Brief clinical report: neural tube defects in dup(11q)

Chromosomal abnormalities associated with neural tube defects (II): partial aneuploidy

Fetuses with neural tube defects (NTDs) carry a risk of chromosomal abnormalities. The risk varies with maternal age, gestational age at diagnosis, association with other structural abnormalities, and family history of chromosome aberrations. This article provides a comprehensive review of structural chromosomal abnormalities associated with NTDs, such as del(13q), r(13), dup(2p), del(2q), del(1p), del(1q), dup(1q), del(3p), dup(3p), del(3q), dup(3q), del(4p), dup(4p), del(4q), dup(4q), del(5p), del(6p), dup(6q), del(6q), dup(7p), del(7q), dup(8q), del(9p), del(10q), del(11q), dup(11q), dup(12p), dup(14q), del(14q), del(15q), dup(16q), del(18q), r(18), dup(20p), +i(20p), del(22q), del(Xp), and dup(Xq). NTDs may be associated with aneuploidy. Perinatal identification of NTDs should alert one to the possibility of chromosomal abnormalities and prompt a thorough cytogenetic investigation and genetic counseling.

Non-multifactorial neural tube defects

Although most neural tube defects (anencephaly, spina bifida) occur as isolated malformations, a substantial proportion are attributable to chromosome anomalies, known teratogens, or component manifestations of multiple anomaly syndromes. This review describes known chromosome alterations and the candidate genes residing in the altered region, as well as syndromes associated with neural tube defects and causative genes, if known.

Fetal penile length

OBJECTIVE

To construct a reference range for fetal penile length.

METHODS

The length of the penis was measured during ultrasound assessment of 95 structurally normal male fetuses of gestational ages 16-38 weeks. Two fetuses with bladder outflow obstruction were also examined.

RESULTS

Fetal penile length increases significantly with gestational age, from a mean value of 6.0 mm at 16 weeks to 26.4 mm at 38 weeks. One fetus with urethral agenesis had a penile length on the 0.3rd centile.

CONCLUSIONS

Measurement of the fetal penis is easy and not time-consuming. In cases of bladder outflow obstruction, assessment of penile length assists in the differentiation between urethral agenesis and posterior urethral valves.

Prenatal diagnosis of partial monosomy 13q associated with occipital encephalocoele in a fetus

The pre- and postnatal findings of a fetus with a de novo del(13)(pter-->q21:) and an occipital encephalocoele are described. Maternal serum alpha-fetoprotein (AFP) screening at 19 weeks' gestation demonstrated a high level of 2.5 multiples of the median (MOM) and ultrasonography at 27 weeks' gestation showed severe intrauterine growth retardation, cardiomegaly, an occipital encephalocoele, and a calvarial defect. Genetic amniocentesis revealed a karyotype of 46,XX,del(13)(pter-->q21:). The proband postnatally displayed additional abnormalities such as microphthalmia, hypertelorism, large low-set ears, and micrognathia. We discuss the association of central nervous system (CNS) malformations with 13q deletions and emphasize that pregnancies with neural tube defects warrant cytogenetic analysis, especially when additional fetal abnormalities and neonatal dysmorphism are observed.

Autosomal imbalance syndromes: genetic interactions and the origin of congenital malformations in aneuploidy syndromes

In some autosomal imbalance syndromes an additional imbalance interferes with the occurrence of the anomalies typical of the syndrome itself. For example, polydactyly was found in patients with "pure" del(3p) more frequently (11/23) than in patients where these deletions were associated with different partial trisomies (2/28). The opposite situation was shown in del(7q) syndrome where various defects of the holoprosencephalic group were found to be rarer in patients with "pure" deletions, than in cases with simultaneous occurrence of various partial trisomies. It suggests the importance of gene interaction in determining the phenotypic picture of autosomal imbalance syndromes.

Familial t(11;13)(q21;q14) and the duplication 11q, 13q phenotype

Cases of duplication of distal 11q or proximal 13q have been reported independently. A specific translocation resulting in duplication of distal 11q, [der(22)t(11;22)(q23;q11)], has been documented in over 40 cases. We report on a male fetus with chromosomal excess of both distal 11q and proximal 13q resulting from a familial translocation. This case supports the causal association of duplication 11q with neural tube defects.

Congenital cardiovascular malformations (CCVM) and structural chromosome abnormalities: a report of 9 cases and literature review

Nine cases of congenital cardiovascular malformations (CCVM) with associated unbalanced structural chromosomal abnormalities were ascertained in a population-based study of heart defects, constituting 0.4% of the 2,103 cases of CCVM in the Baltimore-Washington Infant Study (BWIS). This represents a four-fold increase over the general population rate. In an effort to determine possible phenotype/karyotype correlations, the literature was searched for cases with similar karyotypic abnormalities. This comparison of 223 literature cases of karyotypic abnormalities with nine similar cases ascertained by heart malformation has provided the opportunity to review cardiac defects reported in cases of structural abnormalities of chromosomes 1, 3, 7, 8, 9, 10, 11, 15, and 18. The most common cardiac malformation present in the chromosomal cases was ventricular septal defect (VSD) (39%); similarly VSD is the most common CCVM among children with heart defects, although it is the primary defect in only 20% of the BWIS cases. Among all heart defects in the BWIS, atrial septal defect (ASD) represents 5.5% of all cases, but in cases of 8p duplication, ASD is present in 41%. In addition, 40% of cases of 9p duplication had an ASD. Similarly, 35% of cases of 11q duplication had an ASD. While the suggestion of specific karyotype/phenotype association is premature, information on additional cases might clarify the possibility that genetic determinants related to septum formation may reside on chromosome 8, 9, and/or 11. The variety of chromosomal abnormalities in cases with ventricular septal defect indicates one type of genetic heterogeneity that may be involved in this very common heart defect.

The value of chromosome analysis in cases of neural tube defects: a case of anencephaly associated with fetal dup(2)(p24----pter)

A family is described in which two anencephalic fetuses were identified in two pregnancies. Autopsy revealed kidney anomalies in both fetuses. Chromosome analysis was performed only on the second fetus, which had a 46,XY,10q+ karyotype. Parental chromosome analysis showed the maternal karyotype to be 46,XX,t(2;10)(p24;q26) thus demonstrating that the fetus was carrying a duplication 2(p24----pter). Recurrence risks for anencephaly based on the cytogenetic abnormality were much higher than those which would be quoted for isolated anencephaly. This points out the necessity for complete diagnostic studies when a fetus with a neural tube defect is identified. The literature in regard to the 2p duplication phenotype is reviewed. It is possible that the duplication of the distal segment of 2p results in a neural tube defect/kidney anomaly phenotype.

Neural tube defects: a review of human and animal studies on the etiology of neural tube defects

Although neural tube defects are a common congenital anomaly, their etiology is not known. Human studies have emphasized the pathology and epidemiology of the defects and suggest that in the majority of cases the etiology is multifactorial. Factors which appear possibly to be important are genetic predisposition, maternal illness, and fetal drug exposure. Animal studies have utilized naturally occurring neural tube defects and teratologically induced lesions. No animal model has been convincingly established as the equivalent of human neural tube defects. However, animal models have allowed investigation of the mechanisms of suggested human teratogens and determination of the pathogenesis of naturally occurring animal defects. Their most important contribution has been in furthering the understanding of the normal mechanisms of neural tube closure. It may be through this understanding that the etiology of human neural tube defects will be determined.

Ultrastructural analysis of chromosome translocation-induced neural tube defects

Neural tube closure defects occurred in 33% of the embryos obtained from matings of male mice heterozygous for a reciprocal chromosome translocation (T(2;4)1Sn) with normal female CFLP mice. Light and electron microscopic observations of neuroepithelium and mesenchyme in affected embryos indicated two distinct types of anomalies occurred. The first consisted of neuroepithelial hypertrophy and neural tube closure defects. These defects most frequently affected the midbrain and hindbrain, but occasional defects of the lumbosacral neural tube were also observed. Unlike the highly organized, pseudostratified neuroepithelium in control embryos, neuroepithelial cells became stratified and formed cell islands with secondary lumina within the wall of the neural tube. The second condition was associated with a reduction in neuroepithelial thickness, considerable neuroepithelial and neural crest cell death, basal lamina alterations and premature invasion of the neuroepithelium by subjacent endothelial cells. In both cases, the cephalic mesenchyme cells, rather than their normal stellate appearance, were markedly elongated in shape and reduced in area. The number of cell-cell contacts between mesenchymal cells was also reduced significantly. These results are discussed in light of recent theories regarding the role of mesenchyme and extracellular matrix in neurulation.