Large deletions encompassing the TCOF1 and CAMK2A genes are responsible for Treacher Collins syndrome with intellectual disability

Mandibulofacial dysostosis is part of a clinically and genetically heterogeneous group of disorders of craniofacial development, which lead to malar and mandibular hypoplasia. Treacher Collins syndrome is the major cause of mandibulofacial dysostosis and is due to mutations in the TCOF1 gene. Usually patients with Treacher Collins syndrome do not present with intellectual disability. Recently, the EFTUD2 gene was identified in patients with mandibulofacial dysostosis associated with microcephaly, intellectual disability and esophageal atresia. We report on two patients presenting with mandibulofacial dysostosis characteristic of Treacher Collins syndrome, but associated with unexpected intellectual disability, due to a large deletion encompassing several genes including the TCOF1 gene. We discuss the involvement of the other deleted genes such as CAMK2A or SLC6A7 in the cognitive development delay of the patients reported, and we propose the systematic investigation for 5q32 deletion when intellectual disability is associated with Treacher Collins syndrome.     

Mosaicism of a TCOF1 mutation in an individual clinically unaffected with Treacher Collins syndrome

Treacher Collins syndrome (TCS) or mandibulofacial dysostosis is an autosomal dominant disorder of craniofacial development with 60% of its cases arising de novo. Other modes of inheritance such as autosomal recessive, gonadal mosaicism, and chromosomal rearrangement have also been proposed. This syndrome can result from TCOF1 gene mutations. In this study we identified a TCOF1 1408delAG heterozygous mutation in a patient with the clinical diagnosis of TCS. This same mutation was found in the clinically unaffected mother's leukocytes, hair root bulbs, buccal mucosa, urine, and stool. The mother has a clinically unaffected child and the maternal grandparents do not have the mutation. Because the mother has the mutation in cells derived from all three germ layers, we suspected the mutation was nonpenetrant. However, we could not detect the mutation in her skin fibroblasts, suggesting she is mosaic secondary to cell type specific selection.     

Evidence of a locus for orofacial clefting on human chromosome 6p24 and STS content map of the region

Orofacial clefting is genetically complex, no single gene beingresponsible for all forms. It can, however, result from a singlegene defect either as part of a syndrome (e.g. van der Woudesyndrome, Treacher—Colllns syndrome, velo–cardio–facialsyndrome) or as an Isolated phenotypic effect (e.g. X–linkedcleft palate; non–syndromlc, autosomal dominant orofacialclefting). Several studies have suggested that chromosome 6pis a candidate region for a locus involved in orofacial clefting.We have used YAC clones from contigs in 6p25–p23 to investigatethree unrelated cases of cleft lip and palate coincident withchromosome 6p abnormalities. Case 1 has bilateral cleft lipand palate and a balanced translocation reported as 46, XY,t(6, 7)(p23; q36.1). Case 2 has multiple abnormalities Includingcleft lip and palate and was reported as 46, XX, del(6)(p23;pter). Case 3 has bilateral cleft lip and palate and carriesa balanced translocation reported as 46, XX, t(6; 9)(p23;q22.3).We have Identified two YAC clones, both of which cross the breakpointin cases 1 and 3 and are deleted in case 2. These clones mapto 6p24.3 and therefore suggest the presence of a locus fororofacial clefting in this region. The HGP22 and AP2 genes,potentially involved in face formation, have been found to flankthis region, while F13A maps further telomeric in 6p24.3/25.     

Treacher Collins syndrome: a clinical and molecular study based on a large series of patients

PurposeTreacher Collins/Franceschetti syndrome (TCS; OMIM 154500) is a disorder of craniofacial development belonging to the heterogeneous group of mandibulofacial dysostoses. TCS is classically characterized by bilateral mandibular and malar hypoplasia, downward-slanting palpebral fissures, and microtia. To date, three genes have been identified in TCS:,TCOF1, POLR1D, and POLR1C.MethodsWe report a clinical and extensive molecular study, including TCOF1, POLR1D, POLR1C, and EFTUD2 genes, in a series of 146 patients with TCS. Phenotype–genotype correlations were investigated for 19 clinical features, between TCOF1 and POLR1D, and the type of mutation or its localization in the TCOF1 gene.ResultsWe identified 92/146 patients (63%) with a molecular anomaly within TCOF1, 9/146 (6%) within POLR1D, and none within POLR1C. Among the atypical negative patients (with intellectual disability and/or microcephaly), we identified four patients carrying a mutation in EFTUD2 and two patients with 5q32 deletion encompassing TCOF1 and CAMK2A in particular. Congenital cardiac defects occurred more frequently among patients with TCOF1 mutation (7/92, 8%) than reported in the literature.ConclusionEven though TCOF1 and POLR1D were associated with extreme clinical variability, we found no phenotype–genotype correlation. In cases with a typical phenotype of TCS, 6/146 (4%) remained with an unidentified molecular defect.     

Sporadic, idiopathic MCA syndrome with mandibulofacial dysostosis and tibial hemimelia.

We report on a Brazilian woman with mandibulofacial dysostosis, cleft lip/palate, vertebral anomalies, abnormally modeled femora, and bilateral tibial agenesis. The clinical aspects involving this patient strongly suggest an unreported condition. Clinical and genetic aspects are discussed.     

Median cleft of upper lip and pedunculated skin masses associated with de novo reciprocal translocation 46,X,t(X;16)(q28;q11.2).

We describe a de novo apparently balanced reciprocal translocation, 46,X,t(X;16)(q28;q11.2), in a 13 year old girl with median cleft of the upper lip, pedunculated skin masses on the nasal septum, short stature, and mental retardation. Pai syndrome is characterised by median cleft of the upper lip, pedunculated skin mass(es) on the face, and midline lipoma(s) of the central nervous system. The cause of this syndrome is unknown, although autosomal dominant inheritance has been proposed. The translocation breakpoints in the present patient may be candidate regions for a gene responsible for median cleft of the upper lip and pedunculated skin mass(es) on the face, including Pai syndrome.     

Sporadic,idiopathic MCA syndrome with mandibulofacial dysostosis and tibial hemimelia

We report on a Brazilian woman with mandibulofacial dysostosis, cleft lip/palate, vertebral anomalies, abnormally modeled femora, and bilateral tibial agenesis. The clinical aspects involving this patient strongly suggest an unreported condition. Clinical and genetic aspects are discussed.     

Autosomal recessive Treacher Collins syndrome due to POLR1C mutations: Report of a new family and review of the literature

Treacher Collins syndrome (TCS) is a frequent cause of mandibulofacial dysostosis. To date, TCS‐causing mutations in three genes, namely TCOF1, POLR1D, and POLR1C have been identified. TCS is usually inherited in an autosomal dominant manner, with a high clinical variability and no phenotype–genotype correlation. Up‐to now, five families have been reported with an autosomal recessive mode of inheritance due to mutations in POLR1D or POLR1C. We report here a new family with two sisters affected by mild TCS carrying compound POLR1C heterozygous mutations, and review the literature on mild forms of TCS, autosomal recessive inheritance in this syndrome and POLR1C mutations.     

Acrofacial dysostosis (Nager syndrome): Synopsis and report of a new case

Acrofacial dysostosis is noted in a stillborn female with mandibulofacial abnormality without cleft palate and with bilateral radial hemimelia, duplication of the left great toe, and aplasia of the right kidney. Synopsis of the published cases shows that the various degrees of mandibulofacial dysostosis frequently characterized by cleft palate and atresia of the auditory meatus are not closely correlated with the malformation of the upper limb. Formal genetics are unknown.     

Mild mandibulofacial dysostosis in a child with a deletion of 3p

We report on a patient with mild mandibulofacial dysostosis and a small interstitial deletion of 3p,46,XY,del(3)(p23p24.12). Linkage of Treacher Collins syndrome, the most common of the mandibulofacial dysostosis, to the 5q31.3→q33.3 region of chromosome 5 has been established. This is the fourth report of a patient with mandibulofacial dysostosis with a chromosome abnormality outside the 5q31.3 area. Mandibulofacial dysostosis is a heterogeneous entity, and evaluation and counseling of affected individuals should be undertaken with caution. © 1993 Wiley-Liss, Inc.     

Syndrome of acrofacial dysostosis,cleft lip/palate,and triphalangeal thumb in a brazilian family

We describe two daughters of a nonconsanguineous couple. Both had facial and skeletal anomalies, but in quantitatively and qualitatively different ways. In one patient signs of mandibulofacial dysostosis are associated with anomalies of the radial rays of both arms. In the other, cleft lip and cleft palate are associated with hypoplastic thumbs. Clinical and genetical aspects of present case are discussed.     

POLR1B and neural crest cell anomalies in Treacher Collins syndrome type 4

PurposeTreacher Collins syndrome (TCS) is a rare autosomal dominant mandibulofacial dysostosis, with a prevalence of 0.2–1/10,000. Features include bilateral and symmetrical malar and mandibular hypoplasia and facial abnormalities due to abnormal neural crest cell (NCC) migration and differentiation. To date, three genes have been identified: TCOF1, POLR1C, and POLR1D. Despite a large number of patients with a molecular diagnosis, some remain without a known genetic anomaly.MethodsWe performed exome sequencing for four individuals with TCS but who were negative for pathogenic variants in the known causative genes. The effect of the pathogenic variants was investigated in zebrafish.ResultsWe identified three novel pathogenic variants in POLR1B. Knockdown of polr1b in zebrafish induced an abnormal craniofacial phenotype mimicking TCS that was associated with altered ribosomal gene expression, massive p53-associated cellular apoptosis in the neuroepithelium, and reduced number of NCC derivatives.ConclusionPathogenic variants in the RNA polymerase I subunit POLR1B might induce massive p53-dependent apoptosis in a restricted neuroepithelium area, altering NCC migration and causing cranioskeletal malformations. We identify POLR1B as a new causative gene responsible for a novel TCS syndrome (TCS4) and establish a novel experimental model in zebrafish to study POLR1B-related TCS.     

Two cases with interstitial deletions of chromosome 2 and sex reversal in one.

We present two children with de novo interstitial deletions of the long arm of chromosome 2 (karyotypes 46,XY, del(2)(q31.1q31.3) and 46,XY, del(2)(q24.3q31.3), respectively). The first child had severe learning difficulties, growth retardation, unilateral ptosis, small palpebral fissures, a cleft uvula, and bilateral cutaneous syndactyly of the second and third toes. Despite her male karyotype, she had female external genitalia with hypoplasia of the clitoris and labia minora. This is the first reported case of feminization of the external genitalia in a genotypic male with an interstitial deletion of chromosome 2q31 and adds to the growing amount of evidence for a gene involved in sex determination in this chromosome region. The second child had severe mental and growth retardation, ptosis, down-slanting palpebral fissures, low-set ears, micrognathia, finger camptodactyly, and brachysyndactyly of the second to fifth toes. The clinical manifestations associated with deletions of 2q31 to 2q33 are similar to those found with proximal deletions at 2q24 to 2q31 and of band 2q24, suggesting that the phenotype may result from haploinsufficiency for one or more genes located at 2q31. Microsatellite marker studies showed that both children had paternally derived deletions that included the HOXD gene cluster and the EVX2, DLX1, and DLX2 genes known to be important in limb development.     

Fetus with two identical reciprocal translocations: description of a rare complication of consanguinity

We report on a 24-week fetus with multiple organ anomalies secondary to biparental inheritance of an apparently balanced t(17;20) reciprocal translocation. The pregnancy was terminated following the discovery by ultrasound of an abnormal heart and micrognathia. At autopsy, the following anomalies were found: Pierre-Robin sequence, hypoplasia of the right ventricle with muscular hypertrophy, and endocardial fibroelastosis, hypoplastic lungs, dysplastic left kidney, bilateral pelvicalyceal dilatation, central nervous system periventricular heterotopias and right sided club foot. Given the endocardial fibroelastosis and cleft palate, Eastman-Bixler syndrome (Facio-cardio-renal) is a possible diagnosis. The parents were first cousins and each had an identical t(17;20)(q21.1;p11.21) translocation. The fetal karyotype was 46,XX,t(17;20)(q21.1;p11.21)mat,t(17;20)(q21.1;p11.21)pat. While there are a few reports of consanguineous families where both the mother and father had the same reciprocal translocation and offspring with unbalanced karyotypes, we were unable to find any reports of a fetus/child with double identical reciprocal translocations. We propose that although the fetus had an apparently balanced karyotype, inheriting only the translocated chromosomes led to the unmasking of a recessive syndrome. It seems most likely that a gene (or genes) was disrupted by the breaks but the parents might also be heterozygous carriers of a recessive gene mutation since the fetus must be homozygous by descent for many loci on both chromosomes 17 and 20 (as well as on other chromosomal segments). It was not possible to totally exclude segmental uniparental disomy as a cause of the anomalies as no recombinations were detected for chromosome 17. However, there is no evidence to suggest that chromosome 17 is imprinted and UPD 20 was excluded thus making an imprinting error unlikely.     

Duplication of distal 17q: Report of an observation

We describe a boy with the syndrome due to dup(17q) resulting from a paternal balanced t(12;17) (q24;q23). The comparison of the clinical findings in our patient with those previously reported shows that the dup(17q23 → qter) is associated with a clinically recognizable syndrome. Anomalies present in ≥ 75% of the patients were severe psychomotor retardation; short stature; microcephaly; frontal bossing and temporal retraction; widow's peak; narrow palpebral fissures; flat nasal bridge; thin upper lip overlapping thin lower lip; downturned corners of the mouth; apparently low-set, posteriorly angulated and malformed ears; low posterior hairline; widely spaced nipples; cryptorchidism; proximal limb shortness; and hyperlaxity of limb joints. The translocation carrier father of our patient had a Poland anomaly.     

Brief clinical report: duplication of distal 17q: report of an observation

We describe a boy with the syndrome due to dup(17q) resulting from a paternal balanced t(12;17) (q24;q23). The comparison of the clinical findings in our patient with those previously reported shows that the dup(17q23----qter) is associated with a clinically recognizable syndrome. Anomalies present in greater than or equal to 75% of the patients were severe psychomotor retardation; short stature; microcephaly; frontal bossing and temporal retraction; widow's peak; narrow palpebral fissures; flat nasal bridge; thin upper lip overlapping thin lower lip; downturned corners of the mouth; apparently low-set, posteriorly angulated and malformed ears; low posterior hairline; widely spaced nipples; cryptorchidism; proximal limb shortness; and hyperlaxity of limb joints. The translocation carrier father of our patient had a Poland anomaly.     

Deletion of chromosome 2q24-q31 causes characteristic digital anomalies: Case report and review

We describe a newborn boy with multiple anomalies, including bilateral split foot and an interstitial deletion of chromosome 2 (q24.2-q31.1). Four additional cases in 2 families involving similar deletions have been reported. Bilateral digital anomalies of hands and feet were seen in all 5 cases, including a wide cleft between the first and second toes, wide halluces, brachysyndactyly of the toes, and camptodactyly of the fingers. Other common manifestations have included postnatal growth and mental retardation, microcephaly, down-slanting palpebral fissures, micrognathia, and apparently low-set ears. Bilateral digital anomalies were reported in 22 of 24 cases with deletions including at least part of region 2q24-q31. Digital anomalies were not prevalent in 18 patients with deletions of chromosome 2q not overlapping 2q24-q31. 2q31.1 appears to be the common deleted segment in all cases with significant digital anomalies, which implies the existence of one or more genes involved in distal limb morphogenesis in this region. HOXD13 and EVX2, located in the proximity of 2q31, were not deleted in our patient by Southern analysis. Bilateral digital malformations of the hands and feet associated with other anomalies should be evaluated by chromosome analysis focused at the 2q24-q31 region. © 1995 Wiley-Liss, Inc.     

Identification of mutations in TCOF1: use of molecular analysis in the pre- and postnatal diagnosis of Treacher Collins syndrome

Treacher Collins syndrome (TCS) is an autosomal dominant disorder of facial development, which results from mutations in TCOF1. TCS comprises conductive hearing loss, hypoplasia of the mandible and maxilla, downward sloping palpebral fissures and cleft palate. Although, there is usually a reasonable degree of bilateral symmetry, a high degree of both inter- and intrafamilial variability is characteristic of TCS. The wide variation in the clinical presentation of different patients, together with the fact that more than 60% of cases arise de novo, can complicate the diagnosis of mild cases and genetic counselling. In the current study, we describe how molecular techniques have been used to facilitate pre- and postnatal disease diagnoses in 13 TCS families.     

Translocation breakpoint at 7q31 associated with tics: further evidence for IMMP2L as a candidate gene for Tourette syndrome

Gilles de la Tourette syndrome is a complex neuropsychiatric disorder with a strong genetic basis. We identified a male patient with Tourette syndrome-like tics and an apparently balanced de novo translocation [46,XY,t(2;7)(p24.2;q31)]. Further analysis using array comparative genomic hybridisation (CGH) revealed a cryptic deletion at 7q31.1-7q31.2. Breakpoints disrupting this region have been reported in one isolated and one familial case of Tourette syndrome. In our case, IMMP2L, a gene coding for a human homologue of the yeast inner mitochondrial membrane peptidase subunit 2, was disrupted by the breakpoint on 7q31.1, with deletion of exons 1-3 of the gene. The IMMP2L gene has previously been proposed as a candidate gene for Tourette syndrome, and our case provides further evidence of its possible role in the pathogenesis. The deleted region (7q31.1-7q31.2) of 7.2 Mb of genomic DNA also encompasses numerous genes, including FOXP2, associated with verbal dyspraxia, and the CFTR gene.