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Biomedical subjects

M Melnick

Publications and source records attributed to M Melnick.

At least 91 records · Page 5Linked to original sources
PubMed1980

Estimates of genetic variance for anterior fontanelle development in the NCPP twin population.

There are several dynamic influences on anterior fontanelle development in infants; among them, brain growth, dural attachments, suture development, and osteogenesis, It thus seems reasonable to hypothesize that variation in anterior fontanelle development between infants, related and unrelated, might have a significant genetic component. Anterior fontanelle size was quantitated by the method of Popich and Smith for 94 monozygotic (MZ) and 187 dizygotic (DZ) four-month-old twin pairs. The general model for estimating genetic variance from quantitative twin data was applied to MZ and DZ twins and then separately by chorion type. Since there were significant mean differences between blacks and whites, races were analyzed separately. The within-pair mean square estimates of genetic variance (GWT) were highly significant for both blacks (less than 0.02) and whites (P less than 0.002). Comparisons of means, total variances, and among-pair mean squares within races revealed no heterogeneity. There were also no significant chorion effects. Since the anterior fontanelle closes at around 1--1 1/2 years of age, it was evaluated at age one in 95 MZ and 194 DZ twin pairs as a qualitative trait - ie, open vs closed, concordance vs discordance. There were no significant differences in proband concordance rates between MZ and DZ twin pairs for either blacks (P greater than 0.5) or whites (P greater than 0.10). Again, there were no significant chorion effects. These data suggest that anterior fontanelle developmental variation has a significant genetic variance component at four months of age but not at one year. This finding may be related to the rapid brain growth witnessed between birth and eight to nine months of age.

Anthropometry↗
PubMed1979

The effects of chorion type on normal and abnormal developmental variation in monozygous twins.

To determine the effects, if any, of chorion type on normal and abnormal developmental variation in monozygous (MZ) twins, we tested the hypothesis that disparate environments that are related to chorion type have no effect on this variation. The parameters studied included congenital anomalies and dermatoglyphics (total ridge count and right-left asymmetry). With the exception of total ridge count, analyses of these data failed to reject the null hypothesis. Dichorionic MZ twins had a significantly greater within-pair variation than monochorionic MZ twins for total ridge count. In summary, then, these data could offer little support to prior speculation that monochorial placenta may present less favorable environments for feta development.

Analysis of Variance↗
PubMed1979

Current concepts of the etiology of central nervous system malformations.

We have seen that what must be applied to dysmorphology is the doctrine of multifactorial causality, ie dysmorphogenetic events have both genetic and nongenetic etiologic components to varying degrees. Complicating matters is the extent to which there is etiologic and/or mechanistic heterogeneity (Fig. 1). This is nicely illustrated by the holoprosencephaly anomaly. In addition, there are numerous CNS malformations that have major single gene, chromosomal, or environmental initiating agents of malformation mechanisms. Still a mystery is the common neural tube malformations. It is now clear that the "multifactorial/threshold" model is an inadequate explanation of the observed data and until the etiologic heterogeneity of these malformations is clearly defined, our knowledge remains primarily empiric. A potential area of fruitful investigation is likely to be the identification of maternal genotypes which do not allow detoxification of potential environmental teratogens.

Central Nervous System↗
PubMed1978

Branchio-oto-renal dysplasia and branchio-oto dysplasia: two distinct autosomal dominant disorders.

Three families are presented, one with branchio-oto-renal dysplasia (BOR) and two with branchio-oto dysplasia (BO). The former syndrome is characterized by external ear malformations, cervical fistulae, mixed hearing loss and renal anomalies of varying severity. The latter syndrome differs in that there are no renal anomalies and that the sensorineural component of the hearing loss may be absent. The external ear malformations are quite variable in both syndromes. Evidence is presented which supports the idea that these two syndromes are not phenotypic variants of the same autosomal dominant mutation but distinct disease entities. The BOR syndrome appears to belong to a larger group of hereditary ear dysplasia-renal adysplasia syndromes that must be carefully ruled out in all patients with familial branchial arch malformations as well as in the parents and siblings of infants with "Potter facies" in the presence of auricular malformation and renal adysplasia.

Abnormalities, Multiple↗
PubMed1978

The effects of chorion type on variation in IQ in the NCPP twin population.

The 7-year IQ scores (WISC) of 116 white and 143 black nonmalformed twins of known zygosity and placental type were ascertained from the NINCDS Collaborative Perinatal Project (NCPP). The type of chorion and zygosity had no significant effect on the mean IQ or among-pair variation. In white monozygotic twins, however, analysis of variance revealed a significantly greater within-pair mean square for dichorionic twins than monochorionic twins. On the other hand, the white dichorionic monozygotic (MZ) and dizygotic (DZ) within-pair mean squares were quite similar. These findings were not evident in blacks for either of the within-pair comparisons. In addition, estimates of genetic variance were dependent upon MZ chorion type in both races. These data suggest to us that (1) in white twin pairs dichorionic placentas are of greater influence than the similarity or dissimilarity of genomes with regard to intrapair IQ development, and (2) failure to consider chorion type may introduce a serious bias in the interpretation of genetic variance estimates of IQ variability.

Chorion↗
PubMed1977

Focal odontoblastic dysplasia: dentin dysplasia type III?

A new, nonsyndromic dentin defect, focal odontoblastic dysplasia, is described on the basis of clinical, radiographic, histologic, and scanning electron microscopic criteria. A provisional classification is proposed for this disease entity according to the nosology of Shields and associates. Four additional cases in the literature which possibly represent this new entity are presented, and a possible genetic etiology is discussed.

Adult↗
PubMed1977

Dentin dysplasia, type II: a rare autosomal dominant disorder.

Dentin dysplasia, Type II, is a rare autosomal dominant disorder. The primary teeth are amber and translucent and the pulp chambers are obliterated. The permanent teeth have a normal to brown-gray coloration and a thistle-tube pulp configuration with multiple true denticles. To date, only five families with this disorder have been reported. This article presents two additional families. Light and scanning electron microscopy of an affected primary incisor showed the dentin, including the mantle layer, to be highly disorganized throughout. Possible pathogenic events associated with the phenotype are discussed.

Adolescent↗
PubMed1977

Tricho-dento-osseous syndrome: a scanning electron microscopic analysis.

A large kindred of which multiple members have the Tricho-dento-osseous syndrome is presented. This is an autosomal dominant disorder characterized by defective enamel, taurodontia, unusually curly hair and occasionally mild to moderate skeletal osteosclerosis. Histologic investigation of teeth (by both LM and SEM) demonstrated that there is a uniformly thin enamel covering with randomly distributed depression and pits. The mineral content of this enamel is closer to that of the underlying dentin, which accounts for its lack of radiographic contrast. The dentin was normal. A bizarre finding is that of a periradicular sheath or membrane that enclosed the open apices and extended partway up the root. It was composed of collagen fiber bundles. The anatomical position of this membrane suggested that it may represent the developing peridontal ligament seen in early tooth formation. Recent embryologic evidence provides support for mesenchymal culpability for all reported features of the syndrome.

Adolescent↗
PubMed1977

Maxillofacial dysostosis.

Four individuals in a single family affected with maxillofacial dysostosis are reported. Maxillary hypoplasia, delayed onset of speech, and poor development of language skills without associated hearing loss are the main characteristics of the syndrome which is transmitted as an autosomal dominant. Cephalometric analysis and speech and hearing evaluation of our patients confirmed the above findings.

Adolescent↗