Congenital heart defects and genetic variants in the methylenetetrahydroflate reductase gene.

BACKGROUND: Most non-syndromic congenital heart defects (CHD) are caused by a complex interaction between maternal lifestyle factors, environmental exposures, and maternal and fetal genetic variants. Maternal periconceptional intake of folic acid containing vitamin supplements is reported to decrease the risk of CHD. The 677C-->T and 1298A-->C polymorphisms in the methylenetetrahydrofolate reductase (MTHFR) gene decrease enzyme activity. OBJECTIVE: To examine the relation between CHD and maternal and fetal MTHFR polymorphisms. METHODS: 375 nuclear families were studied. The transmission/disequilibrium test was used to test for transmission distortion in complete triads. A log-linear approach was used to test for associations between CHD and maternal and offspring polymorphisms, and to estimate independently the contributions of maternal and fetal variants to relative risks. Haplotype frequencies were estimated and a haplotype transmission disequilibrium test carried out. RESULTS: The 1298C allele was transmitted less often than expected (p = 0.0013). There was no distortion in the transmission of the 677T allele, neither was there evidence of a parent of origin effect in the transmission of either of the single nucleotide polymorphisms. The 677C-1298C haplotype was also transmitted less often than expected (p = 0.0020). The relative risk associated with inheriting one copy of the 1298C allele was 0.64 (95% confidence interval, 0.48 to 0.87) and the that associated with inheriting two copies of the 1298C allele, 0.38 (0.21 to 0.70). CONCLUSIONS: The apparent protective effect of the MTHFR 1298C allele against CHD could have several explanations and further study is needed.

Adrenal insufficiency and hypertension in a newborn infant with Smith-Lemli-Opitz syndrome.

Smith-Lemli-Opitz syndrome (SLOS) is an autosomal recessive disorder caused by mutations in the 7-dehydrocholesterol reductase gene, DHCR7. The diagnosis is based on the biochemical findings of elevated plasma 7-dehydrocholesterol (7DHC) levels. Adrenal insufficiency with hyponatremia has been reported in 3 patients with severe SLOS; in those cases it was thought to be caused by aldosterone deficiency because it responded to mineralocorticoid replacement. We present a fourth patient with a severe form of SLOS and adrenal insufficiency who had unexplained persistent hypertension, a combination of signs that has not been reported previously in SLOS.

Smith-Lemli-Opitz (RHS) syndrome: holoprosencephaly and homozygous IVS8-1G-->C genotype.

Smith-Lemli-Opitz syndrome (RHS) (SLOS, OMIM 270400) is an autosomal recessive disorder of cholesterol biosynthesis caused by mutations of the 3beta-hydroxysterol Delta(7)-Delta(8)-reductase gene, DHCR7. We report a fetus with holoprosencephaly and multiple congenital anomalies who was homozygous for the IVS8-1G-->C mutation. Following termination of pregnancy, both the elevated amniotic fluid 7-dehydrocholesterol level and the DHCR7 mutations were demonstrated. Two other newborn infants with IVS8-1G-->C/IVS8-1G-->C genotype are described. This report illustrates a severe phenotypic extreme of SLOS associated with a null genotype, underscores the complex relationship between SLOS and holoprosencephaly, and discusses the possible pathogenetic mechanisms of the development of holoprosencephaly in SLOS.

Biochemical, phenotypic and neurophysiological characterization of a genetic mouse model of RSH/Smith--Lemli--Opitz syndrome.

The RSH/Smith--Lemli--Opitz syndrome (RSH/SLOS) is a human autosomal recessive syndrome characterized by multiple malformations, a distinct behavioral phenotype with autistic features and mental retardation. RSH/SLOS is due to an inborn error of cholesterol biosynthesis caused by mutation of the 3 beta-hydroxysterol Delta(7)-reductase gene. To further our understanding of the developmental and neurological processes that underlie the pathophysiology of this disorder, we have developed a mouse model of RSH/SLOS by disruption of the 3 beta-hydroxysterol Delta(7)-reductase gene. Here we provide the biochemical, phenotypic and neurophysiological characterization of this genetic mouse model. As in human patients, the RSH/SLOS mouse has a marked reduction of serum and tissue cholesterol levels and a marked increase of serum and tissue 7-dehydrocholesterol levels. Phenotypic similarities between this mouse model and the human syndrome include intra-uterine growth retardation, variable craniofacial anomalies including cleft palate, poor feeding with an uncoordinated suck, hypotonia and decreased movement. Neurophysiological studies showed that although the response of frontal cortex neurons to the neurotransmitter gamma-amino-n-butyric acid was normal, the response of these same neurons to glutamate was significantly impaired. This finding provides insight into potential mechanisms underlying the neurological dysfunction seen in this human mental retardation syndrome and suggests that this mouse model will allow the testing of potential therapeutic interventions.

Mutation analysis and description of sixteen RSH/Smith-Lemli-Opitz syndrome patients: polymerase chain reaction-based assays to simplify genotyping.

We report the clinical and molecular data of 16 patients with RSH/Smith-Lemli-Opitz syndrome (RSH/SLOS) with varying phenotypic severity, for which we have identified mutations in both alleles. RSH/SLOS is an autosomal recessive malformation syndrome caused by mutations in the gene encoding the sterol Delta(7)-reductase. This protein catalyzes the reduction of 7-dehydrocholesterol to cholesterol in the last step of cholesterol biosynthesis via the Kandutsch-Russell pathway. In addition to previously reported mutations (T93M, L109P, G147D, W151X, T154M, R242C, A247V, T289I, IVS8-1G-->C, Y408H, and E448K), we have identified six previously undescribed mutations (321G-->C, W177R, R242H, Y318N, L341P, and C444Y). We also report rapid polymerase chain reaction (PCR)-based assays developed to detect four of the recurring mutations (T93M, W151X, V326L, and R404C) and six other RSH/SLOS mutations (321G-->C, L109P, T154M, T289I, Y318N, and L341P). The purpose of this article is to correlate detailed clinical information with molecular data in order to improve our understanding of the genotype-phenotype correlation of RSH/SLOS and to report the development of PCR-based assays that will allow more rapid mutation analysis.

Clinical analysis of a variant of Freeman-Sheldon syndrome (DA2B).

We describe the clinical characteristics of a provisionally unique form of distal arthrogryposis. The anomalies observed in affected individuals are more severe than those in distal arthrogryposis type 1 and are similar to but less dramatic than those described in distal arthrogryposis type 2A (Freeman-Sheldon syndrome). Consequently, we label this disorder distal arthrogryposis type 2B (DA2B). Affected individuals have vertical talus, ulnar deviation, severe camptodactyly, and a distinctive face characterized by a triangular shape, prominent nasolabial folds, downslanting palpebral fissures, small mouth, and a prominent chin. A gene for DA2B maps to chromosome 11p15.5. We suggest that DA2B is partly responsible for the clinical variability observed in Freeman-Sheldon syndrome.

Mutations in human TBX3 alter limb, apocrine and genital development in ulnar-mammary syndrome.

Ulnar-mammary syndrome is a rare pleiotropic disorder affecting limb, apocrine gland, tooth and genital development. We demonstrate that mutations in human TBX3, a member of the T-box gene family, cause ulnar-mammary syndrome in two families. Each mutation (a single nucleotide deletion and a splice-site mutation) is predicted to cause haploinsufficiency of TBX3, implying that critical levels of this transcription factor are required for morphogenesis of several organs. Limb abnormalities of ulnar-mammary syndrome involve posterior elements. Mutations in TBX5, a related and linked gene, cause anterior limb abnormalities in Holt-Oram syndrome. We suggest that during the evolution of TBX3 and TBX5 from a common ancestral gene, each has acquired specific yet complementary roles in patterning the mammalian upper limb.

Nonendodontic coronal resection of fused and geminated vital teeth. A new technique.

A new technique has been devised to resect vital malformed large dental crowns stemming from developmental fusion and gemination. In two cases from separate patients, resection of the fused crown with sharp osteotomes resulted in exposed pulp chambers that were subsequently allowed to heal. Root canal treatment was not necessary. Case follow-up at 12 and 4 years after orthodontics showed pulp vitality. A review of the literature as well as an explanation for healing modality were included.

A variant of Freeman-Sheldon syndrome maps to 11p15.5-pter.

Distal arthrogryposis type 1 (DA1) and Freeman-Sheldon syndrome (FSS) are the two most common known causes of inherited multiple congenital contractures. We recently have characterized a new disorder (DA2B) with a phenotype intermediate between DA1 and FSS. We report the mapping of a gene that causes DA2B to chromosome 11p15.5-pter. Linkage analysis in a single kindred generated a positive LOD score of 5.31 at theta = 0 with the marker D11S922, and recombinants localize the gene to an approximately 3.5-6.5-cM region between the marker TH and the telomere. Analysis of additional families improves the LOD score to 6.45 at theta = 0 and suggests linkage homogeneity for DA2B.

A gene for ulnar-mammary syndrome maps to 12q23-q24.1.

Ulnar-mammary syndrome (UMS) is an autosomal dominant disorder characterized by posterior limb deficiencies or duplications, apocrine/mammary gland hypoplasia and/or dysfunction, abnormal dentition, delayed puberty and genital anomalies. We report the mapping of a gene causing UMS to chromosome 12q23-24.1. Linkage analysis generated a positive lod score of 6.21 at theta = 0.00 with the marker D12S79, and recombinants bracket the UMS gene to a 21 cM region. This region contains a locus for Holt-Oram syndrome (HOS) suggesting that the genes for UMS and HOS may be allelic or closely linked. The identification of the gene causing UMS will be an important step toward understanding the molecular mechanisms that control limb and apocrine gland development.

Origins and affinities of modern humans: a comparison of mitochondrial and nuclear genetic data.

To test hypotheses about the origin of modern humans, we analyzed mtDNA sequences, 30 nuclear restriction-site polymorphisms (RSPs), and 30 tetranucleotide short tandem repeat (STR) polymorphisms in 243 Africans, Asians, and Europeans. An evolutionary tree based on mtDNA displays deep African branches, indicating greater genetic diversity for African populations. This finding, which is consistent with previous mtDNA analyses, has been interpreted as evidence for an African origin of modern humans. Both sets of nuclear polymorphisms, as well as a third set of trinucleotide polymorphisms, are highly consistent with one another but fail to show deep branches for African populations. These results, which represent the first direct comparison of mtDNA and nuclear genetic data in major continental populations, undermine the genetic evidence for an African origin of modern humans.

A gene for distal arthrogryposis type I maps to the pericentromeric region of chromosome 9.

Club foot is one of the most common human congenital malformations. Distal arthrogryposis type I (DA-1) is a frequent cause of dominantly inherited club foot. Performing a genomewide search using short tandem repeat (STR) polymorphisms, we have mapped a DA-1 gene to the pericentromeric region of chromosome 9 in a large kindred. Linkage analysis has generated a positive lod score of 5.90 at theta = 0, with the marker GS-4. Multiple recombinants bracketing the region have been identified. Analysis of an additional family demonstrated no linkage to the same locus, indicating likely locus heterogeneity. Of the autosomal congenital contracture disorders causing positional foot deformities, this is the first to be mapped.

A social-learning approach to student marijuana use.

Three hundred seventy-two college students were administered a battery of questionnaires designed to assess the predictive power of four social variables (social support, perceived sanctions, availability, family models), and six psychological ones (locus of control, mortality-conscience guilt, personal meanings, functions for continuing use, belief in consequences, societal and non-societal means of valued goal attainment) with respect to marijuana use. Results support a social learning theory interpretation of marijuana use. Users have had pleasant experiences, believe that sanctions are minimal, and that marijuana is not harmful. Six predictor variables correlated +.76 with use.