Mutation in fibrillin-1 and the Marfanoid-craniosynostosis (Shprintzen-Goldberg) syndrome.

Recent reports have described a distinct and recurrent pattern of systemic malformation that associates craniosynostosis and neurodevelopmental abnormalities with many clinical features of the Marfan syndrome (MFS), an autosomal dominant disorder of the extracellular microfibril caused by defects in the gene encoding fibrillin-1, FBN1 (ref. 8). Additional common findings include other craniofacial anomalies, hypotonia, obstructive apnea, foot deformity, and congenital weakness of the abdominal wall. So far, only 11 cases have been reported precluding the assignment of definitive diagnostic criteria. While it remains unclear whether these cases represent a discrete clinical entity with a single aetiology, they have been pragmatically grouped under the rubric Marfanoid-craniosynostosis or Shprintzen-Goldberg syndrome (SGS). Because of the significant clinical overlap between MFS and SGS, we proposed that they may be caused by allelic mutations. We now report two SGS patients who harbour mutations in FBN1. While it remains unclear whether these mutations are sufficient for the clinical expression of the entire SGS phenotype, these data suggest a role for fibrillin-1 in early craniofacial and central nervous system development. Our recent observation that FBN1 transcript is expressed as early as the 8-cell stage of human embryogenesis is consistent with this hypothesis.

A type X collagen mutation causes Schmid metaphyseal chondrodysplasia.

The expression of type X collagen is restricted to hypertrophic chondrocytes in regions undergoing endochondral ossification, such as growth plates. The precise function of type X collagen is unknown but the tissue-specific expression prompted us to examine the gene in hereditary disorders of cartilage and bone growth (osteochondrodysplasias). We have identified a 13 base pair deletion in one type X collagen allele segregating with autosomal dominant Schmid metaphyseal chondrodysplasia in a large Mormon kindred (lod score = 18.2 at theta = 0). The mutation produces a frameshift which alters the highly conserved C-terminal domain of the alpha 1(X) chain and reduces the length of the polypeptide by nine residues. This mutation may prevent association of the mutant polypeptide during trimer formation, resulting in a decreased amount of normal protein.

A recurrent mutation in the tyrosine kinase domain of fibroblast growth factor receptor 3 causes hypochondroplasia.

Hypochondroplasia (MIM 146000) is an autosomal dominant skeletal dysplasia with skeletal features similar to but milder than those seen in achondroplasia. Within the past year, the achondroplasia locus has been mapped to 4p 16.3 (refs 5-7) and mutations in the fibroblast growth factor receptor 3 (FGFR3) gene have been identified in patients with the disorder. More than 95% of 242 cases reported so far are accounted for by a single Gly380Arg mutation. McKusick et al. proposed that achondroplasia and hypochondroplasia are allelic based on the similarities in phenotype between the two disorders and the identification of a severely dwarfed individual whose father had achondroplasia and whose mother had hypochondroplasia. There is also genetic linkage evidence that hypochondroplasia and achondroplasia map to the same locus. We therefore began a systematic screening of FGFR3 to detect mutations in patients with hypochondroplasia. We now report a single FGFR3 mutation found in 8 out of 14 unrelated patients with hypochondroplasia. This mutation causes a C to A transversion at nucleotide 1620, resulting in an Asn540Lys substitution in the proximal tyrosine kinase domain.

The 2019-2020 volcanic eruption of Late'iki (Metis Shoal), Tonga.

Late'iki (previously known as Metis Shoal) is a highly active volcano in the Tofua arc with at least four temporary island-building eruptions and one submarine eruption in the last 55 years. The most recent eruption, commencing in October 2019, resulted in lava effusion and subsequent phreatic explosions, the construction of a short-lived island that was quickly eroded by wave action and possibly further phreatic activity that continued into January 2020. The two-pyroxene dacite from the 2019 eruption is similar to the 1967/8 eruptions suggesting the magma is residual from earlier eruptions and has not undergone further differentiation in the last 50 years. New observations of the 2019 eruption site confirm the lava-dominant character of the volcano summit but a thin veneer of wave-reworked, finely fragmented lava material remains that is interpreted to have been produced by phreatic explosions from hot rock-water interactions during the effusive eruption. A notable absence of quench-fragmented hyaloclastite breccias suggests that non-explosive quench fragmentation processes were minimal at these shallow depths or that hyaloclastite debris has resedimented to greater depths beyond our summit survey area.

A peculiar Scottish disorder.

A highly contagious behavioural affliction is now endemic in highland areas of Scotland. Pretravel advice ought to include a health warning to sport-lovers venturing north into wild, highlands of Gaeldom. It particularly affects young adults and predominates in men, although women are affected. The disorder can be acute or chronic and when severe, it can threaten one's life and limbs. Acute attacks may bring spontaneous recovery in months, but the chronic state can last for a life-time. Death will overtake some before it runs its inevitable course.

Bone dysplasias in man: molecular insights.

The recent explosion in the number of identified genes involved in the human skeletal dysplasias has dramatically advanced this particular field. While linkage efforts are mapping hereditary disorders of the skeleton at an ever accelerating pace, progress in the Human Genome Project is providing tools for rapid gene discovery after the map location is known. Emerging themes in the molecular analysis of the skeletal dysplasias include the identification of allelic series of disorders and the existence of mutational and genetic heterogeneity in many of these conditions. Allelic series include those conditions caused by mutations in the genes encoding type II collagen (COL2A1), cartilage oligomeric matrix protein (COMP), fibroblast growth factor receptor 3 (FGFR3) and the diastrophic dysplasia sulfate transporter (DTDST). The recognition of these phenomena has initiated the analysis of the relationship between disease phenotype and gene.

Glanzmann thrombasthenia. Cooperation between sequence variants in cis during splice site selection.

Glanzmann thrombasthenia (GT), an autosomal recessive bleeding disorder, results from abnormalities in the platelet fibrinogen receptor, GP(IIb)-IIIa (integrin alpha(IIb)beta3). A patient with GT was identified as homozygous for a G-->A mutation 6 bp upstream of the GP(IIIa) exon 9 splice donor site. Patient platelet GP(IIIa) transcripts lacked exon 9 despite normal DNA sequence in all of the cis-acting sequences known to regulate splice site selection. In vitro analysis of transcripts generated from mini-gene constructs demonstrated that exon skipping occurred only when the G-->A mutation was cis to a polymorphism 116 bp upstream, providing precedence that two sequence variations in the same exon which do not alter consensus splice sites and do not generate missense or nonsense mutations, can affect splice site selection. The mutant transcript resulted from utilization of a cryptic splice acceptor site and returned the open reading frame. These data support the hypothesis that pre-mRNA secondary structure and allelic sequence variants can influence splicing and provide new insight into the regulated control of RNA processing. In addition, haplotype analysis suggested that the patient has two identical copies of chromosome 17. Markers studied on three other chromosomes suggested this finding was not due to consanguinity. The restricted phenotype in this patient may provide information regarding the expression of potentially imprinted genes on chromosome 17.

Differential expression in male and female mouse liver of very similar mRNAs specified by two group 1 major urinary protein genes.

The major urinary proteins of the mouse are encoded by a large multigene family composed of several distinct groups of genes distinguished by differences in sequence and expression characteristics. The genes in the largest group (group 1) show greater than 99% pairwise similarity in their exons. By hybridization between RNA and a specifically designed oligonucleotide, we confirmed that genes of this group are expressed mainly in the liver. By using additional gene-specific oligonucleotide probes, we have been able to distinguish between the species of mRNA corresponding to two of these genes and to measure their abundance in male and female liver. Both mRNAs are present in male liver at high but different levels. Both are also present in female liver, one at a much lower level than in the male and the second at a very low level indeed. Both are present at male levels in the livers of females induced with testosterone. These results show unequivocally that the expression of different group 1 Mup genes is differentially influenced by the hormonal status of the mouse.

High throughput SNP and expression analyses of candidate genes for non-syndromic oral clefts.

BACKGROUND: Recent work suggests that multiple genes and several environmental risk factors influence risk for non-syndromic oral clefts, one of the most common birth defects in humans. Advances in high-throughput genotyping technology now make it possible to test multiple markers in many candidate genes simultaneously. METHODS: We present findings from family based association tests of single nucleotide polymorphism (SNP) markers in 64 candidate genes genotyped using the BeadArray approach in 58 case-parent trios from Maryland (USA) to illustrate how multiple markers in multiple genes can be analysed. To assess whether these genes were expressed in human craniofacial structures relevant to palate and lip development, we also analysed data from the Craniofacial and Oral Gene Expression Network (COGENE) consortium, and searched public databases for expression profiles of these genes. RESULTS: Thirteen candidate genes showed significant evidence of linkage in the presence of disequilibrium, and ten of these were found to be expressed in relevant embryonic tissues: SP100, MLPH, HDAC4, LEF1, C6orf105, CD44, ALX4, ZNF202, CRHR1, and MAPT. Three other genes showing statistical evidence (ADH1C, SCN3B, and IMP5) were not expressed in the embryonic tissues examined here. CONCLUSIONS: This approach demonstrates how statistical evidence on large numbers of SNP markers typed in case-parent trios can be combined with expression data to identify candidate genes for complex disorders. Many of the genes reported here have not been previously studied as candidates for oral clefts and warrant further investigation.

Haplotype diversity in 11 candidate genes across four populations.

Analysis of haplotypes based on multiple single-nucleotide polymorphisms (SNP) is becoming common for both candidate gene and fine-mapping studies. Before embarking on studies of haplotypes from genetically distinct populations, however, it is important to consider variation both in linkage disequilibrium (LD) and in haplotype frequencies within and across populations, as both vary. Such diversity will influence the choice of "tagging" SNPs for candidate gene or whole-genome association studies because some markers will not be polymorphic in all samples and some haplotypes will be poorly represented or completely absent. Here we analyze 11 genes, originally chosen as candidate genes for oral clefts, where multiple markers were genotyped on individuals from four populations. Estimated haplotype frequencies, measures of pairwise LD, and genetic diversity were computed for 135 European-Americans, 57 Chinese-Singaporeans, 45 Malay-Singaporeans, and 46 Indian-Singaporeans. Patterns of pairwise LD were compared across these four populations and haplotype frequencies were used to assess genetic variation. Although these populations are fairly similar in allele frequencies and overall patterns of LD, both haplotype frequencies and genetic diversity varied significantly across populations. Such haplotype diversity has implications for designing studies of association involving samples from genetically distinct populations.

Nail patella syndrome: a review of the phenotype aided by developmental biology.

Nail patella syndrome (NPS) is an autosomal dominant condition affecting the nails, skeletal system, kidneys, and eyes. Skeletal features include absent or hypoplastic patellae, patella dislocations, elbow abnormalities, talipes, and iliac horns on x ray. Kidney involvement may lead to renal failure and there is also a risk of glaucoma. There is marked inter- and intrafamilial variability. The results of a British study involving 123 NPS patients are compared with previously published studies and it is suggested that neurological and vasomotor symptoms are also part of the NPS phenotype. In addition, the first data on the incidence of glaucoma and gastrointestinal (GI) symptoms in NPS are presented. NPS is caused by loss of function mutations in the transcription factor LMX1B at 9q34. The expansion of the clinical phenotype is supported by the role of LMX1B during development.

Twenty-two novel LMX1B mutations identified in nail patella syndrome (NPS) patients.

We report twenty-two novel mutations in the gene encoding the transcription factor LMX1B, previously shown to be mutated in persons with Nail Patella Syndrome (NPS). The mutations comprised eight missense, one splice-site, three insertion/deletion and ten nonsense or frameshift mutations. A sub-set of five recurrent mutations within the homeodomain represents over one-quarter of the described NPS mutations. The type and distribution of the mutations is consistent with the hypothesis that NPS is the result of haploinsufficiency for LMX1B.

Deletion of a branch-point consensus sequence in the LMX1B gene causes exon skipping in a family with nail patella syndrome.

Nail patella syndrome (NPS) has been shown to result from loss of function mutations within the transcription factor LMX1B. In a large NPS family a 17 bp intronic deletion encompassing a consensus branchpoint sequence was observed to segregate with the NPS phenotype. RNA analysis demonstrated that deletion of the branchpoint sequence resulted in skipping of the downstream exon. A mechanism to explain this phenomenon is presented.

A case-control study of nonsyndromic oral clefts in Maryland.

PURPOSE: Isolated, nonsyndromic oral clefts cases (n = 171) and unaffected controls (n = 182) were used to identify both genetic and environmental risk factors. METHODS: Infants born in Maryland between 1992 to 1998 with an isolated, nonsyndromic oral cleft [cleft lip (CL), cleft lip and palate (CLP), or cleft palate (CP)] were recruited and exposure plus family history data were collected. Controls were unaffected infants. DNA was collected from all cases and their parents, plus controls. RESULTS: No statistically significant association was found between any of the following: maternal smoking, vitamin use, urinary tract infection, or recreational drug use in either univariate analysis or after adjusting for maternal age and education. More control mothers reported alcohol use during the critical time period of pregnancy (one month before conception through the first trimester) as compared to case mothers. There was a 10-fold increase in risk to siblings of cases as compared to siblings of controls. Markers at four candidate genes were examined: transforming growth factor alpha (TGF alpha), transforming growth factor beta 3 (TGF beta 3), MSX1, and BCL3. Only MSX1 showed significant differences in allele frequencies between CP cases and controls. MSX1 also showed significant evidence of linkage disequilibrium with a susceptibility gene controlling risk for CP. CONCLUSION: Most environmental risk factors examined here gave little evidence of association with risk to isolated, nonsyndromic oral clefts, although any alcohol consumption seemed protective. MSX1 showed evidence of linkage disequilibrium in both case-control and case-parent trio analysis.

Prenatal exclusion testing for Huntington disease using the polymerase chain reaction.

Prenatal exclusion of Huntington disease (HD) may be carried out by analysis of cosegregating DNA markers on a first-trimester chorionic villus sample. The conventional Southern blot method is time-consuming and requires microgram quantities of DNA and milligram quantities of villus tissue. The use of the polymerase chain reaction (PCR) to amplify genomic DNA by a factor of 10(7) or more makes it possible to do analyses on very small samples in a few hours and without recourse to Southern blotting or hybridization with radioactive probes. We report on a fetus at risk of HD; prenatal testing was carried out by using the PCR to amplify a polymorphic DNA sequence adjacent to the HD locus. The risk of the fetus inheriting the HD gene could not be excluded and the pregnancy was terminated. This represents an example of gene tracking by using amplification of a restriction fragment length polymorphism at some distance from the relevant mutation.

Association between homeobox-containing gene MSX1 and the occurrence of limb deficiency.

Animal studies have suggested an important role for the homeobox-containing gene MSX1 in limb, oralfacial, and cardiac malformations. In this study of 516 Caucasians with isolated birth defects registered in the Maryland Birth Defects Reporting and Information System (BDRIS), we report an association between a dinucleotide repeat polymorphism in MSX1 and isolated limb deficiency. Frequencies of rare alleles at the MSX1 locus are significantly higher among 34 infants with limb deficiency compared to 482 infants with other isolated birth defects (oral clefts, dislocation of hip, clubfoot, hypospadias, polydactyly, or syndactyly) (chi2 = 11.0, df = 3, P = 0.012). Infants carrying the rare alleles had a 4.81-fold higher risk of a limb deficiency when the mother reported smoking during pregnancy, compared to infants who are homozygous for the common allele and whose mother did not smoke. The significance of this apparent gene-environment interaction is attributed to infants with malformation of the lower limb. The statistical association and potential gene-environment interaction observed in this study (which was originally designed to investigate oral clefts) are compatible with results from animal studies involving the MSX1 gene, and suggests that further investigation into biological mechanisms is warranted.

Application of transmission disequilibrium tests to nonsyndromic oral clefts: including candidate genes and environmental exposures in the models.

Extensive epidemiological and genetic studies of the cause of oral clefts have demonstrated strong familial aggregation but have failed to yield definitive evidence of any single genetic mechanism. We used the transmission/disequilibrium test (TDT) to investigate the relationship between oral clefts and markers associated with five candidate genes by utilizing 160 parent-offspring trios. Conditional logistic regression models extended the TDT to include covariates as effect modifiers, thus permitting tests for gene-environment interactions. For four of these candidates [transforming growth factor alpha (TGFA), transforming growth factor beta 3 (TGFB3), retinoic acid receptor (RARA), and the proto-oncogene BCL3], we detected modestly elevated odds ratios for the transmission of one marker allele to cleft probands when all the trios were analyzed together. These odds ratios increased when information on type of cleft, race, family history, or maternal smoking were incorporated as effect modifiers. We detected significant interaction between maternal smoking and the transmission of alleles for markers near TGFA and TGFB3; excess transmission of allele 3 at BCL3 was most significant among cleft lip probands; and the odds ratios for transmission of alleles at D19S178 and THRA1 were significant when ethnic group was included in the model. We suggest that utilizing an analytical strategy that allows for stratification of data and incorporating environmental effects into a single analysis may be more effective for detecting genes of small effect.

Delayed membranous ossification of the cranium associated with familial translocation (2;3)(p15;q12).

The relationship of delayed membranous cranial ossification to cranium bifidum and parietal foramina syndromes is unclear. We report on a family with delayed cranial membranous ossification (OMIM 155980) that segregates with an apparently balanced reciprocal translocation between chromosomes 2 and 3. The propositus had apparently low-set ears, proptosis, and a soft skull at birth. A radiographic survey of the skeleton showed markedly decreased ossification of the cranial bones and no other skeletal abnormalities. The mother and maternal grandmother of the propositus have brachycephaly, hypertelorism, and a history of a soft skull at birth. Chromosome analysis of peripheral blood from the propositus showed 46,XY,t(2;3)(p15;q12). The propositus, mother, and grandmother carry the same reciprocal translocation, whereas the mother's two phenotypically normal sibs have a normal karyotype. We used an STS-linked BAC resource to define the translocation breakpoint by identifying flanking BAC clones from both chromosomes 2, 1006D24 (D2S2279) and 1060A5 (D2S2231), and chromosome 3, 3D17 (WI8558) and 3D18 [CITB Human BAC Library, J.R.K.]. This represents the second report of a family with delayed membranous ossification of the cranium and the first report of the phenotype segregating with a chromosome rearrangement.