M.L. Martínez-Frías

Congenital eye malformations : Clinical-epidemiological analysis of 1,124,654 consecutive births in Spain

We analyzed Spanish Collaborative Study of Congenital Malformations (ECEMC) data on a series of 1,124,654 consecutive births to study congenital eye malformations from an epidemiological standpoint. We studied their frequencies as well as some causal and clinical aspects. Four hundred fourteen infants had eye malformations, for an overall prevalence of 3.68/10,000 newborns. Most frequent were: anophthalmia/microphthalmia (21.34/100,000), congenital cataract (6.31), coloboma (4.89), corneal opacity (3.11), and congenital glaucoma (2.85). In our data, the tendency of eye malformations to be associated with other congenital abnormalities is evident (only 21.01% of cases were isolated). Eye defects are heterogeneous, since we have observed them in clinical patterns with all modes of inheritance or caused by different environmental agents. Chromosomal syndromes represent 60% of total syndromes, followed by syndromes of autosomal-recessive inheritance (15%), environmental syndromes (10%), autosomal-dominant syndromes (5.83%), and other types which have a lower frequency. Regarding defects associated with eye malformations, most frequent are limb anomalies (affecting 59.3% of multiply malformed cases), auricular/facial (47.1%), central nervous system (42.5%), osteomuscular excluding limbs (42.2%), genital defects (30.6%), oral clefts (29.4%), and the rest of the body systems, which are less frequent. Using the method outlined by Prieto and Martínez-Frías [1996: Am J Med Genet 62:61-67], it was demonstrated that the association of coloboma and anophthalmia/microphthalmia was specific, as was the combination of cataract and anophthalmia/microphthalmia, and that of anophthalmia/microphthalmia with holoprosencephaly. From these statistical associations some pathogenetic relationships in human embryos can be inferred, supporting several previously proposed mechanisms.

Epidemiological analysis of outcomes of pregnancy in gestational diabetic mothers

The association between maternal diabetes mellitus and congenital defects has been well documented. However, few data exist on the potential teratogenic effect of gestational diabetes (GD). We analyzed 19,577 consecutive infants with malformations of unknown cause and compared the offspring of mothers with GD with those of nondiabetic mothers. The children with each of 20 types of selected anomalies among the two groups were used to calculate the odds ratio (OR). Because we used as a reference group for each congenital defect the rest of malformed infants, the value of the OR gives us the specificity between the association of GD and each congenital defect. Our analysis strongly supports the suggestion that GD is a significant risk for holoprosencephaly, upper/lower spine/rib, and renal and urinary system anomalies. GD is a heterogeneous disorder, which includes previously unrecognized and newly diagnosed nongestational diabetes mellitus (DM). Thus, it is possible that the teratogenic effect is related to latent DM. However, because it is not possible at this time to differentiate between these situations, pregnancies complicated by GD should be considered at risk for congenital anomalies. Prenatal ultrasound examination should be aimed particularly at the detection of abnormalities of the central nervous system, the renal and urinary system, and the spine/rib developmental field.

Prenatal exposure to salicylates and gastroschisis: A case‐control study

Gastroschisis, which is a defect in the abdominal wall, lateral to the umbilical cord, is considered to be a vascular problem, probably due to a disruption of the omphalomesenteric artery [Hoyme et al. (1981) J. Pediatr. 98:228-231]. Recently, Torfs et al. [(1996) Teratology 54:84-92] observed a significantly increased risk for aspirin and ibuprofen, two strong cyclooxygenase inhibitors. Here we present the results of a case-control study conducted by the Spanish Collaborative Study of Congenital Malformations (ECEMC) on the relationship between prenatal exposure to salicylates during the first trimester of pregnancy and gastroschisis. The results show an increased risk (OR = 3.47; P = 0.015) after controlling the possible effect of maternal age and maternal smoking during pregnancy.

Maternal polymorphisms 677C-T and 1298A-C of MTHFR, and 66A-G MTRR genes : Is there any relationship between polymorphisms of the folate pathway, maternal homocysteine levels, and the risk for having a child with down syndrome?

This study was aimed at analyzing the effect of mutations in three non‐synonymous SNP genes (677C > T and 1298A > C of the methylenetetrahydrofolate reductase (MTHFR) gene, and 66A > G in the MTRR gene) on total plasmatic homocysteine (Hcy), in 91 mothers of Down syndrome (DS) infants and 90 control mothers. The comparison of both groups of mothers is a new way to determine if those mutations and their interactions increase the risk for DS. Material came from the case‐control network of the Spanish Collaborative Study of Congenital Malformations (ECEMC).

Limb defects associated with major congenital anomalies: clinical and epidemiological study from the International Clearinghouse for Birth Defects Monitoring Systems.

Although limb defects associated with other congenital anomalies are rarely studied, they may provide insights into limb development that may be useful for etiologic studies and public health monitoring. We pooled data from 11 birth defect registries that are part of the International Clearinghouse for Birth Defects Monitoring Systems. We identified 666 infants, born from 1983 through 1993, who had a non-syndromal limb defect plus at least one other major malformation (rate 12.9/100,000 population). We used observed/expected ratios and log-linear models to detect association patterns. We found that specific limb defects occurred with relatively distinct sets of malformations. Preaxial limb defects occurred more frequently with microtia, esophageal atresia, anorectal atresia, heart defects, unilateral kidney dysgenesis, and some axial skeleton defects; postaxial defects with hypospadias; transverse defects with craniofacial defects, micrognathia, ring constrictions, and muscular defects; intercalary defects with omphalocele; split hand/foot with encephalocele; and amelia with anorectal atresia, omphalocele, severe genitalia defects, unilateral kidney dysgenesis, gastroschisis, and ring constriction. Log-linear modeling identified higher order associations among some of these same malformations.

Increased parental age and number of pregnancies in Klippel–Trenaunay–Weber syndrome

The Klippel–Trenaunay–Weber syndrome (KTWS) is generally thought to occur sporadically, following a somatic mutation model. However, in some cases, clinical manifestations of the syndrome have been found in family members, suggesting an autosomal dominant inheritance. Here we present an epidemiological analysis of a consecutive series of cases with KTWS identified in the Spanish Collaborative Study of Congenital Malformations (ECEMC). We found an increase in parental age and in the number of pregnancies, as well as familial occurrence of haemangiomas. These observations suggest a genetic contribution to the occurrence of KTWS.

The Biochemical Structure and Function of Methylenetetrahydrofolate Reductase Provide the Rationale to Interpret the Epidemiological Results on the Risk for Infants With Down Syndrome

Studies on the structure of the methylenetetrahydrofolate reductase (MTHFR) gene and the mechanisms by which folate may reduce homocysteine levels in bacteria and in humans have provided a rationale to understand the conflicting epidemiological observations between the studies on the 677C‐T and 1298A‐C MTHFR polymorphic variants, and the risk of having an infant with Down syndrome (DS). However, three of the combined genotypes (CTCC, TTAC, and TTCC) are very infrequent in the human population. In fact, these three rare genotypes were only observed in two of the eight epidemiological studies that analyzed these genotype combinations and the risk of DS. In a study of the Indian population these three genotypes were identified in mothers of DS children but not in control mothers demonstrating a statistically significant increase in the risk of giving birth to DS infants. Conversely, the CTCC and TTAC genotypes were only observed in control mothers and not in mothers of DS infants in the Spanish study, while the TTCC genotype was not observed in any Spanish mother analyzed. These results were not related to the frequency of the T allele, since this was lower in the Indian population (21.4% among case mothers and 12.4% in control mothers) than in the Spanish population (33.9%). At present, several important biological aspects on the Hcy cycle are known, including: (a) the biochemical structure and function of the MTHFR enzyme, (b) the biological basis for the effect of the different 677C‐T and 1298A‐C MTHFR genotype combinations on Hcy levels, (c) that folate is not synthesized by the organism that obtained it from the diet, (d) that TT homozygotes will be at particular risk when their folate status is low because the mutant enzyme requires much higher levels of folate than the physiological one to stabilize the binding of flavin‐adenosine‐dinucleotide (FAD), (e) that the release of flavin is prevented by increasing the levels of folate, and (f) that the cystathionine‐beta‐synthase gene is located on chromosome 21. Together, these facts suggest that destabilization of the Hcy cycle in function of the levels of S‐adenosylmethionine (SAM), may be modified by some embryonic and maternal genotypes, as well as by maternal nutritional status and life style. This may also influence the probability that some embryos survive to birth, but in different way for those with and without trisomy 21, as is discussed in this article.

High maternal fever during gestation and severe congenital limb disruptions

Hyperthermia is defined as a temperature of at least 1.5 degrees C over the normal core body temperature. It is a proven teratogen in animals and in humans. The type of defects induced by hyperthermia in experimental animals are: anencephaly/exencephaly, encephalocele, microphthalmia, arthrogryposis, abdominal wall defects, limb deficiencies, embryonic death, and resorption. In humans it has been observed that infants prenatally exposed to hyperthermia presented with spina bifida, encephalocele, microphthalmia, micrognathia, external ear anomalies, cardiac defects, hypospadias, gastrointestinal defects, cleft lip and/or cleft palate, abdominal wall defects, diaphragmatic hernia, Hirschsprung disease, Möbius syndrome, oromandibular-limb hypogenesis spectrum, and spontaneous abortions. We describe an additional case with severe limb deficiencies whose mother had fever over 39 degrees C for 2 days in the second and in the fourth month of amenorrhoea. We conclude that, based on the degree of development of the humeri and the femora and the type of limb deficiencies, this case presents a disruption that most probably occurred in the fourth month of gestation.

Clinical and epidemiological characteristics of infants with body wall complex with and without limb deficiency

The spectrum of defects in cases with limb body wall complex (LBWC) is quite variable since other anomalies are also observed in infants with LBWC, and some cases do not have limb deficiencies. Van Allen et al. [Am J Med Genet 1987;28:529-548] proposed that the diagnosis of LBWC (presence of body wall defects with evisceration of thoracic and/or abdominal organs, limb deficiency, and myelocystocele) should be based on the presence of two of three of the following anomalies: exencephaly or encephalocele with facial clefts, thoraco and/or abdominoschisis, and limb defects. This approach implies that an infant with encephalocele with facial clefts and limb defects may be considered as having LBWC, which I do not think is correct. I present the results of a clinical and epidemiological analysis aimed at identifying if, from an epidemiological perspective, it is possible to identify an entity which is characterized by the presence of abdominal wall defects along with other malformations including or not limb deficiencies. The result of this analysis allows us to consider that this entity should be characterized by the presence of abdominal wall defects with a variable spectrum of anomalies (with or without limb deficiencies) and, consequently, be called body wall complex (BWC). BWC includes cases regardless of their clinical pattern and the possible etiology or pathogenetic mechanism. Thus, the BWC entity does not include amniotic band sequence without body wall defects, but does include amniotic band sequence with body wall defects.

Anal atresia, vertebral, genital, and urinary tract anomalies: A primary polytopic developmental field defect identified through an epidemiological analysis of associations

Anal atresia (AA) is observed per se or as part of different Mendelian or chromosomal syndromes, and as part of the VACTERL primary developmental field, CHARGE association, cloacal extrophy, in a mitochondrial cytopathy, and other multiple congenital anomaly patterns. There are only a few studies on the defects associated with AA, and in all of them it was observed that genitourinary defects are most frequent in infants with AA. Here we present the analysis of 28,410 malformed infants to study the frequency of 11 selected congenital defects in infants with AA in relation to their frequency in infants with multiple congenital anomaly patterns without AA. We conclude that the association of AA + spine defects + renal/urinary tract defects + genital defects constitutes a group of defects that tends to be present together in the same child because they are pathogenetically related, and since they are of blastogenetic origin they constitute a primary polytopic developmental field defect.