Rubinstein-Taybi syndrome: further evidence of a genetic aetiology

Inheritance and variable expression in Rubinstein-Taybi syndrome

Familial Rubinstein-Taybi syndrome (RTS) is very rare. Here we report on the 6th and 7th case of inherited RTS. Family 1 presents with incomplete or mild RTS over three generations; a 13-year-old girl (proband 1) with mild but typical facial features and learning disabilities, her very mildly affected mother (proband 2), and the maternal grandmother (proband 3). Family 2 includes three females with classical RTS (probands 4-6) and their father (proband 7) with broad thumbs and halluces. Proband 5 also had a brain tumor (ganglioglioma) at the age of 3 years. In probands 1-3, direct sequencing identified a novel CREBBP missense mutation, c.2728A > G (predicting p.Thr910Ala), that was absent in non-affected family members. The p.Thr910Ala variant is outside the crucial histone acetyltransferase domain, and this may explain the mild and variable phenotype. In probands 4-7 we identified another novel CREBBP mutation, c.4134G > T, which alters the consensus splice sequence at position 1 of exon 25. The c.4134G > T mutation was transmitted from the very mildly affected father who displayed somatic mosaicism (with 38% mutated alleles in blood and 31% in buccal smear DNA) to his three daughters. Our findings emphasize that variable expression (family 1) and somatic mosaicism (family 2) contribute to the phenotypic variability of RTS. Somatic mosaicism may be more frequent in RTS than previously assumed. Accumulating data suggest a recurrence risk of approximately 0.5-1% for parents of a child with RTS, exceeding the so far estimated risk of approximately 0.1% for siblings.

Etiology and recurrence risk in Rubinstein-Taybi syndrome

Epidemiologic data on 45 patients with Rubinstein-Taybi syndrome from the Netherlands and 50 patients from the USA are compared with data from 407 patients reported in the literature. The 502 probands had a total of 708 sibs, including one probable recurrence. In 12 of 13 proven or possible monozygotic twins both children were affected. Two patients have reproduced with one affected and 2 normal offspring. The empiric recurrence risk figure for sibs is 0.1%. The recurrence risk for offspring of affected individuals could be as high as 50%. The cause of the syndrome remains unknown. There were no clues for autosomal recessive or X-linked inheritance, nor for a teratogenic cause. No consistent chromosome anomaly was found. An autosomal dominant mutation, either as submicroscopic chromosome deletion or duplication, or a point mutation seems the most likely explanation.

Broad thumb-hallux (Rubinstein-Taybi) syndrome 1957-1988

This presentation records the early history of the description of the broad thumb-hallux syndrome and attempts to update the current state of knowledge about this syndrome. Information was collected and reviewed on 571 individuals from the world literature, from communications with colleagues and families of affected individuals, and from personal observation. The diagnosis was established in most cases by confirming the concurrence of the constellation of major diagnostic criteria, including broad short terminal phalanges of the thumbs and halluces, with or without angulation deformity; characteristic facial appearance with beaked or straight nose, antimongoloid slant of palpebral fissures, apparent or clinical hypertelorism and grimacing smile; stature and head circumference (OFC) below 50th centile; mental, motor, social, and language retardation; stiff awkward gait; and incomplete or delayed descent of testes in males. Information on associated clinical factors, familial occurrence, and cytogenetic findings is presented.

Apparent dominant transmission of the Rubinstein-Taybi syndrome

The cause of the Rubinstein-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 majority 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.

Monozygotic twins concordant for Rubinstein-Taybi syndrome

Monozygotic twin sisters from Qatar, concordant for the Rubinstein-Taybi syndrome, are described. Skeletal anomalies not previously seen in this syndrome are described. The mode of inheritance is reviewed.

Rubinstein-Taybi syndrome in a mother and son

The Rubinstein-Taybi syndrome is a condition characterized by mental retardation, typical facial changes and broad thumbs and big toes. The cause is unknown; almost all cases are sporadic. We describe a mother and son with Rubinstein-Taybi syndrome. Literature search documented at least 413 cases with 558 sibs. An affected offspring has occurred at least twice, possibly six times. In 45 yet undescribed Dutch cases no recurrence was found in 94 sibs. A submicroscopic chromosome deletion seems the most probable explanation, but other alternatives may be possible.

Prenatal diagnosis of Wiedemann-Beckwith syndrome

We report the prenatal diagnosis of Wiedemann-Beckwith syndrome in the 28th week of pregnancy in a primigravida. The cause of hospitalization was severe polyhydramnios with premature labour. Sonography revealed macrosomia, nephromegaly, cysts of adrenal glands and a striking macroglossia with opened mouth in all controls. The combination of all these symptoms suggested the prenatal diagnosis of Wiedemann-Beckwith syndrome, which could be confirmed post partum after a normal delivery in the 33rd week of pregnancy. The newborn (2700 g, 48 cm) exhibited typical features of this syndrome as moderate hypoglycemia and polycythemia in addition to the sonographic finding. Pathogenetic aspects and differential diagnosis of macrosomia are discussed.

Rubinstein-Taybi syndrome

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