Holoprosencephaly in monozygotic twins - clinical and computer tomographic findings

Some causes of genotypic and phenotypic discordance in monozygotic twin pairs

The use of the adjective "identical" rather than monozygotic leads to misunderstandings about the biology of monozygotic twinning. Most monozygotic twin pairs are not identical; there may be major discordance for birth weight, genetic disease, and congenital anomalies. These indicate that postzygotic events may lead to the formation of two or more cell clones in the inner cell mass and early embryo that actually stimulate the monozygotic twinning event. There is also evidence that there may be unequal allocation of numbers of cells to the monozygotic twins; this may have widespread implications for the cascade of developmental events during embryogenesis, formation, and vascularization of the placenta. Large-scale zygosity testing at birth could be the template for analysis of twin outcomes and their biologic causes.

Holoprosencephaly: a family showing dominant inheritance and variable expression

A family with probable dominant holoprosencephaly is presented with five affected subjects in two sibships, the offspring of healthy sisters who are presumed gene carriers. Of the affected children, three had cebocephaly and died shortly after birth. One had left choanal atresia, retinal coloboma, a single central maxillary incisor, microcephaly, short stature, and learning problems. Another had only a single central maxillary incisor. The occurrence of hypotelorism, microcephaly, and unilateral cleft lip and palate as minor manifestations of the gene in possible and probable gene carriers is discussed.

Definitive methods of zygosity determination in twins: relevance to problems in the biology of twinning

Many studies of embryogenesis and fate of twin pregnancies are invalidated because zygosity is not determined definitively, or is assumed on the basis of inadequate criteria. This paper briefly reviews methods of zygosity determination. It reports published results and a new series of twins in which zygosity was determined by DNA fingerprinting. Implications for methods of prenatal diagnosis of zygosity are discussed in the context of the occasional need for intervention in twin transfusion syndrome or in twins discordant for major malformations. Definitive zygosity and placental anatomy (number of chorions and amnions) is discussed as the firm substrate for studies of normal and abnormal twin development.

Perspectives on holoprosencephaly: Part I. Epidemiology, genetics, and syndromology

This paper provides an updated, comprehensive, critical review of the epidemiology, genetics, and syndromic aspects of holoprosencephaly and is divided into four parts. In the first part, epidemiologic aspects are discussed under the following headings: prevalence, temporal trends, socioeconomic status, exposure to environmental teratogens, maternal and paternal ages, pregnancy histories, and birth weights. The second part analyzes the facial phenotypes because the genetic and syndromic aspects of holoprosencephaly cannot be understood without knowledge of facial variability and its meaning. Topics discussed include cyclopia, ethmocephaly, cebocephaly, median cleft lip, and less severe facial dysmorphism. The third section, on genetics, analyzes associated anomalies, chromosomal and non-chromosomal holoprosencephaly, family studies, twin studies, genetics of nonsyndromic holoprosencephaly, and recurrence risks. The final section on syndromology summarizes 48 conditions in which some degree of holoprosencephaly may be a feature.

Microscopic study of holoprosencephalic facial anomalies in trisomy 13 fetuses

The cerebral and facial anatomy of four trisomy 13 fetuses was studied in order to delineate the varying degrees of expression of severity of holoprosencephaly. Fetal heads were serially sectioned and analyzed microscopically in the horizontal plane. Examples of cyclopia, cebocephaly, and a proposed new category, premaxillary dysgenesis, were studied. The last category represents the least severe end of the facial spectrum of holoprosencephaly in this series. In this condition, there are deficiencies or clefts within the premaxilla, in contrast to the usual site of clefting between the maxilla and the premaxilla. There is asymmetry of the defects in the anterior midface of all four cases.

Developmental Foix-Chavany-Marie syndrome in identical twins

Foix, Chavany, and Marie described a syndrome of faciopharyngoglossomasticatory diplegia resulting from bilateral anterior opercular infarction. We describe identical twins who have a developmental form of the syndrome. The twins, aged 41 years, were the product of a normal pregnancy and birth, but had subsequent delayed motor milestones, seizures, poor language development, mild mental retardation, drooling, absent gag reflexes, inability to protrude the tongue, brisk jaw jerks, impaired fine finger movements, symmetrical brisk reflexes, flexor plantar responses, and mildly spastic gait. Magnetic resonance imaging showed bilateral perisylvian cortical dysplasia compatible with polymicrogyria and incomplete opercular formation.

Velo-cardio-facial syndrome presenting as holoprosencephaly

A baby with holoprosencephaly and the tetralogy of Fallot is described. The mother had operative correction of the same cardiac lesion and shows features typical of the velo-cardio-facial syndrome, an autosomal dominant disorder. The association between holoprosencephaly and this condition has not been previously reported. When holoprosencephaly is found associated with congenital heart disease, velo-cardio-facial syndrome should be sought in other family members.

Monozygotic twin aborted fetuses discordant for holoprosencephaly/synotia

A pair of monozygotic twin fetuses aborted at 15 weeks were found to be discordant for holoprosencephaly and synotia. They were studied grossly, radiologically, and histologically. Features of first brancial arch dysplasia (synotia, agnathia, and astomia) and holoprosencephaly (absent ethmoid bone and Rathke's pouch) observed in one twin were contrasted with minimal dysmorphology in the co-twin. Some evidence of the twin transfusion syndrome was also apparent, perhaps contributing to the twins' spontaneous abortion.

Occurrence of cyclopia, myelomeningocele, deafness, and abducens paralysis in siblings

As holoprosencephaly without chromosome defect may be associated with other CNS-related anomalies such as mental retardation, mental illness, facial paralysis, endocrine disorders, deafness, spina bifida, and myelomeningocele, we present a family in which one girl had a myelomeningocele, a brother had orbital hypotelorism, facial and cerebral asymmetries, cerebral palsy, abducens paralysis, and inner ear deafness. A 3rd pregnancy was terminated at 16 weeks; the fetus had cyclopia. A common cause is discussed in these cases and in those families in which holoprosencephaly and additional malformations occur among different generations.