Long-term outcome in open spina bifida.

BACKGROUND: Doctors need reliable data on outcome in order to help parents faced with difficult decisions about termination of an affected pregnancy or treatment after birth. AIM: To determine survival, health and lifestyle at the mean age of 30 years in a complete cohort of adults born with open spina bifida. DESIGN OF STUDY: Prospective cohort study. PARTICIPANTS: Well-documented cohort of 117 consecutive cases of open spina bifida whose backs were closed non-selectively at birth between 1963 and 1971. METHOD: Survivors (age range = 26 to 33 years) were surveyed by postal questionnaire and telephone interview. The main outcome measures were the health, independence and lifestyle of the survivors in terms of living in the community, driving a car and working in open employment. RESULTS: Ascertainment was 100%. Sixty (51%) had died, mainly the most disabled. Of the 57 survivors, 84% had a cerebrospinal fluid (CSF) shunt, 70% had an IQ of 80 or more, 37% lived independently in the community, 39% drove a car, 30% could walk more than 50 metres and 26% were in open employment. However one-third (19) still needed daily care, three were on respiratory support, two were blind, two had diabetes mellitus, and one was on dialysis. Mortality, disability and achievement reflected the neurological deficit that had been recorded in infancy in terms of sensory level. Attainment and independence were reduced in those who had needed revision of CSF shunt. CONCLUSION: The survivors in this unselected cohort showed a wide range of outcome from apparent normality to very severe disability. This reflected both the extent of their original neurological deficit and events in the history of their CSF shunt.     

Parental sex effect in spina bifida: a role for genomic imprinting?

Fifty families (491 individuals in 137 sibships) with more than one living case of isolated, nonsyndromic spina bifida (SB) were analyzed genetically. There were twice as many gene-carrier females (56) as gene-carrier males (28) (P < 0.005). This was not an artifact of ascertainment bias because the sex ratio of gene-carriers was the same whether the pedigree was obtained through the proband's father or mother. Also, this effect was not observed in other disorders analyzed by the same method. Neither was the effect due to differential fertility because the number and sex of affected and unaffected children per gene-carrier parent were not different for male or female gene-carrier parents. There was no evidence that the missing male gene-carriers were lost by selective spontaneous abortion. There was no deficit of male-to-male or male-to-female transmission, excluding simple X-linked or simple mitochondrial inheritance. If genomic imprinting plays a role in the unequal female and male carrier frequencies in SB, penetrance should differ with parental sex. Penetrance was higher for offspring of female parents than of male parents, but the difference was not statistically significant. In addition, both male and female gene-carriers were frequently found in the same pedigree. Thus, the present data suggest a possible role for imprinting in SB.     

Catecholamine metabolite excretion in spina bifida

The urinary excretion of vanilmandelic acid (VMA), homovanillic acid (HVA), and parahydroxyphenylacetic acid (pHPAA) was measured in 55 children with meningomyelocoele selected at random. In 96% of the children the levels of one or other of these compounds was significantly raised above the normal, usually by a factor of about 3. High VMA levels usually meant high HVA levels but the values for pHPAA appeared to be quite independent of the others. These results suggest a disorder of tyrosine metabolism, and the possible implications are discussed.     

Shifting genetic patterns in anencephaly and spina bifida.

The long-term decline in the incidence of the neural tube malformations, anencephaly and spina bifida (ASB), ended in the mid-1950's in New York State. Since that time, the rate of these birth defects has remained between 1 and 1.5/1000 births. In this low incidence population, we tested the basic tenets which support a genetic aetiology. We found that the full sib recurrence rate (1.8%) was higher than the half sib recurrence rate (0.8%) and the twin concordance rate (6.8%) was higher than the full sib recurrence rate. We found the incidence of ASB in twins to be the same as the incidence of ASB in singletons. Our findings are compatible with polygenic inheritance aetiology for ASB. The genetic molecular pathway of these birth defects may be identifiable through biochemical screening of families with one or more ASB children.     

Genetic spina bifida occulta in the mouse

Spina bifida occulta is one of the major effects of the recessive mutant “snubnose” (symbol sno). Linkage tests have located this mutant in chromosome 4. Defective spinal arch formation typically includes the lumbar and often the posterior thoracic and sacral vertebrae. There is great variation in detail, from nearly normal closure to a trough-like spinal column. Causes of the variation are not understood. Severely affected specimens may also have defective anterior thoracic vertebrae and reduced size of the sacral vertebrae, with kyphosis. The tail is essentially normal. No external lesion or myelomeningocele has been found, but there have been some instances of paralysis of the hind limbs, possibly from injury. The spinal cord seems normal as a rule, and pigmentation is normal. Embryological study has not been attempted, but the condition seems to be primarily osteogenic in origin.     

Morphology of experimental spina bifida in the chick embryo.

Open malformations of the central nervous system may involve the brain or spinal cord, or both. Preliminary experiments in which a window was cut in the shell overlying early chick embryos (with removal of 2 ml of albumen) produced a range of neural and non-neural malformations. Exposure of Stage 5--10 embryos at 26 hours of incubation produced open brain and cord defects. Embryos were recovered at 11--12 days for gross examination. Open cord defects in 12 day experimental embryos could be divided morphologically into 2 types. One group showed an everted symmetrical plaque of neural tissue. In the other group the cord defect was more irregular, partly covered by skin, and often combined with rump and trunk defects. Skeletal staining showed that vertebral lesions increased in severity in a cranio-caudal sequence. Spina bifida occulta was found in the cervical and upper thoracic regions; spina bifida manifesta, associated with open cord defects, occurred from the lower thoracic to the sacral regions; vertebral deletions were almost confined to the caudal region. Spina bifida manifesta at the site of open cord defects also showed 2 distinct patterns. Regular cord defects were associated with regular spinal defects, showing loss of spinous processes, reduction of laminae and eversion of the pedicles. Irregular cord defects were associated with more irregular spinal defects showing vertebral deletions or fusions, rumplessness, and pelvic reduction. Neither group, however, showed local kyphosis or scoliosis. Early neurogenesis in the avian and human embryos is very similar with development of the spinal cord from neural plate and tail bud materials which fuse in an overlap zone. These experimental defects in the chick embryo, separable into regular and irregular types thus provide a useful model for investigation of the embryogenesis of spina bifida.     

Possible causal heterogeneity in spina bifida cystica

A study was performed to determine whether causal heterogeneity can be demonstrated among the nonsyndromal spina bifida cysticas based on the vertebral level of the defect. Two groups were compared, probands with defects at or above T 11, likely representing defects of neuralization, and probands with defects at or below T 12, likely defects of canalization. Differences between the two groups were found with respect to reproductive history and occurrence of other malformations. A high degree of concordance for the type of defect among affected sib pairs was also observed. These findings indicate that there is probably heterogeneity within the spina bifida cysticas based on the level of the defect.     

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.     

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.