syndrome.

Interstitial deletion of band 3q25

Interstitial deletions of the long arm of chromosome 3 are rare. We report a man with an interstitial deletion involving band 3q25. To our knowledge, this is the first patient to be described with this cytogenetic abnormality.