Fine-mapping of 5q12.1-13.3 unveils new genetic contributors to caries

Caries is a multifactorial disease and little is still known about the host genetic factors influencing susceptibility. Our previous genome-wide linkage scan has identified the interval 5q12.1-5q13.3 as linked to low caries susceptibility in Filipino families. Here we fine-mapped this region in order to identify genetic contributors to caries susceptibility. Four hundred and seventy-seven subjects from 72 pedigrees with similar cultural and behavioral habits and limited access to dental care living in the Philippines were studied. DMFT scores and genotype data of 75 single-nucleotide polymorphisms were evaluated in the Filipino families with the Family-Based Association Test. For replication purposes, a total 1,467 independent subjects from five different populations were analyzed in a case-control format. In the Filipino cohort, statistically significant and borderline associations were found between low caries experience and four genes spanning 13 million base pairs (PART1, ZSWIM6, CCNB1, and BTF3). We were able to replicate these results in some of the populations studied. We detected PART1 and BTF3 expression in whole saliva, and the expression of BTF3 was associated with caries experience. Our results suggest BTF3 may have a functional role in protecting against caries.

Association of AXIN2 with non-syndromic oral clefts in multiple populations

We have previously shown the association of AXIN2 with oral clefts in a US population. Here, we expanded our study to explore the association of 11 AXIN2 markers in 682 cleft families from multiple populations. Alleles for each AXIN2 marker were tested for transmission distortion with clefts by means of the Family-based Association Test. We observed an association with SNP rs7224837 and all clefts in the combined populations (p = 0.001), and with SNP rs3923086 and cleft lip and palate in Asian populations (p = 0.004). We confirmed our association findings in an additional 528 cleft families from the United States (p < 0.009). We tested for gene-gene interaction between AXIN2 and additional cleft susceptibility loci. We assessed and detected Axin2 mRNA and protein expression during murine palatogenesis. In addition, we also observed co-localization of Axin2 with Irf6 proteins, particularly in the epithelium. Our results continue to support a role for AXIN2 in the etiology of human clefting. Additional studies should be performed to improve our understanding of the biological mechanisms linking AXIN2 to oral clefts.

Novel cleft susceptibility genes in chromosome 6q

Cleft lip/palate is a defect of craniofacial development. In previous reports, chromosome 6q has been suggested as a candidate region for cleft lip/palate. A multipoint posterior probability of linkage analysis of multiplex families from the Philippines attributed an 88% probability of harboring a cleft-susceptibility gene to a narrower region on bands 6q14.2-14.3. We genotyped 2732 individuals from families and unrelated individuals with and without clefts to investigate the existence of possible cleft-susceptibility genes in this region. We found association of PRSS35 and SNAP91 genes with cleft lip/palate in the case-control cohort and in Caucasian families. Haplotype analyses support the individual associations with PRSS35. We found Prss35 expression in the head and palate of mouse embryos at critical stages for palatogenesis, whereas Snap91 was expressed in the adult brain. We provide further evidence of the involvement of chromosome 6q in cleft lip/palate and suggest PRSS35 as a novel candidate gene.

Genetic evidence for the role of loci at 19q13 in cleft lip and palate

BACKGROUND

Clefts of the lip and palate are common birth defects, affecting approximately 1 in 700 births worldwide. The aetiology of clefting is complex, with multiple genetic and environmental influences.

METHODS

Genotype based linkage disequilibrium analysis was conducted using the family based association test (FBAT) and the likelihood ratio test (LRT). We also carried out direct sequencing of the PVR and PVRL2 candidate genes based on their homology to PVRL1, a gene shown previously to cause Margarita Island clefting. Participants included 434 patients with cleft lip with or without cleft palate or cleft palate only and their mothers from eight countries in South America, 205 nuclear triads (father-mother-affected child) from Iowa, 541 nuclear triads from Denmark, and 100 patients with cleft lip and palate from the Philippines.

RESULTS

An allelic variant in the PVR gene showed statistically significant association with both South American and Iowa populations (p = 0.0007 and p = 0.0009, respectively). Direct sequencing of PVR and PVRL2 yielded 26 variants, including two rare amino acid changes, one in each gene, which were not seen in controls.

CONCLUSIONS

We found an association between a common variant in a gene at 19q and isolated clefting in two heterogeneous populations. However, it is unclear from our data if rare variants in PVR and PVRL2 are sufficient to cause clefting in isolation.

Complete sequencing shows a role for MSX1 in non-syndromic cleft lip and palate

MSX1 has been proposed as a gene in which mutations may contribute to non-syndromic forms of cleft lip and/or cleft palate. Support for this comes from human linkage and linkage disequilibrium studies, chromosomal deletions resulting in haploinsufficiency, a large family with a stop codon mutation that includes clefting as a phenotype, and the Msx1 phenotype in a knockout mouse. This report describes a population based scan for mutations encompassing the sense and antisense transcribed sequence of MSX1 (two exons, one intron). We compare the completed genomic sequence of MSX1 to the mouse Msx1 sequence to identify non-coding homology regions, and sequence highly conserved elements. The samples studied were drawn from a panethnic collection including people of European, Asian, and native South American ancestry. The gene was sequenced in 917 people and potentially aetiological mutations were identified in 16. These included missense mutations in conserved amino acids and point mutations in conserved regions not identified in any of 500 controls sequenced. Five different missense mutations in seven unrelated subjects with clefting are described. Evolutionary sequence comparisons of all known Msx1 orthologues placed the amino acid substitutions in context. Four rare mutations were found in non-coding regions that are highly conserved and disrupt probable regulatory regions. In addition, a panel of 18 population specific polymorphic variants were identified that will be useful in future haplotype analyses of MSX1. MSX1 mutations are found in 2% of cases of clefting and should be considered for genetic counselling implications, particularly in those families in which autosomal dominant inheritance patterns or dental anomalies appear to be cosegregating with the clefting phenotype.

Inheritance of cleft palate in South America: evidence for a major locus recessive

OBJECTIVES

Determine the model of inheritance of non-syndromic cleft palate in humans.

DESIGN

Complex segregation analysis performed in families of consecutive newborns affected with non-syndromic cleft palate.

SETTING AND SAMPLE POPULATION

The Latin American Collaborative Study of Congenital Malformations (ECLAMC). Four hundred and seven consecutive newborns affected with non-syndromic cleft palate registered during the period 1967-97.

OUTCOME MEASURE

Likelihood ratio test and Akaike information criterion (AIC) values.

RESULTS

The single major locus recessive model provided a significantly better explanation of the data. It was the most parsimonious and had the smallest AIC value of the six models tested with approximately the same likelihood as the general model (chi2 = 2.44, p = 0.5).

CONCLUSIONS

To have defined a genetic model for non-syndromic cleft palate and provided evidence for a single major locus inheritance suggests that genetic linkage studies could be implemented.

MSX1 and TGFB3 contribute to clefting in South America

MSX1 and TGFB3 have been proposed as genes in which mutations may contribute to non-syndromic forms of oral clefts; however, an interaction between these genes has not been described. The present study attempts to detect transmission distortion of MSX1 and TGFB3 in 217 South American children from their respective mothers. With transmission disequilibrium test analysis, cleft lip with/without cleft palate, cleft lip with palate plus cleft palate only, and all datasets combined showed evidence of association with MSX1 (p = 0.004, p = 0.037, and p = 0.001, respectively). With likelihood ratio test analysis, "cleft lip only" showed association with MSX1 (p = 0.04) and "cleft palate only" with TGFB3 (p = 0.02). A joint analysis of MSX1 and TGFB3 suggested that there may be an interaction between these two loci to increase cleft susceptibility. These results suggest that MSX1 and TGFB3 mutations make a contribution to clefts in South American populations.

Genetic origins in a South American clefting population

It has been proposed that susceptibility to clefting in South America is related to Amerindian ancestry, where clefting is present at a higher frequency than in the other admixed populations (Caucasian and African) that make up the diverse racial mix of current South Americans. To clarify the genetic origins and establish a method for genetic mapping, mitochondrial DNA variation and Y-chromosome markers were studied in a South American population affected with clefting. Two-hundred and seventeen subjects and matched controls were selected through the Latin-American Collaborative Study of Congenital Malformations (ECLAMC). The case group showed a higher frequency of Native American haplogroups and a lower frequency of African haplogroups (p < 0.00001). In addition, the case group showed a much higher frequency of the specific native American haplogroup D than the control group (p < 0.00001). For the Y-chromosome markers, the case group showed a lower frequency of the African-specific marker, YAP (p = 0.002), and a higher frequency of the Native American-specific marker, DYS199 (p < 0.00001). Even though differences were found in the frequencies of the markers studied, the contribution of each founder population was similar for both groups. Results suggest a strong Native American maternal contribution and a strong Caucasian (Spanish and Portuguese) paternal contribution to the population studied. The implications of this finding include the possibility of using admixture mapping approaches to this population.

Candidate genes for nonsyndromic cleft lip and palate

The confirmation of supposed genes causing susceptibility to nonsyndromic cleft lip with or without a cleft palate (CL/P) and cleft palate alone (CP) would help to understand the molecular development of the lip, the palate and the jaw, and to predict more accurately the risk of recurrence of such defects. The purpose of this article is to present a brief review of the current state of knowledge regarding the search for genes responsible for the occurrence of CL/P and CP. After ten years of research, approximately twenty candidate genes have already been suggested for CL/P and CP. Some genes or chromosomal regions seem to be frequently associated with these defects and a specific nomenclature (orofacial cleft genes--OFC) has been suggested. Everything indicates that it will still take many years of research before the genes responsible for CL/P and CP are confirmed. These efforts are justified, however, because of the possibility of being able to predict more accurately the risk of such defects occurring.

Identification of novel mutations in SHH and ZIC2 in a South American (ECLAMC) population with holoprosencephaly

Holoprosencephaly (HPE) is genetically heterogeneous with four genes, SIX3, SHH, TGIF, and ZIC2 that have been identified to date and that are altered in 12% of patients. To analyze this prevalence in a South American population-based sample (57 HPE cases in 244,511 live and still births or 1 in 4300), we performed a mutational study of these genes in 30 unrelated children (26 newborns and 4 non-newborns) with HPE being ascertained by ECLAMC (Latin American Collaborative Study of Congenital Malformations). We identified three novel mutations: two were missense mutations of the SHH gene (Cys183-->Phe; His140-->Pro); the third mutation was a 2-bp deletion in the zinc-finger region of the ZIC2 gene. These molecular results explained 8% (2/26 newborn samples) of the HPE cases in this South American population-based sample, a proportion similar to our previously published data from a collection of cases.

Correlation between molecular and conventional genealogies in Aicuña: a rural population from Northwestern Argentina

Aicuña is a village in the northwest of Argentina, located about 300 km south of La Rioja city, in the province of La Rioja. The population of Aicuña derives from a founder couple established in the uninhabited Aicuña valley in the early years of the 17th century. Due to land ownership litigation, the descendants maintained a well-documented genealogy that extends for 12 generations, comprising more than 8,000 individuals. From the historical pedigree of Aicuña, we selected 14 males with direct patrilineal descent from the 2 most ancient male founders, and 23 donors (9 females and 14 males) with direct matrilineal descent from the most ancient female founder. All 3 founders lived in the 17th century. We collected DNA from buccal swabs and characterized the mitochondrial DNA (mtDNA) and Y haplotypes using 14 Y-specific markers, 11 mtDNA polymorphic markers and sequencing of the mt hypervariable regions 1 and 2. We found four different Y haplotypes: Y1 and Y2 haplotypes of European origin corresponding to the founder ancestors Francisco Páez de Espinoza and Apolinario Ormeño, which were shared by 6 and 3 donors, respectively. Three males selected as Ormeño patrilineal descendants showed a different Y haplotype (Y3), probably originated by erroneous paternity registration due to illegitimacy. The remaining case (haplotype Y4), also assumed to belong to the Ormeño lineage, was probably also due to an erroneously registered paternity. Twenty-two donors showed an association of mtDNA markers corresponding to the Amerindian haplotype A2. The founder of this matrilineage could be traced back for more than 14 generations. The haplotype B of one remaining female did not correspond with the historical pedigree and could be due to an error in the genealogy registration. Our results showed an 85% agreement between conventional and molecular genealogies, with mtDNA markers being Amerindian, and Y markers being European. The methodology used in this report is a tool which could potentially be employed as a precedent for land ownership by Aicuña villagers and Amerindian populations.

Isolated small intestinal atresias in Latin America and Spain: epidemiological analysis

Stenosis, atresia, or absence of part of the duodenum, jejunum, or ileum are generally considered small intestinal atresias (SIAs). SIAs occur as isolated defects, in combination with other unrelated congenital anomalies, or as part of syndromes. We performed an epidemiological study of infants with isolated SIAs using data from two large congenital defects registries, one from Latin America (ECLAMC) and the other from Spain (ECEMC). The overall prevalence of SIAs is similar in both programs, being 1.32 per 10,000 livebirths in Spain and 1.29 per 10.000 livebirths in Latin America. Our results suggest that infants with isolated SIAs are characterized epidemiologically on the basis of shorter gestational age and low birthweight, an association with twinning, the parents are more frequently consanguineous, and their pregnancies are more frequently complicated by vaginal bleeding. The results also suggest an association between some maternal infections and ileal atresia. The fact that these characteristics have been observed in children with these types of anomalies occurring in different geographical areas and populations supports the conclusion that these characteristics are causally related to these defects.

Epidemiological assessment of misoprostol teratogenicity

OBJECTIVE

To verify if any of the 15 congenital defects already reported in association with misoprostol can be found within an epidemiological registry of congenital defects.

DESIGN

Case-control study including case-sick and case-health controls.

METHODS

Comparison of misoprostol exposure for each specific defect, using the exposure for the rest of defects as a reference group.

POPULATION

Four thousand six hundred seventy-three consecutive newborn infants with malformations of unknown aetiology, in the Latin American Collaborative Study of Congenital Malformation.

RESULTS

There was no difference in exposure rate between the malformed (34/4,673) and nonmalformed (23/4,980) newborns. Four of the five more frequently cited defects in the literature were found to be in excess: constriction ring, terminal transverse-limb defects, hydrocephalus, and arthrogryposis. Equinovarus feet had a normal frequency in our study. Thirteen different defects not described in the literature were seen in our misoprostol exposed cases, but only holoprosencephaly and bladder exstrophy significantly exceeded the expected number.

CONCLUSIONS

The confirmation from an epidemiological registry of an association for four of the five more commonly observed congenital defects among misoprostol exposed children described in the literature seems indicative of a real teratogenic effect. The defects are of vascular disruption type. However, additional attempts to achieve abortion could not be excluded as a concurrent contribution.

Pregnancy outcome after exposure to misoprostol in Brazil: a prospective, controlled study

BACKGROUND

Misoprostol, a synthetic prostaglandin E1 analog is labeled for the treatment of gastric and duodenal ulcers. In Brazil, where abortion is not a legal procedure, there is a widespread popular misuse of this drug in abortion attempts. This misuse and the fact that, in many cases the desired pregnancy termination does not occur, raise concerns about fetal safety. Case reports of congenital anomalies after maternal use of misoprostol have been published. The objective of this work was to compare pregnancy outcome following misoprostol exposure with a matched control group. This is the first prospective controlled study on fetal safety after misoprostol use.

METHODS

A prospective, observational cohort study with 86 exposed and 86 pair-matched, non-exposed controls.

RESULTS

There was no significant difference in the rates of major or minor birth between exposed compared to non-exposed infants (2/67 vs 2/81, major defects; 7/67 vs. 3/81, minor anomalies) There were significantly more miscarriages in the exposed group (17.1% vs. 5.8%; relative risk, 2.97; 95% confidence interval, 1.12 to 7.88). There was no statistical difference in gestational age at delivery, birth weight, sex ratio, rate of prematurity, low birth weight, or rates of cesarean section between groups.

CONCLUSIONS

Our study, despite its limited statistical power, does not suggest a potent teratogenic action of misoprostol exposure during pregnancy.

Thumb/hallux duplication and preaxial polydactyly type I

It was recently shown that hand postaxial polydactyly differed from foot postaxial polydactyly. The aim of this work was to test whether thumb and hallux duplication also had different clinical and epidemiological characteristics, depending on limb involvement. We studied 920 newborn infants with first digit duplication, ascertained among 3,444,374 births by the Latin-American Collaborative Study of Congenital Malformations (ECLAMC), from 1967 to 1995. Since biphalangeal thumb duplication or hallux duplication can occur in families with triphalangeal thumb or polysyndactylous propositi, these groups were also analyzed. The 715 isolated (nonsyndromal) cases (prevalence 2.08 per 10,000) were subdivided into five groups: thumb duplication (N = 568; prevalence: 1.65/10,000); hallux duplication (N = 82; prevalence: 0.24); thumb and/or hallux duplication plus syndactyly (polysyndactyly) (N = 37; prevalence: 0.11); triphalangeal thumb (N = 24; prevalence: 0.07), and thumb duplication plus hallux duplication (N = 4; prevalence: 0.01). Both thumb and hallux duplication groups showed a significant excess of males, and right sidedness was also more frequent in both of them, though without statistical significance for hallux duplication. Thumb duplication was more often unilateral (94.7% versus hallux duplication of 81.5%), and its prevalence was higher in Bolivia (3.37/10,000) than in the other 10 Latin-American countries included (1.62/10,000). In a subseries of 405 preaxial polydactylies with matched controls, a logistic regression analysis showed that birth weight and gestational age had an effect on the calculated risk of having an infant with thumb duplication, while first trimester vaginal bleeding had only a borderline effect. None of the polydactyly groups showed abnormal values for twinning, perinatal mortality, ethnicity, maternal education, parental ages, parity, parental subfertility, or consanguinity. There were 70/405 familial cases. Their pedigrees were compatible with autosomal dominant inheritance with a 9% penetrance for thumb duplication and hallux duplication and a 70% penetrance for triphalangeal thumb and polysyndactyly. Inheritance of thumb duplication and probably the untested inheritance of hallux duplication were also compatible with a four-locus multiplicative model. The observed differences in laterality, geographical distribution, birth weight, gestational age, and first trimester vaginal bleeding between thumb duplication and hallux duplication groups suggested that apparent preaxial polydactyly type 1 is a causally heterogeneous group.

Survival of children with Down syndrome in South America. ECLAMC-Downsurv Group. Latin American Collaborative Study of Congenital Malformations

The first step of all healthcare actions aimed at promoting an appropriate quality of life for infants affected by Down syndrome (DS) is to ensure their survival. This investigation was aimed at estimating the infant mortality rate of infants affected with DS in urban populations of South America. Thirty-three hospitals included in the Latin American Collaborative Study of Congenital Malformations (ECLAMC) distributed in 23 cities of 5 South American countries followed 360 liveborn DS cases born during the 1988-1992 period. Families were recontacted after the infant should have reached the age of one year. The collected data included information about health status; i.e., frequency and dates of diagnosed illnesses and hospital admissions, and, in case of death, information on date, place and cause of death, and illness immediately before death. Information about the interviews included place, date, and name of the interviewer. A closed questionnaire was employed by the interviewers, mostly physicians, nurses, and social workers. Life table analysis up to the age of one year was performed by the actuarial survival method. The overall mean survival at age one year was 0.736 (SE=0.023). Thirty-three (9.2%) of the 360 cases died neonatally, and 62 (17.2%) within the remaining 2-to-12-month interval. The probability of survival at one year of age did not differ between public (209 cases; mean 0.718; SE=0.031) and private (151 cases; mean: 0.762; SE=0.035) (chi2:0.87; df:1; P >0.05) health systems. The 150 DS cases with a congenital heart defect (CHD) had a significantly lower P robability of survival at the age of one year (mean: 0.660; SE: 0.039) than did the 210 cases without CHD (mean: 0.790; SE: 0.028) (chi2:6.67; df:1; P <0.01). The death rate in the first year of life for DS cases without a detected cardiac defect (21%) is significantly higher than that reported in developed countries; namely, 16% from Italy, 11% from Canada, 10% from England, and 7% from Denmark.

Thalidomide, a current teratogen in South America

Thalidomide, mainly used for the treatment of leprosy, is a current teratogen in South America, and it is reasonable to assume that at present this situation is affecting many births in underdeveloped countries. Moreover, the potential re-marketing of thalidomide for the treatment of a large variety of diseases may extend the problem to the developed world. When the drug is available, the control of its intake during early pregnancy is very difficult since most pregnancies are unintended. The ongoing occurrence of thalidomide embryopathy cases went undetected by the ECLAMC, due to several factors: (1) low populational coverage through this monitoring system; (2) pre-existence of the teratogen with its effects present in both baseline (expected) and monitored (observed) materials; and (3) lack of a defined phenotype to be monitored. Thus, if thalidomide re-enters the market throughout the world, due to the wide range of new applications, occurrence of phocomelia alone might not be sufficient to detect its effects. By a case-reference approach, the ECLAMC registered 34 thalidomide embryopathy cases born in South America after 1965 whose birthplaces correspond to endemic areas for leprosy. Phocomelia was found in five of eleven fully described cases. Thus, phocomelia alone is neither specific nor sufficient to serve as a suitable phenotype to survey the teratogenic effects of thalidomide. Therefore, a thalidomide-like phenotype, defined as any bilateral upper and/or lower limb reduction defect of the preaxial and/or phocomelia types, should be included in the routine surveillance of birth defects in all programmes.

Heterogeneous rates for birth defects in Latin America: hints on causality

The aim of this work was to disclose risk factors associated with birth defects which were heterogeneously distributed in the different geographic regions sampled by the Latin American Collaborative Study of Congenital Malformations (ECLAMC). The material included 2,159,065 hospital births, delivered in the 1967-1989 period in 24 geographic regions of Latin America. Birth defect types with 50 case-control pairs or more were analyzed. A risk factor was defined as that available variable with differential geographic rates, correlated with those of a given birth defect type. Identified factors were tested by case-control multivariate logistic regression to confirm their role in the occurrence of the defect. Altitude and maternal acute illness during first trimester of pregnancy, named influenza, were risk factors for microtia. Prenatal drug exposure, mainly sex hormones, were connected with the occurrence of hypospadias in low frequency areas, while Native ancestry was a "protective" factor in the same regions. Acute (influenza), and chronic (epilepsy and syphilis) maternal illness during first trimester of pregnancy and gravidity higher than four were risk factors for cleft lip. The independence of these variables from maternal age suggested that low maternal socioeconomic level could explain the high birth defect order and, perhaps, syphilis in mothers. Postaxial polydactyly was associated with parental consanguinity, as well as Afro-American ancestry, suggesting genetic heterogeneity.

Achondrogenesis type II with polydactyly

We report on a newborn male infant who presented the typical findings of achondrogenesis type II (Langer-Saldino), and who also showed postaxial polydactyly on both feet and bilateral microtia. Polydactyly is frequently part of the short-rib syndromes, but has not been reported in achondrogenesis. The hypothesis of polydactyly as part of a contiguous gene syndrome is discussed.

Effect of paternal age in achondroplasia, thanatophoric dysplasia, and osteogenesis imperfecta

The paternal ages of nonfamilial cases of achondroplasia (AC) (n = 78), thanatophoric dysplasia (TD) (n = 64), and osteogenesis imperfecta (OI) (n = 106), were compared with those of matched controls, from an Italian Indagine Policentrica Italiana sulle Malformazioni Congenite and a South American Estudio Colaborativo Latinoamericano de Malformaciones Congénitas series. The degree of paternal age effect on the origin of these dominant mutations differed among the three conditions. Mean paternal age was highly elevated in AC, 36.30 +/- 6.74 years in the IPIMC, and 37.19 +/- 10.53 years in the ECLAMC; less consistently elevated in TD, 33.60 +/- 7.08 years in the IPIMC, and 36.41 +/- 9.38 years in the ECLAMC; and only slightly elevated in OI in the ECLAMC, 31.15 +/- 9.25 years, but not in the IPIMC, 32.26 +/- 6.07 years. Increased maternal age or birth order in these conditions disappeared when corrected for paternal age. Approximately 50% of AC and TD cases, and only 30% of OI cases, were born to fathers above age 35 years. For AC and TD, the increase in relative incidence with paternal age fitted an exponential curve. The variability of paternal age effect in these new mutations could be due, among other reasons, to the high proportion of germ-line mosaicism in OI parents, or to the localization of the AC gene, mapped to the 4p16.3 region, in the neighborhood of an unstable DNA area.

Segregation distortion in the offspring of Afro-American fathers with postaxial polydactyly

The unclear pattern of inheritance of postaxial polydactyly prompted this search for evidence of imprinting or change of expression in males and females using material of the Latin American Collaborative Study of Congenital Malformations. The frequency of affected offspring for 196 fathers with polydactyly was compared with that for 233 mothers with the same condition, stratified according to African and non-African ancestry. The postaxial polydactyly prevalence rate among the offspring of affected black fathers (44%) was larger than that in the group of affected black mothers (31%), with no difference between affected nonblack fathers (34%) and affected nonblack mothers (33%). The sex ratio (.51) observed in 631 black propositi and in 829 nonblack propositi with polydactyly (.58) could be a further indication of etiologic heterogeneity for polydactyly between these two ethnic groups. The segregation distortion in favor of affected among the offspring of affected black fathers could be interpreted as the effect of a sex-linked recessive modifier gene acting during gametogenesis on an autosomal dominant polydactyly gene, this modifier being more frequent in Africans.

Monthly and seasonal variations in the frequency of congenital anomalies

Three large and comparable series of births were used to test the working hypothesis that if there is a real seasonal variation in the frequency of a given congenital malformation; it would have to be shown by adequate analysis; to be more overt in non-tropical areas; and to be six months out of phase in northern and southern hemispheres. The data set were hospital births from tropical (287,165 births) and non-tropical (582,585 births) South America, and from Italy (508,536 births). Sixteen well-defined malformation types were tested: anencephaly, spina bifida, cephalocoele, hydrocephaly, microtia, cleft palate, cleft lip, oesophageal atresia, anal atresia, hypospadias, pes equino-varus, pes talovalgus, postaxial polydactylyl, pre-axial polydactylyl, diaphragmatic hernia, and Down's syndrome. No seasonal variation was proven (p less than 0.01) for any malformation type in any of the three series of data by means of Walter and Elwood's test, or Hewitt et al's non-parametric test2 applied to seven instances with sample sizes smaller than 50 cases. Variations of borderline significance (p less than 0.05) included oesophageal atresia in tropical South America, none in non-tropical South America, and anencephaly in Italy. It is concluded that seasonal variation in the occurrence of congenital malformations is a rare phenomenon when tests are strictly used within their recommended limitations.

The epidemiology of conjoined twins in Latin America

Twenty-three cases of symmetrical conjoined twins were registered by the Latin-American Collaborative Study of Congenital Malformations (ECLAMC) in 1,714,952 births, which were observed during the 1967-1986 period in 95 maternity hospitals distributed in eleven Latin-American countries. This results in a birth prevalence rate of about 1/75,000 births. The secular and geographic distribution of this material do not depart from random in spite of one hospital with three cases, and two hospitals with two cases each, within a short time period. These 23 cases include one diprosopus, 3 dicephalus, one ischiopagus, 5 pygopagus, none dipygus, 3 syncephalus, none craniopagus, 9 thoracopagus, one omphalopagus, and one rachipagus. Sex distribution is even, with 12 male and 11 female cases.

Epidemiology of ambiguous genitalia in South America

We present descriptive epidemiologic data on ambiguous genitalia (AG), obtained in the period 1967-1982 by the Latin American Collaborative Study of Congenital Malformations (ECLAMC) through 70 participating hospitals located in 34 cities of 9 South American countries. The observed prevalence rate for isolated AG was about 1/20,000 births, with at least 1/4 and probably as much as 1/2 due to congenital adrenal hyperplasia. When AG cases associated with other congenital anomalies were also considered, the overall frequency of AG was 1/6,900 total births (1/10,000 for live and 1/350 for stillbirths). The prevalence rates were homogeneously distributed among the different countries, and there was a stable secular trend. AG was more frequent in nontropical than in tropical areas of South America, and there was a significant seasonal variation with its acrophase in August (winter). A case-control analysis of 14 risk factors showed an association of AG with a prenatal history of acute maternal illnesses. These data do not support an etiological relationship between AG and hypospadias.

Prevalence rates of microtia in South America

A high frequency of microtia in Quito (Ecuador) was detected by the Latin American Collaborative Study of Congenital Malformations (ECLAMC), and the data available on file were used to define the cluster and to test some potential risk factors. The Quito material consisted of 46 041 livebirths from two hospitals. The rest of the sample consisted of 553 068 livebirths from 58 hospitals located in 24 cities of six other South American countries. The observed prevalence rate for microtia was over five times higher in Quito (17.4/10 000) than in the other cities (3.2/10 000). The microtias from Quito were mostly represented by isolated forms (without other anomalies except for preauricular tags and/or sinuses), and the proportion of severe microtia was higher than in the rest of the sample. Neither seasonal, nor secular variations were observed in Quito or the rest of the sample; data suggesting the geographical cluster did not arise in recent years. Case-control analysis of familial, prenatal and perinatal history data in 184 cases with isolated microtia (68 from Quito and 116 from the rest) and in 184 matched non-malformed control newborn babies, identified prenatal drug exposure, high birth order, and elevated paternal age as risk factors for the microtias born in Quito.

The birth prevalence rates for the skeletal dysplasias

This study was undertaken to establish the prevalence rates at birth of the skeletal dysplasias that can be recognised in the perinatal period. Using the data base of the Latin-American Collaborative Study of Congenital Malformations (ECLAMC), for the years 1978 to 1983, on 349 470 births (live and stillbirths), a crude prevalence rate of 2.3/10 000 was observed. However, several indications of under-registration suggest that the real value is about twice that observed. The most frequent types of skeletal dysplasia were achondroplasia, with a prevalence rate between 0.5 and 1.5/10 000 births, the thanatophoric dysplasia/achondrogenesis group (0.2 and 0.5/10 000 births), and osteogenesis imperfecta (0.4/10 000 births). The mutation rate for autosomal dominant achondroplasia was estimated at between 1.72 and 5.57 X 10(-5) per gamete per generation.

Epidemiology of neural tube defects in South America

We present data from the Latin American Collaborative Study of Congenital Malformations (ECLAMC) on prevalence rates and etiologic factor associations in neural tube defects. Two series of data are analyzed: the A series, including 740,139 consecutive infants born in the 1967-1979 period suitable for secular trend analysis and case-control study of risk factors; and the B series, including 255,834 consecutive stillborn and liveborn infants of the 1980-1982 period suitable for prevalence rate analysis. Anencephaly was registered in 6.0/10,000 births, A spina bifida aperta in 6.2/10,000 births, and cephalocele in 2.4/10,000 births. A stable secular trend was observed for the frequency of all three neural tube defect types. Spina bifida was more frequent in Chile than in the rest of South America. No differences in prevalence rates were seen between tropical and non tropical areas. Parental consanguinity and environmental prenatal factors including maternal illnesses, drug intake, and radiation exposure were found in association with anencephaly and spina bifida.

On monitoring the multiply malformed infant. I: Case-finding, case-recording, and data handling in a Latin American program

The methods used by the Latin American Collaborative Study of Congenital Malformations (ECLAMC) for monitoring the birth prevalence of multiply malformed infants are based on a clinical-epidemiological approach oriented to the early detection of teratogenic agents. They consist of three steps: 1) the analysis of observed vs expected rates of all congenital anomalies (CA), including their isolated and associated forms; 2) the same type of analysis applied to each multiple congenital anomaly (MCA) pattern; and 3) a clinical case presentation reserved only for those considered as true MCA because of presence of three or more independent CA. During the period 1982-1983 299,231 infants were examined. Multiply malformed infants, excluding Down syndrome cases, were born at a rate of 4/10,000, 40% having syndromes (two or more interrelated CA), 30% anomaly pairs, ie, two independent CA, and 30% true MCA cases. In a program with 150,000 births per year, as in ECLAMC, this means about five true MCA cases per week, a number easily handled individually on a clinical basis.

Inbreeding in a South-American newborn series

Parental consanguinity was investigated in a series of 16, 137 non-malformed newborn infants, ascertained in 64 hospitals, of 27 cities, in seven South-American countries. Parental consanguinity was detected in 135 (0.84%) newborns, giving a mean inbreeding coefficient (a) of 0.00053. The subsamples for five of the seven countries (Brazil, Chile, Ecuador, Uruguay, Venezuela) showed similar consanguinity rates, of about one per cent, an a ranging from 0.00040 to 0.00070, approximately. One country, Argentina, had a three times lower value for both indicators: consanguinity rate: 0.3%, a: 0.00011. Another country, Peru, could not be individually analyzed because of its small sample size. Considering the whole South-American sample, first cousin represented 60% of all consanguineous matings. Significantly more female than male intermediate ancestors were counted in the specified total of consanguineous matings, suggesting a preferential consanguineous mating pattern for urban South-American populations.

Pectoralis major muscle defect and Poland complex

Pectoralis major muscle defect (PMD) was diagnosed in 27 infants from a series of 599,109 live births in South America (1/22,189). In all 27 cases the PMD was unilateral, mainly affecting the right side (20/27), and there were more male (19/27) than female cases. No familial cases and no parental consanguinity were recorded. A positive correlation was observed between PMD and sex hormone intake and vaginal bleeding in the first trimester of pregnancy. In 12 (1/49,925) of the 27 PMD cases hypoplasia and/or syndactyly of the ipsilateral hand was also diagnosed. The index-middle interdigital space was affected in all 11 cases with symbrachydactyly. Additional congenital anomalies were observed in 4/27 cases, and they were: hemangiomas, hypospadias, and clubfeet. Poland complex (12 cases), isolated PMD (15 cases), and isolated symbrachydactyly (18 cases), showed a similar pattern for symmetry, sidedness, syndactyly type, and sex ratio.