Recurrent Mutations in the Basic Domain of TWIST2 Cause Ablepharon Macrostomia and Barber-Say Syndromes.

Ablepharon macrostomia syndrome (AMS) and Barber-Say syndrome (BSS) are rare congenital ectodermal dysplasias characterized by similar clinical features. To establish the genetic basis of AMS and BSS, we performed extensive clinical phenotyping, whole exome and candidate gene sequencing, and functional validations. We identified a recurrent de novo mutation in TWIST2 in seven independent AMS-affected families, as well as another recurrent de novo mutation affecting the same amino acid in ten independent BSS-affected families. Moreover, a genotype-phenotype correlation was observed, because the two syndromes differed based solely upon the nature of the substituting amino acid: a lysine at TWIST2 residue 75 resulted in AMS, whereas a glutamine or alanine yielded BSS. TWIST2 encodes a basic helix-loop-helix transcription factor that regulates the development of mesenchymal tissues. All identified mutations fell in the basic domain of TWIST2 and altered the DNA-binding pattern of Flag-TWIST2 in HeLa cells. Comparison of wild-type and mutant TWIST2 expressed in zebrafish identified abnormal developmental phenotypes and widespread transcriptome changes. Our results suggest that autosomal-dominant TWIST2 mutations cause AMS or BSS by inducing protean effects on the transcription factor's DNA binding.

Evidence for autosomal dominant inheritance of ablepharon-macrostomia syndrome.

Ablepharon-macrostomia syndrome (AMS) is characterized by absent or short eyelids, macrostomia, ear anomalies, absent lanugo and hair, redundant skin, abnormal genitalia, and developmental delay in two-thirds of the reported patients. Additional anomalies include dry skin, growth retardation, hearing loss, camptodactyly, hypertelorism, absent zygomatic arches, and umbilical abnormalities. We present the second familial case of ablepharon-macrostomia syndrome in a newborn female and her 22-year-old father making autosomal dominant inheritance more likely than the previously proposed autosomal recessive transmission for this disorder. These cases likely represent the 16th and 17th reported cases of AMS and the first case suspected on prenatal ultrasound. Additionally, the child shows more prominent features of the disorder when compared to her father documenting variable expression and possible anticipation.

Barber-Say Syndrome and Ablepharon-Macrostomia Syndrome: A Patient's View.

Barber-Say syndrome (BSS) and ablepharon-macrostomia syndrome (AMS) are infrequently reported congenital malformation disorders caused by mutations in the TWIST2 gene. Both are characterized by abnormalities in ectoderm-derived structures and cause a very unusual morphology of mainly the face in individuals with otherwise normal cognition and normal physical functioning. We studied the impact that the presence of BSS and AMS has on psychosocial functioning of affected individuals and their families, using their point of view to start with. We tabulated frequently asked questions from affected individuals and families, and a parent of an affected child and an affected adult woman offered personal testimonies. We focused on perception of illness, body satisfaction, and the consequences for an otherwise normal individual who has a disorder that interferes with body image. The importance of paying particular attention to the management of both the physical appearance and the consequences of these entities on the quality of life is stressed by the affected individuals themselves.

Molecular analysis of nondisjunction in mice heterozygous for a Robertsonian translocation.

A Robertsonian translocation results in a metacentric chromosome produced by the fusion of two acrocentric chromosomes. Rb heterozygous mice frequently generate aneuploid gametes and embryos, providing a good model for studying meiotic nondisjunction. We intercrossed mice heterozygous for a (7.18) Robertsonian translocation and performed molecular genotyping of 1812 embryos from 364 litters with known parental origin, strain, and age. Nondisjunction events were scored and factors influencing the frequency of nondisjunction involving chromosomes 7 and 18 were examined. We concluded the following: 1. The frequency of nondisjunction among 1784 embryos (3568 meioses) was 15.9%. 2. Nondisjunction events were distributed nonrandomly among progeny. This was inferred from the distribution of the frequency of trisomics and uniparental disomics (UPDs) among all litters. 3. There was no evidence to show an effect of maternal or paternal age on the frequency of nondisjunction. 4. Strain background did not play an appreciable role in nondisjunction frequency. 5. The frequency of nondisjunction for chromosome 18 was significantly higher than that for chromosome 7 in males. 6. The frequency of nondisjunction for chromosome 7 was significantly higher in females than in males. These results show that molecular genotyping provides a valuable tool for understanding factors influencing meiotic nondisjunction in mammals.