Monozygotic twins concordant for Rubinstein-Taybi syndrome: changing phenotype during infancy

We describe monozygotic twin sisters concordant for Rubinstein-Taybi syndrome diagnosed at the age of 10 weeks. The typical features of Rubinstein-Taybi syndrome in early infancy increasingly developed towards the total "Gestalt" at the age of 2 years and 10 months.     

Monozygotic twins concordant for Rubinstein-Taybi syndrome and implications for genetic counseling

We report on a set of monozygotic twin boys concordant for Rubinstein-Taybi syndrome, and discuss the possible genetic basis of the disorder. © 1993 Wiley-Liss, Inc.     

Monozygotic twins discordant for the russell-silver syndrome

Russell-Silver syndrome (RSS) is a pattern of malformation characterized by intrauterine and postnatal growth retardation, limb asymmetry, triangular face, and hypospadias. We report on a patient, from a triplet pregnancy, who was one of identical male twins discordant for RSS. R.B. was a 710-g male born at 33 weeks of gestation, with hypospadias, chordee, and undescended testes. He had a normal 46,XY karyotype and no renal abnormalities. Female triplet A weighed 1,843 g, and male triplet B weighed 1,920 g. Both had normal physical findings and neonatal period. R.B. was first seen by us at age 6 7/12 years with short stature, triangular and asymmetric face, lower limb length discrepancy, and surgically repaired genital anomalies. Growth hormone testing results were normal. At age 8 7/12 years the brothers appeared physically identical except for size, with a height differential of 114.25 vs. 121.5 cm. Testing to establish biological zygosity was performed using VNTR (variable number tandem repeat) DNA probes YNH24 (D2S44), CMM101 (D14S13), EFD52 (D17S26), TBQ7 (D10S28), and 3′HVR (D16S85), PCR loci MCT118 (D1S80), and HLA-DQα. These data indicate a >99.99% probability of triplets B and C being monozygotic twins. While most occurrences of RSS are sporadic, familial cases suggesting autosomal dominance have been reported. Three other cases of probable monozygotic twins with RSS have been described. The significance of this confirmation of discordance in determining the cause of RSS is discussed. © 1995 Wiley-Liss, Inc.     

Monozygotic twins discordant for Ullrich-Turner syndrome

Ullrich-Turner syndrome occurred in one of a pair of female twins. The chromosome constitution of the affected twin was 45,X/46,XX and that of the normal twin 46,XX. Investigation of banded chromosomes, red cell antigens, HLA types, red cell enzymes, and serum proteins indicates monozygosity. The twins are discordant for height, pterygium colli, ovarian function, strabismus, dental eruption, external ear formation, hearing loss, and performance scores on the Wechsler Intelligence Test. All of these differences can be attributed to X monosomy in one cell line in the affected twin, presumably resulting from mitotic nondisjunction or anaphase lag early during embryonic development. Ten other pairs of apparently monozygotic twins discordant for the Ullrich-Turner syndrome have been reported previously, and the findings in these cases are reviewed.     

Monozygotic twins concordant for congenital short femur.

We report concordant male monozygotic twins with congenital short femur (proximal focal femoral deficiency) and discuss the aetiological implications. Coincidentally, they and their father have benign familial macrocephaly.     

Monozygotic twins discordant for spondylocostal dysostosis

Spondylocostal dysostosis (SCD) is a rare skeletal dysplasia with clinical and radiological manifestations, consisting of short neck and trunk, barrel-shaped chest, protuberant abdomen, scoliosis and abnormalities of vertebral segmentation and of the ribs. Both autosomal recessive and autosomal dominant inheritance have been described. We report on monozygotic twins discordant for the syndrome, either due to a post-zygotic mutation or development of a phenocopy. To our best knowledge, this is the fourth report of SCD in identical twins, and the first one of discordance in monozygotic twins. © 1994 Wiley-Liss, Inc.     

Apparent dominant transmission of the Rubinstein-Taybi syndrome

The cause of the Ruinstein-Taybi syndrome (RTS), a multiple congenital anomalies/mental retardation (MCA/MR) syndrome first described in 1963, remains obscure. Recently, a deletion of chromosomal material at 16p13.3 has been found in some patients with the disorder, but no such deletion can be identified in the majortity of affected individuals. Although the disorder has been well documented to be concordant in at least 7 monozygotic twin pairs and in one non-twin sib pair, only one clear-cut case of parent-to-child transmission has been reported previously. We present here a mother and daughter, both of whom appear to be affected with RTS, strongly suggesting either autosomal or X-linked dominant transmission. The paucity of previous cases of parent-to-child transmission may be related to either decreased fertility or decreased fitness in affected individuals. © 1993 Wiley-Liss, Inc.     

Monozygotic twins discordant for Proteus syndrome

Proteus syndrome is a rare, complex disorder predominantly characterized by asymmetric overgrowth of body parts, connective tissue and epidermal nevi, and vascular malformations. General diagnostic criteria comprise mosaic distribution, sporadic occurrence, and progressive course. We report on Proteus syndrome in discordant monozygotic twins. The affected 9-year-old boy showed progressive postnatal overgrowth of his right leg and foot and asymmetric progressive overgrowth of single toes with a small cerebriform connective tissue nevus on his right fourth toe. The progressive course was documented by serial photographs over a period of 3 years. Twin monozygosity was determined by PCR-amplified short tandem repeat (STR) analysis, revealing complete concordance of all alleles in both twins. This observation, to our knowledge, is only the second case report of discordant Proteus syndrome in monozygotic twins. This supports the hypothesis that this rare condition is caused by a postzygotic mutational event resulting in mosaicism.     

Monozygotic twins discordant for Ullrich-Turner syndrome

We describe 9-year-old twin girls who were thought to be monozygotic but who differed greatly in physical appearance and growth pattern. One twin had Ullrich-Turner syndrome (UTS), 45,X/46,XX mosaicism in peripheral blood, and only 45,X cells in skin fibroblasts. The phenotypically normal twin also had 45,X/46,XX mosaicism in blood but only 46,XX cells in cultured fibroblasts. Analysis of DNA marker patterns in blood lymphocytes and in skin fibroblasts confirmed monozygosity with a probability of 99.97%. This case is compared with other reported cases of discordance for UTS in twins. It is concluded that essentially all of the differences between the two twins can be explained by loss of an X chromosome early in embryogenesis with complete separation of 45,X and 46,XX cell lineages at the time of the twinning event. The presence of mosaicism in the peripheral blood of both twins is presumably due to anastomoses between the placentae resulting in a mixture of the two cell populations in the hematopoietic tissue.     

Monozygotic twinning and Wiedemann-Beckwith syndrome

Monozygotic (MZ) twinning occurs with relatively high frequency in Wiedemann-Beckwith syndrome (WBS). Ten sets of MZ twins with WBS have been reported. Nine of these have been female and in each case the twins were discordant for the WBS phenotype. The tenth set was male. They were concordant for WBS and both had a duplication of chromosome 15 which they shared in common with their phenotypically normal mother. The WBS gene has been asigned to the locus 11p15 and there appear to be several different genetic mechanisms involving this locus which all give rise to WBS. An imprinting effect for the WBS gene has been proposed because of the transmission of the gene preferentially through the maternal line in some large pedigrees. We describe two further sets of female M7 twins with WBS. One pair is concordant and one discordant for the condition. The possible genetic mechanisms involved in the expression of WBS are discussed, with particular reference to twinning, genomic imprinting and X-inactivation which is thought to be associated with the occurrence of MZ twinning in females.     

Monozygotic twins concordant for probable Alzheimer disease and increased platelet membrane fluidity

This report describes monozygotic twins who were concordant for probable Alzheimer disease, as defined by currently-accepted clinical criteria. Monozygosity was established by blood typing. Their ages of symptomatic onset were 57 and 66 yr, and the times from onset to institutionalization were 8 and 2 yr, respectively. These results suggest that age at onset and rate of progression are clinical features that can be affected by random processes or exposure to environmental factors. The platelet membrane fluidity of both twins was abnormally increased, and the respective values were identical within experimental limits. This result is consistent with published data suggesting that increased platelet membrane fluidity is associated with a clinically distinct subtype of Alzheimer disease and that this platelet membrane characteristic may be genetically determined.     

Monozygotic twins discordant for the Russell-Silver syndrome

Russell-Silver syndrome is a disorder of unknown cause. A number of familial cases have suggested autosomal dominant inheritance. We report on monozygotic twins discordant for the Russell-Silver syndrome. Our findings suggest that the cause of Russell-Silver syndrome is not explained entirely by genetic factors. The possible role of the intrauterine environment as an etiologic component of Russell-Silver syndrome is discussed.     

Monozygotic twins discordant for rubinstein-taybi syndrome.

A pair of male monozygotic twins discordant for Rubinstein-Taybi syndrome is reported. Monozygosity of the twins was established using blood grouping, typing of serum proteins, isozymes, HLA, and chromosomal heteromorphisms. The twins are the first twin pair discordant for the syndrome in which monozygosity has been firmly established. The pathogenesis of the syndrome is discussed in relation to the occurrence of both discordant and concordant monozygotic twins.     

Monozygotic twins discordant for Aicardi syndrome.

Aicardi syndrome is a developmental disorder characterised by agenesis of the corpus callosum, retinal lacunae, seizures, and developmental delay. It is believed to be X linked with lethality in males. We report a set of monozygotic female twins one of whom is healthy and intellectually normal while the other has the classical Aicardi phenotype with profound retardation. Family history is negative. Both had normal karyotypes. Monozygosity was established by blood grouping, chromosomal heteromorphisms, and DNA analysis using six hypervariable probes (five autosomal and one X linked) and three X linked RFLP probes. We tested the hypothesis that preferential inactivation of a different X chromosome had occurred in each girl. Methylation sensitive RFLP analysis of DNA from EBV transformed B lymphocytes and cultured skin fibroblasts using MspI/HpaII digestion and probing with M27 beta showed a very similar pattern of X inactivation in both twins with no evidence of preferential expression of one particular X chromosome. We conclude that the abnormalities in the affected twin are probably the consequence of a postzygotic mutation in early embryonic development.