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PURPOSE: The aim of the study was to analyze the frequency and certain epidemiological characteristics of a consecutive series of conjoined twins born in Spain. MATERIAL AND METHODS: We used data from the Spanish Collaborative Study of Congenital Malformations for the period April 1976 to 2006. Because the Spanish law permitting voluntary termination of pregnancies (TOP) when the fetus presented malformations was effective by the end of 1985, we analyzed the data in 4 periods, 2 before 1986 and 2 after. During the first period (1976-1979) only live births were recorded, whereas both still and live births were included in the other three (1980-1985, 1986-1995, and 1996-2006). In the present study, the cases were classified as symmetrical (16 pairs) and asymmetrical (1 pair) conjoined twins. Each pair of conjoined twins was considered as only one case for calculations, regardless of the type of union. RESULTS: Among a total of 2,281,604 consecutive births between 1980 and 2006, there were a total of 15 cases of symmetrical conjoined twins giving a frequency of 0.70 per 100,000 (1/152,107), whereas there was only 1 stillborn asymmetrical conjoined twin pair (0.04/100,000). Among the 13,418 consecutive stillborns surveyed, 6 cases of conjoined twins were identified (either symmetrical or asymmetrical) giving a frequency of 44.72 per 100,000, and 11 pairs were identified among the 2,425,583 total live births surveyed during the first period 1976 to 1979, a frequency of 0.45 per 100,000. Thus, the frequency among stillborn infants is 99.34 times higher than that observed among live births. However, the frequency for the total births (3 last periods) showed a decreasing trend from 1.47 per 100,000 birth in the first period (1980-1985) when TOP was illegal, to a value of 0.09 per 100,000 in the last period, more than 16-fold lower, probably because of the TOP of affected fetuses. Therefore, we consider that the frequencies observed in the period 1980 to 1985 are the basal values in our population. The most frequent type observed was thoracopagus, with an overall prevalence at birth of 0.44 per 100,000 (1/228,160) from 1980 to 2006, representing 58.82% of the total population of symmetric conjoined twin pairs. Diprosopus pairs were the next most common group (11.76%). Most of the cases were females (4 males/11 females), and although this appeared to be mainly because of the thoracopagus pairs (males-females, 2:8), in such a small number of cases, it is not possible to determine the ratios for the other groups. Gestational age was significantly shorter than in control twins for each type studied. CONCLUSIONS: We conclude that it is incorrect to consider that all types of conjoined twins have the same epidemiological characteristics, such as the frequency at birth. The differences observed may be related with the distinct embryo-fetal mortality of each type of conjoined twins in different populations, and the sex ratio, among others.

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Craniofacial dyssynostosis (CD) is characterized by premature fusion of the lambdoid and posterior part of the sagittal sutures, and short stature. Thus, the skull shape becomes dolichocephalic with protuberant forehead and either bulging or flat occiput. Facial changes are secondary to the skull defects, and some additional findings have also been described. We report on the first four known Spanish patients. They were unrelated and had Spanish ancestors. In the three previous reports about this syndrome, the authors hypothesized that the frequency of the gene causing CD must be rather high in the Spanish population, and relatively common in areas with Spanish ancestry. We have estimated the minimal birth prevalence of the syndrome in 0.51 per million livebirths. It has been previously suggested that the syndrome is inherited as an autosomal recessive trait, since there were two affected sisters among the nine published cases. Phenotypic variability is discussed in detail in this paper. We also underline several aspects for the anticipatory guidance of affected individuals, especially recommending a neurologic evaluation taking into account the radiologic findings in order to plan early interventions to avoid undesirable consequences of craniosynostosis. It is also recommended to perform additional studies (ophthalmologic, cardiologic, among others) to rule out the existence of associated anomalies, which are more frequent than previously considered.

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An infant with Dandy-Walker malformation and prenatally diagnosed tetrasomy 9p is reported. Chromosomal analysis of primary amniocyte culture revealed true mosaicism for two cell lines: 50% of the cells had an isochromosome 9p (pter-q13::q13-pter), and the other 50% showed a normal female karyotype (46,XX). After birth the same chromosomal abnormality was found in 75% of peripheral blood lymphocytes. Phenotypic features included intrauterine growth retardation, hypotrophy of the left side of the body with left microphthalmus, and progressive hydrocephalus secondary to Dandy-Walker malformation. Although most cases of Dandy-Walker malformation are not associated with chromosomal abnormalities, our case, together with two previously reported cases of the same association, indicates that this chromosomal disorder should be looked for in children with Dandy-Walker malformation and abnormal somatic development.

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