The incidence of congenital malformations in a Chinese population: the Taipei collaborative study

An Epidemiologic Study of Isolated Cleft Lip, Palate, or Both in Victoria, Australia from 1983 to 2000

Objective

To report the epidemiological characteristics of isolated cleft lip, cleft palate or both (CL ± P and CP) using population-based data in Victoria, Australia.

Design

Descriptive study of a cohort of children born between 1983 and 2000 notified to the Victorian Birth Defects Register by multiple ascertainment sources.

Participants

Data were collected on patients identified with CL ± P and CP without associated defects classified as live births, stillbirths, neonatal deaths, and terminated pregnancies < 20 weeks’ gestation following prenatal identification. Information was collected on sex, plurality, maternal age, and country of birth.

Results

The overall prevalence (per 10,000 pregnancies) of CL ± P was 7.8 (95% confidence interval [CI] = 7.30, 8.33; cleft lip [CL] 3.3; 95% CI = 2.97, 3.65, CL+P 4.5; 95% CI = 4.13, 4.91) and cleft palate (CP), 4.3 (95% CI = 3.89, 4.66). The prevalence of CL + P was higher among stillbirths, neonatal deaths, and terminated pregnancies than CL (without CP) and CP. Boys were at greater risk than girls for CL ± P and girls at greater risk than boys for CP. Regardless of cleft type, there was a nonsignificant excess of clefts among singleton births than multiple births and no related effects of maternal age or country of birth.

Conclusions

The prevalence of isolated CL ± P and CP in Victoria parallels other population-based studies of the same conditions. Inclusion of stillbirths, neonatal deaths, and terminations had little impact on rates. The effect of sex and plurality on cleft type is consistent with the literature, but the effects of maternal age and country of birth remain equivocal. Further studies focusing on certain ethnic groups are warranted to explain the higher rates observed.

Asian Oral-Facial Cleft Birth Prevalence

Objective:

To determine the clefting birth prevalence among Asian populations, specifically Chinese and Japanese, using raw counts from nonoverlapping published studies of Asian populations, and to investigate whether Asian clefting rates have been interpreted accurately as being up to twice the Caucasian rate.

Design:

A literature review of articles giving raw counts of clefting in Asian populations, primarily Japanese and Chinese.

Main Outcome Measures:

Where possible, clefts were identified by the patients’ ethnicity, country of origin, cleft type, syndromic status, and birth status.

Results:

Prevalence rates of cleft lip with or without cleft palate per 1000 live births are reported. Syndromic plus nonsyndromic cleft lip with or without cleft palate: Chinese, 1.30; Japanese, 1.34; Other Asian, 1.47; and total, 1.33. Nonsyndromic cleft lip with or without cleft palate: Chinese, 1.20; Japanese, 1.18; Other Asian, 1.22; and total, 1.19.

Conclusions:

Overall, Chinese and Japanese live birth prevalence rates for nonsyndromic cleft lip with or without cleft palate, based on the published reports of birth prevalence, are significantly lower than the oft-quoted rate of 2 per 1000 for Asians. The apparent reason for the discrepancy is that many published prevalence rates included all pregnancies (live births plus pregnancy losses) and do not distinguish between syndromic and nonsyndromic clefts or between cleft palate alone and cleft lip with or without cleft palate. These results demonstrate that it is extremely important for current population-based studies of clefts to include careful delineation of population groups, syndromes, cleft type, and birth status.

Birth prevalence of congenital talipes equinovarus in low- and middle-income countries: a systematic review and meta-analysis

OBJECTIVE

Congenital talipes equinovarus (CTEV), or clubfoot, is a structural malformation that develops early in gestation. Birth prevalence of clubfoot is reported to vary both between and within low- and middle-income countries (LMICs), and this information is needed to plan treatment services. This systematic review aimed to understand the birth prevalence of clubfoot in LMIC settings.

METHODS

Six databases were searched for studies that reported birth prevalence of clubfoot in LMICs. Results were screened and assessed for eligibility using pre-defined criteria. Data on birth prevalence were extracted and weighted pooled estimates were calculated for different regions. Wilcoxon rank-sum test was used to examine changes in birth prevalence over time. Included studies were appraised for their methodological quality, and a narrative synthesis of findings was conducted.

RESULTS

Forty-eight studies provided data from 13 962 989 children in 20 countries over 55 years (1960-2015). The pooled estimate for clubfoot birth prevalence in LMICs within the Africa region is 1.11 (0.96, 1.26); in the Americas 1.74 (1.69, 1.80); in South-East Asia (excluding India) 1.21 (0.73, 1.68); in India 1.19 (0.96, 1.42); in Turkey (Europe region) 2.03 (1.54, 2.53); in Eastern Mediterranean region 1.19 (0.98, 1.40); in West Pacific (excluding China) 0.94 (0.64, 1.24); and in China 0.51 (0.50, 0.53).

CONCLUSION

Birth prevalence of clubfoot varies between 0.51 and 2.03/1000 live births in LMICs. A standardised approach to the study of the epidemiology of clubfoot is required to better understand the variations of clubfoot birth prevalence and identify possible risk factors.

Time trend of incidence rates of cleft lip/palate in Taiwan from 1994 to 2013

Background

This study was to estimate the incidence rate of cleft lip and/or cleft palate (CL/P) in Taiwan from 1994 to 2013, and to assess the time trend over these years.

Methods

Retrospective data analysis was performed on records of all newborns with CL/P treated at Chang Gung Craniofacial Center, the only treatment center for CL/P in Taiwan, from 1994 to 2013. Three-year moving average rates were computed and linear regression was used to explore the annual average percentage change.

Results

From 1994 to 2013, 7282 newborns with CL/P were identified, corresponding to an annual rate of 1.48‰ (95% confidence interval (CI) = 1.45‰–1.52‰). There was a significant decline of rate of cleft lip with or without cleft palate (CL ± P) (−2.9% ± 0.2%, p < 0.0001) but slightly increase of rate of cleft palate (CP) only (+0.2% ± 0.07%, p = 0.004).

Conclusion

From 1994 to 2013, the annual rate of incidence of CL/P was 1.48‰ in Taiwan. The 2.9% annual decline of the rate was mainly from the CL ± P group, not the CP group.

Pattern and factors associated with congenital anomalies among young infants admitted at Bugando medical centre, Mwanza, Tanzania

BACKGROUND

Congenital anomalies or birth defects are among the leading causes of infant mortality and morbidity around the world. The impact of congenital anomalies is particularly severe in middle- and low-income countries where health care resources are limited. The prevalence of congenital anomalies varies in different parts of the world, which could reflect different aetiological factors in different geographical regions.

METHODS

Between October 2012 and January 2013, a cross-sectional study was conducted involving young infants below 2 months of age, admitted at a university teaching hospital in Tanzania. Face-to-face interviews with parents/caretakers of young infants were carried out to collect socio-demographic and clinical information. Physical examinations were performed on all young infants. Echocardiography, X-ray, cranial as well as abdominal ultrasonographies were performed when indicated.

RESULTS

Analysis of the data showed that among 445 young infants enrolled in the study, the prevalence of congenital anomalies was 29%, with the Central Nervous System (CNS) as the most commonly affected organ system. Maternal factors that were significantly associated with congenital anomalies included the lack of peri-conceptional use of folic acid (OR = 3.1; 95% CI = 1.4-6.7; p = 0.005), a maternal age of above 35 years (OR = 2.2; 95% CI = 1.1-4.3; p = 0.024) and an inadequate attendance to antenatal clinic (OR = 2.1; 95% CI = 1.4-3.3; p < 0.001). Infant factors that were significantly associated with congenital anomalies were female sex, a birth weight of 2.5 kg or more, singleton pregnancy and a birth order above 4.

CONCLUSIONS

Due to the high prevalence of congenital anomalies observed in this particular context, the hospital should mobilize additional resources for an optimal and timely management of the patients with congenital anomalies. In this study, the proportion of women taking folic acid supplements during early pregnancy was very low. Efforts should be made to ensure that more women use folic acid during the peri-conceptional period, as the use of folic acid supplement has been linked by several authors to a reduced occurrence of some congenital anomalies.

Conjoined twins: a worldwide collaborative epidemiological study of the International Clearinghouse for Birth Defects Surveillance and Research

Conjoined twins (CT) are a very rare developmental accident of uncertain etiology. Prevalence has been previously estimated to be 1 in 50,000 to 1 in 100,000 births. The process by which monozygotic twins do not fully separate but form CT is not well understood. The purpose of the present study was to analyze diverse epidemiological aspects of CT, including the different variables listed in the Introduction Section of this issue of the Journal. The study was made possible using the International Clearinghouse for Birth Defects Surveillance and Research (ICBDSR) structure. This multicenter worldwide research includes the largest sample of CT ever studied. A total of 383 carefully reviewed sets of CT obtained from 26,138,837 births reported by 21 Clearinghouse Surveillance Programs (SP) were included in the analysis. Total prevalence was 1.47 per 100,000 births (95% CI: 1.32-1.62). Salient findings including an evident variation in prevalence among SPs: a marked variation in the type of pregnancy outcome, a similarity in the proportion of CT types among programs: a significant female predominance in CT: particularly of the thoracopagus type and a significant male predominance in parapagus and parasitic types: significant differences in prevalence by ethnicity and an apparent increasing prevalence trend in South American countries. No genetic, environmental or demographic significant associated factors were identified. Further work in epidemiology and molecular research is necessary to understand the etiology and pathogenesis involved in the development of this fascinating phenomenon of nature.

Ethnic variations in the estimated prevalence of orofacial clefts in Taiwan, 2004 to 2006

BACKGROUND

Foreign-born mothers have been reported to have better pregnancy outcomes as measured by the preterm birth rate, neonatal mortality, and birth weight compared with native-born mothers in Belgium, France, Taiwan, and the United States. However, little is known about the association between maternal nationality and the prevalence of orofacial clefts in Asian countries.

METHODS

Taiwan Birth Registry data from 2004 to 2006 were analyzed for an association between maternal nationality and orofacial clefts. Singleton live births with a gestational age ≥24 weeks were included in this study.

RESULTS

The overall estimated prevalence percentages of orofacial clefts were 0.11 (95% confidence interval [CI]  =  0.03 to 0.12) among newborns of Taiwan-born mothers (TBMs) and 0.13 (95% CI  =  0.04 to 0.16) among newborns of foreign-born mothers (FBMs), respectively. The estimated prevalence of orofacial clefts of all live births of FBMs in Taiwan was similar to that of the FBMs from Southeast Asian countries.

CONCLUSION

There was a slightly higher but no significant difference of estimated prevalence of orofacial clefts between newborns of TBMs and newborns of FBMs in Taiwan.

Prenatal diagnosis, pregnancy terminations and prevalence of Down syndrome in Atlanta

BACKGROUND

The impact of prenatal diagnosis on the live birth prevalence of Down syndrome (trisomy 21) has been described. This study examines the prevalence of Down syndrome before (1990-1993) and after inclusion of prenatally diagnosed cases (1994-1999) in a population-based registry of birth defects in metropolitan Atlanta.

METHODS

We identified infants and spontaneous fetal deaths with Down syndrome (n = 387), and pregnancies electively terminated after a prenatal diagnosis of Down syndrome (n = 139) from 1990 to 1999 among residents of metropolitan Atlanta from a population-based registry of birth defects, the Metropolitan Atlanta Congenital Defects Program (MACDP). Only diagnoses of full trisomy 21 were included. Denominator information on live births was derived from State of Georgia birth certificate data. We compared the prevalence of Down syndrome by calendar period (1990-1993, 1994-1999), maternal age (<35 years, 35+ years), and race/ethnicity (White, Black, other), using chi-square and Fisher's exact tests.

RESULTS

During the period when case ascertainment was based only on hospitals (1990-1993), the prevalence of Down syndrome was 8.4 per 10,000 live births when pregnancy terminations were excluded and 8.8 per 10,000 when terminations were included. When case ascertainment also included perinatal offices (1994-1999), the prevalence of Down syndrome was 10.1 per 10,000 when terminations were excluded and 15.3 when terminations were included. During 1990-1993, the prevalence of Down syndrome was 24.7 per 10,000 among offspring to women 35+ years of age compared to 6.8 per 10,000 among offspring to women <35 years of age (rate ratio [RR] = 3.65, 95% confidence interval [CI] = 2.53-5.28). During 1994-1999, the prevalence of Down syndrome was 55.3 per 10,000 among offspring to women 35+ years compared to 8.5 per 10,000 among offspring to women <35 years (RR = 6.55, 95% CI = 5.36-7.99). There was no statistically significant variation in the prevalence of Down syndrome by race/ethnicity within maternal age and period of birth strata. During 1994-1999, the proportion of cases that were electively terminated was greater for women 35+ years compared to women <35 years (RR = 5.10, 95% CI = 3.14-8.28), and lower for Blacks compared to Whites among women 35+ years of age (RR = 0.33, 95% CI = 0.16-0.66).

CONCLUSIONS

In recent years, perinatal offices have become an important source of cases of Down syndrome for MACDP, contributing at least 34% of cases among pregnancies in women 35+ years of age. Variation in the prevalence of Down syndrome by race/ethnicity, before or after inclusion of cases ascertained from perinatal offices, was not statistically significant. Among Down syndrome pregnancies in mothers 35+ years we found a lower proportion of elective termination among Black women compared to White women. We suggest that future reports on the prevalence of Down syndrome by race/ethnicity take into account possible variations in the frequency of prenatal diagnosis or elective termination by race/ethnicity.

Descriptive epidemiology of nonsyndromic cleft lip with or without cleft palate in Shanghai, China, from 1980 to 1989

OBJECTIVE

The purpose of this study was to characterize nonsyndromic cleft lip with or without cleft palate (CL+/- CP) in an Asian population.

DESIGN

Birth prevalence was assessed in a large birth series in Shanghai, China. A 1:3 sex-age-hospital matched case-control design was used to assess the effects of parental ages and pregnancy history on risk of CL+/- CP.

PARTICIPANTS

Records of live births from 1980 to 1989 in 22 hospitals in Shanghai, China, were reviewed, comprising 541,504 consecutive births, which is by far the largest such Chinese sample ever investigated. The case-control study included 528 (308 male, 220 female) nonsyndromic CL+/- CP cases and 1,563 (912 male, 651 female) controls.

RESULTS

From 1980 to 1989, the overall birth prevalence was 1.2 per 1,000 live births with statistically significant seasonal variation (more CL+/- CP births in January to July). The overall male:female ratio was 1.40:1. For males, statistically significant associations were identified with maternal age for the most severe clefts (bilateral overall, and also bilateral CL+CP subgroup). For females, statistically significant association was shown for pregnancy age with birth order (overall and in most subgroups).

CONCLUSIONS

The birth prevalence of CL+/- CP in this Asian population was similar to published Caucasian rates. The observed seasonal variation would be consistent with possible environmental factors. Significant associations with maternal age, pregnancy age, and birth order warrant additional study of pregnancy history in Asian CL+/- CP.

Racial and ethnic variations in the prevalence of orofacial clefts in California, 1983-1992

To investigate variations in the prevalence of oral cleft anomalies according to parental race and ethnicity and maternal country of birth, the authors analyzed a cohort of 2,221,755 live births and fetal deaths delivered between 1983 and 1992 to residents of California. A total of 2,329 cleft lip with or without cleft palate (CL +/- P) cases and 1,475 cleft palate alone (CP) cases were identified by the California Birth Defects Monitoring Program, a population-based registry. Compared to Whites, the prevalence of CL +/- P was lower among African Americans (prevalence ratio (PR) = 0.56, 95% confidence interval (CI) = 0.45-0.69), higher among Native Americans (PR = 1.81, CI = 1.20-2.69), and the same among the Japanese (PR = 1.07, CI = 0.62-1.82) and Chinese (PR = 0.96, CI = 0.71-1.29). The risk of CL +/- P was slightly lower among the offspring of foreign-born Chinese women relative to U.S.-born Chinese women (PR = 0.71, CI = 0.33-1.57), and slightly higher among foreign-born Filipinos relative to their U.S.-born counterparts (PR = 1.37, CI = 0.57-3.53), although confidence intervals around these risk estimates were wide owing to sparse data. For CP, lower prevalences were observed among African Americans (PR = 0.72, CI = 0.58-0.91) and Hispanics (PR = 0.77, CI = 0.67-0.87) than among Whites. The risk of CP was higher among foreign-born Filipinos compared to U.S.-born Filipinos (PR = 1.52, CI = 0.58-4.33), although the confidence interval around this estimate included unity. These prevalence variations may reflect differences in both environmental and genetic factors affecting clefting risk.

Descriptive epidemiology of holoprosencephaly and arhinencephaly in metropolitan Atlanta, 1968-1992

We report the descriptive epidemiology of holoprosencephaly and arhinencephaly using data from the Metropolitan Atlanta Congenital Defects Program, a population-based birth defects surveillance system with multiple sources of ascertainment. From 1968-1992, we ascertained 63 cases of holoprosencephaly and arhinencephaly from approximately 734,000 births, for a birth prevalence of 0.86 per 10,000. Thirteen case infants with holoprosencephaly and four case infants with arhinencephaly were categorized as having syndromes. Of the case infants with non-syndromic holoprosencephaly, 55% had malformations not attributable to the underlying brain defect. The rate of holoprosencephaly and arhinencephaly increased from 0.58 per 10,000 during 1968-1972 to 1.2 per 10,000 during 1988-1992 (P for trend = 0.016). Rates were higher for females than for males (risk ratio = 1.45, 95% C.I. 0.88-2.41) and higher for nonwhites than for whites (risk ratio = 1.74, 95% C.I. 1.06-2.86). There was a U-shaped distribution of risk associated with maternal age with a slightly increased risk for younger women (risk ratio for maternal age < 20 years, compared with age 25-29 years = 1.68, 95% C.I. 0.77-3.62) and older women (risk ratio for maternal age > 34 years, compared with age 25-29 years = 2.30, 95% C.I. 0.93-5.7), but this was not statistically significant. The increased risk in the older age group could be largely explained by the presence of cases with autosomal trisomies. Neonatal mortality was higher for infants with malformations that were not attributable to the underlying brain defect and for infants with syndromes than for infants with isolated holoprosencephaly. This analysis is the first population-based study with long-term data on this rare defect. Further epidemiologic studies will be necessary to assess the risk factors for holo-prosencephaly and arhinencephaly.

Epidemiology of congenital hydrocephalus in Utah, 1940-1979: report of an iatrogenically related "epidemic"

As part of an epidemiological study of congenital hydrocephalus in Utah, we focused on the effect of ascertainment sources and temporal variability to further delineate the causes of this relatively common, handicapping birth defect. The incidence and distribution of 934 reported cases diagnosed prior to age 6 months, and born to Utah residents from 1940 to 1979, were analyzed. Data were ascertained by examination of multiple sources, e.g., 982,066 birth, 11,161 fetal death, and 248,208 death certificates, and selected hospital and clinic records. Of the 934 reported cases, 700 met our selection criteria for congenital hydrocephalus, which results in a crude incidence of 0.70 per 1,000 live and stillbirths. Seventy-one cases (10.1%) had additional, multiple congenital anomalies. The male/female sex ratios of the 619 cases of isolated congenital hydrocephalus (occurring as a single entity or in the absence of other reported or known birth defects) and those with multiple congenital anomalies (71 cases) were virtually identical, being 1.45 and 1.48, respectively. A significant 85% increase in the rate of reported cases was observed for the period 1966 to 1970. However, examination of patients' records from 1966 to 1975 in the hospital responsible for almost all of this increase suggests that this was an iatrogenically related "epidemic" caused by several factors: the introduction and possible misinterpretation of pneumoencephalograms (PEG) in the diagnosis of hydrocephalus (PEG was replaced by CAT scanning in the early 1970s), inappropriate diagnosis, and incorrect recording of age at time of diagnosis.

Perinatal mortality and prevalence of major congenital malformations of twins in Taipei city

In order to examine perinatal mortality and prevalence of major congenital malformations in twins, deliveries in four teaching hospitals in Taipei City were studied. Among a total of 73,264 deliveries from October 1985 to June 1989, there were 844 pairs of twins. The zygosity of the twin pairs was determined by sex, placentation and 12 red blood cell antigens. There were 482 MZ and 252 DZ twin pairs identified, but the zygosity of a further 110 twin pairs was indeterminable due to lack of information on plancentation and/or blood types. A total of 4,573 singletons delivered in one study hospital from July 1986 to June 1987 were also studied as controls. The perinatal mortality rate was 7.5% for MZ twins, 1.4% for DZ twins, and 0.7% for singletons. The concordance rate of perinatal death was significantly higher in MZ (60%) than in DZ (0%) twins. The prevalence of major congenital malformations was 2.7% for MZ twins, 1.0% for DZ twins, and 0.6% for singletons. The concordance rate of major congenital malformations was 18% for MZ twins, but no DZ pair was concordant in any major congenital malformation. The concordance rate of facial clefts was 29% for MZ twins. There were 2 sets of conjoined twins giving a prevalence rate of 2.7 per 100,000 deliveries. These findings showing the prevalence of perinatal mortality and major congenital malformation to be highest in MZ twins, intermediate in DZ twins and lowest in singletons, suggest the importance of intrauterine environments in the determination of perinatal mortality and congenital malformations.

Easily identifiable congenital malformations in children: Survey of incidence and pattern in 32,332 live born neonates

Over a period of two years, 32,332 live-born infants were screened for the presence of identifiable congenital malformations. Congenital anomalies were present in 2.38% of all infants; major and minor malformations were present in 79% and 21% of the cases, respectively. Anomalies in general and chromosomal anomalies in particular were more common in multiparous women of advanced age. Anatomical organs most frequently affected were musculoskeletal and cardiovascular systems; talipes, chromosomal anomalies and congenital cardiac defects being the most common. The incidence of congenital anomalies in infants of diabetic mothers was 13.8% compared with 3% in the non-diabetic population (P=<0.01); multiple anomalies were present in 50% of the cases. Of a total of 770 infants born with malformations, 58 died during the early neonatal period with a mortality rate of 7.5% compared with an overall early neonatal death rate of 11.8/1000 live births.

Birth prevalence of Down's syndrome in England and Wales

The natural birth prevalence of Down's syndrome for England and Wales in 1974-1987 (i.e., the birth prevalence in the absence of prenatal diagnosis and the induced abortion of affected pregnancies) was estimated by applying the maternal age-specific birth prevalence derived from epidemiological studies to the number of births in single-year age groups tabulated by the Office of Population Censuses and Surveys (OPCS). On average, the natural birth prevalence was 12.6 per 10,000 births and increased slightly from 12.2 to 13.2 per 10,000 births over the 14-year period. Using data on induced abortions carried out on account of Down's syndrome reported to OPCS under the statutory abortion notification scheme, 14 per cent of affected births were avoided by the induced abortion of affected pregnancies, so that the actual birth prevalence of Down's syndrome was estimated at 10.8 per 10,000 births. Using data on Down's syndrome births reported to OPCS under the voluntary congenital malformation notification scheme, the prevalence was 7.2 per 10,000 births, so only 67 per cent of the estimated number of affected births were, in fact, notified to the scheme.

Fallacies of international and national comparisons of disease occurrence in the epidemiology of neural tube defects

Despite extensive research, little progress has been made in elucidating the etiologies of anencephalus and spina bifida. International and national distributions of disease occurrence have often been used as a basis for generating etiological hypotheses (e.g., potato blight, tea consumption, and zinc deficiency hypotheses). However, few of the epidemiological studies of neural tube defects (NTDs) have been conducted with scientific rigor in design, and most are of dubious validity, often with low precision in the estimates. This paper shows that the accepted geographic patterns of NTDs may be attributable to variations in the validity of studies used to describe these patterns. The nonuniformity in the duration and diligence of case ascertainment, the lack of a standardized nomenclature and classification, and the definition of the denominator remain principal problems in evaluating the epidemiology of NTDs. For example, the distinction between incidence and prevalence is not always made, and there is no consistency in the placement of the gestational boundary between late fetal deaths and spontaneous abortions. Findings are compared from studies conducted at different times, without due regard to the effect of secular trends, and using studies that have varying levels of case ascertainment. In etiological research, it is important to perform studies that are accurate and precise, but the literature used to define the spatial distribution of NTDs has often been accepted without due regard to the effect of these factors.

Conjoined twins in Hungary, 1970-1986

The total prevalence of conjoined twins (birth + prenatally diagnosed) was 1:68,000 in the study of 1970-1986. Symmetrical cases (the so-called siamese twins) have an obvious predominance (92.3%). Associated major malformations occurred in 80% of conjoined twins and more than 1/5 were discordant. The surviving time of liveborn conjoined twin sets was not more than two days except in two surgically successfully separated pairs. The family study did not indicate a higher recurrence risk. The case group was compared to two control groups and it appeared that the periconceptional use of oral contraception and ovulation induction were mentioned more frequently in pregnancies resulting in conjoined twins.

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.

Racial variations in the incidence of Trisomy 21

A retrospective study compared the incidence of Trisomy 21 in immigrant Asians and indigenous Europeans, aged 40 years and over and delivered in the South Birmingham Health District over a 10 year period. A significantly lower (P less than 0.01) incidence of Trisomy 21 was observed in the Asian group than was expected, whereas the indigenous Europeans showed no significant difference from other European studies.

Conjoined twins in the united states, 1970-1977

The descriptive epidemiology of conjoined twinning in the United States was investigated using data from the Birth Defects Monitoring Program (BDMP), a nationwide congenital malformations surveillance system that monitors discharge diagnoses associated with a third of the births in the United States. This is the largest recorded series concerning conjoined twins; data were analyzed on 7,903,000 births monitored by the BDMP in the period 1970-1977. The analysis identified 81 sets of conjoined twins, for a crude incidence of 10.25 per million births. The most common types of conjoined twins were thoracoomphalopagus (28%), thoracopagus (18%), omphalopagus (10%), parasitic twins (10%), and craniopagus (6%). Conjoined twins are more common among females than males, and in nonwhites than whites. No maternal age effect was found. There was no evidence of seasonal or temporal clustering of the cases. The large number of conjoined twins who had birth defects that are not obviously linked to the conjoining (particularly neural tube defects and orofacial clefts) may provide insights into the pathogenesis of birth defects resulting from disordered embryonic migration and fusion.

Differences between the events preceding spina bifida and anencephaly

It is usually held that there is a time continuum in the formation of monoxygotic (MZ) twins which is indexed by their placentation, running from dichorionic to monochorionic diamniotic to monochorionic monoamniotic and conjoined pairs. There is good evidence that this continuum is characterised by a continuum of predisposition to anencephaly, slightly raised in dichorionic pairs but very high in some sorts of conjoined pairs. Although MZ twins, especially monoamniotic and conjoined pairs, are peculiarly liable to anencephaly, they are not particularly susceptible to spina bifida. Among twin pairs concordant for anencephaly or spina bifida, there are strikingly few concordant in the sense of one twin having anencephaly and the other spina bifida, in contrast with the numbers of pairs concordant for the same malformation. The prevalence of anencephaly in double monsters varies with the type of monster, being high in diprosopus. These findings may be explained by the timing of embryonic events.

Medical genetics in China

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Differences in maternal age-specific rates of Down syndrome between Jews of European origin and of North African or Asian origin

Rates of Down syndrome in livebirths in West Jerusalem in 1964-1975 were studied in relation to the mother's continent of birth or, if she was born in Israel, to the maternal grandfather's continent of birth. In women of European origin the crude livebirth rate of Down syndrome was 1.3 per 1,000 livebirths. This crude rate and the maternal age-specific rates in this group were very close to those observed in a Swedish study and two studies of white livebirths in the United States. For West Jerusalem women of North African or Asian origin the crude rate was about 2.4 per 1,000 livebirths, and at all maternal ages except the youngest their rates were higher than for women of European origin. The summary adjusted relative risk for a Down syndrome livebirth for all those of North African or Asian origin, compared to those for women of European origin, was about 1.56. If attention is restricted to mothers born outside of Israel, the adjusted relative risk for mothers born in Europe, the Americas or English speaking countries of the British commonwealth compared to those born in North Africa or Asia was 1.97, consistent with a two-fold difference in the likelihood of a Down syndrome livebirth between thes two groups. To our knowledge this is the first report of ethnic differences in maternal age specific rates of Down syndrome that cannot be plausibly explained by differences in ascertainment.

The sex ratio in anencephaly

A review of the data supports the suggestion of Knox (1974) that the sex ratio and incidence of anencephalics vary together within populations, as they are known to do between populations. There seems some doubts, though, whether Knox was correct in hypothesising that the sex ratio of anencephalics varies with their incidence in relation to the dizygotic twinning rate. The pattern of variation seems to suggest that there are two sorts of cause of anencephaly, one of which is environmental and affects predominantly female embryos. The other may be environmental or genetic, and seems to attack the sexes in roughly equal numbers. If this hypothesis were correct, it would carry implications for the testing of specific teratogens.

Incidence rates for cleft lip and palate in British Columbia 1952-71 for North American Indian, Japanese, Chinese and total populations: secular trends over twenty years

The incidence of cleft lip and/or cleft palate was examined for the 1952-71 period for the Province of British Columbia. Although there were some fluctuations, some of which were significant, there was no general trend which indicated that the rates were either increasing or decreasing. These rates are important for a background calculation when investigating new invironment teratogens. The total rate of 1.97 per 1,000 live birth is comparable with other Caucasian populations where there is good ascertainment and adequate follow-up period. This study also confirmed the previously reported high rate for North American Indians in British Columbia (3.74 per 1,000 live births) and established rates for the Japanese (3.36 per 1,000 live births) and Chinese (1.76 per 1,000 live births) of British Columbia. Since these three sub-populations are relatively small in relation to the total population, they do not influence the overall total rate to any great extent.

Holoprosencephaly in human embryos: epidemiologic studies of 150 cases

One hundred fifty embryos with holoprosencephaly were found among the total of 36,380 conceptuses obtained through induced abortion in the period from 1962 to 1974, giving an overall incidence of 0.4 percent. The occurrence was period from 1962 to 1974, giving an overall incidence of 0.4 percent. The occurrence was largely at random through time, and no "epidemic" was noted in particular years or months, but there appeared more cases derived from conceptions in winter than in summer months. The mean maternal age did not differ significantly from that of the general embryonic population, indicating that, although none of our cases were karyotyped, chromosome aberrations such as trisomies 13 and 18 that are closely associated with maternal age may not constitute a major part as causes of holoprosencephaly in human embryos. Materal age did not differ by the presence or absence of associated external anomalies. No association was found with paternal age, parental consanguinity nor with maternal medical history, including irregularity of menstrual cycles, and smoking and drinking habits. There was an indication that the mothers were prone to have repeated miscarriages, supporting the view that some kind of maternal predisposition is responsible for the causation of holoprosencephaly. Argument was made that, apart from various chromosome aberrations well documented as causes of this malformation, polygenic mechanism probably accounts for the majority of the cases with normal karyotype.

Twin studies in medical genetics

It is the aim of twin studies to obtain results which are not only valid for twins, but apply to the whole population. Therefore the following questions have to be answered first: do twins differ from non-twins in the trait under study? Do different nongenetic factors act upon MZ and DZ twins which alter the probability of manifestation of a trait, even before birth? There are important differences in embryogenesis and placental blood flow in mono- and dichorionic twins; this can influence the normal fetal development. Therefore the value of twin studies alone in analysing the genetic component in the etiology of congenital malformations is rather ambiguous. Twin studies beyond the newborn period can be classified into four approaches: (1) Case reports; (2) Accumulated case reports; (3) Limited representative sample; (4) Unlimited representative sample. The most frequent systematic method in medical genetics is the establishment of all twins in a defined population of probands (3). Another successful application in the last few years has been in pharmacogenetics. Although no simple mode of inheritance could be discovered, it was possible to estimate the genetic component within the interindividual variability of the metabolism of certain drugs (nortriptyline, antipyrine, phenylbutazone, ethanol). Now, additional non-twin research is needed to work out single factors within the observed polygenic systems.

Induced abortion and subsequent outcome of pregnancy. A matched cohort study

The effect on subsequent pregnancy outcome related to abortion was studied in a sample of 26,000 births in Taiwan. When no adjustment was made for confounding maternal variables, significant relationships were found between previous abortion and various problems of outcome of subsequent pregnancies. However, in a matched-pair cohort study controlling for relevant maternal characteristics, all such relationships disappeared. It is concluded that the deleterious effects of abortion on subsequent pregnancy outcome reported by others may be a consequence of the failure to adjust for maternal factors which are related both to abortion status and pregnancy outcome, and not to abortion itself.