Hartmut Engel

Mutations in the NSDHL gene, encoding a 3β-hydroxysteroid dehydrogenase, cause CHILD syndrome

We report for the first time that CHILD syndrome (MIM 308050), an X-linked dominant, male-lethal trait characterized by an inflammatory nevus with striking lateralization and strict midline demarcation, as well as ipsilateral hypoplasia of the body is caused by mutations in the gene NSDHL located at Xq28 (NAD(P)H steroid dehydrogenase-like protein) encoding a 3beta-hydroxysteroid dehydrogenase functioning in the cholesterol biosynthetic pathway. SSCA and genomic sequence analysis of NSDHL identified in 6 patients with CHILD syndrome, including one boy as well as a mother and her daughter, mutations potentially impairing protein function. This phenotype is distinct from, but shares various clinical and biochemical findings with chondrodysplasia punctata (CDPX2, MIM 302960). CDPX2 is due to mutations affecting a delta8-delta7 sterol isomerase (EBP, emopamil binding protein, at Xp11.22-p11.23) that functions downstream of NSDHL in a later step of cholesterol biosynthesis. EBP was unaffected in the patients analyzed by us demonstrating that CHILD syndrome and CDPX2 are not caused by allelic mutations. Two mouse X-linked dominant male-lethal traits, bare patches (Bpa) and striated (Str) had previously been associated with mutations in Nsdhl. They provide animal models for the study of CHILD syndrome, a further human condition due to mutations in a gene of the cholesterol synthesis pathway.

Genetic and functional linkage of Kir5.1 and Kir2.1 channel subunits

We have identified several cDNAs for the human Kir5.1 subunit of inwardly rectifying K+ channels. Alternative splicing of exon 3 and the usage of two alternative polyadenylation sites contribute to cDNA diversity. The hKir5.1 gene KCNJ16 is assigned to chromosomal region 17q23.1–24.2, and is separated by only 34 kb from the hKir2.1 gene (KCNJ2). In the brain, Kir5.1 mRNA is restricted to the evolutionary older parts of the hindbrain, midbrain and diencephalon and overlaps with Kir2.1 in the superior/inferior colliculus and the pontine region. In the kidney Kir5.1 and Kir2.1 are colocalized in the proximal tubule. When expressed in Xenopus oocytes, Kir5.1 is efficiently targeted to the cell surface and forms electrically silent channels together with Kir2.1, thus negatively controlling Kir2.1 channel activity in native cells.

Lisch corneal dystrophy is genetically distinct from Meesmann corneal dystrophy and maps to Xp22.3

PURPOSE There is an ongoing discussion whether Lisch corneal dystrophy (band-shaped and whorled microcystic dystrophy of the corneal epithelium) represents a disorder that is different from Meesmann corneal dystrophy. The purpose of this study was to evaluate at the molecular level if Lisch and Meesmann corneal dystrophies are genetically distinct. METHODS We examined at the slit lamp a total of 48 members of a family with an aggregation of Lisch corneal dystrophy. Genomic DNA was extracted from leukocytes of the peripheral blood of seven affected and six unaffected members of this family. Mutational hotspots in the cornea-specific keratin genes K3 and K12 were scanned for mutations by single-strand conformation analysis. To test for linkage to the keratin K3 or K12 loci or for X-chromosomal inheritance, six (K3) and four (K12) microsatellite markers each flanking the keratin loci as well as 22 microsatellite markers covering the X-chromosome were typed. Linkage was analyzed using the MLINK and FASTMAP procedures. RESULTS A total of 19 trait carriers were identified in six generations of the family. No hereditary transmission from father to son was observed. Linkage was excluded for the keratin K3 and K12 genes. Furthermore, single-strand conformation analysis detected no mutations in these genes. Multipoint linkage analysis revealed linkage with a maximum likelihood of the odds (LOD) score of 2.93 at Xp22.3. Linkage was excluded for Xp22.2 to Xqter. CONCLUSIONS Lisch corneal dystrophy is genetically different from Meesmann corneal dystrophy. Evidence was found for linkage of the gene for Lisch corneal dystrophy to Xp22.3.

Genes for human general transcription initiation factors TFIIIB, TFIIIB-associated proteins, TFIIIC2 and PTF/SNAPC: functional and positional candidates for tumour predisposition or inherited genetic diseases?

TFIIIB, TFIIIC2, and PTF/SNAPC are heteromultimeric general transcription factors (GTFs) needed for expression of genes encoding small cytoplasmic (scRNAs) and small nuclear RNAs (snRNAs). Their activity is stimulated by viral oncogenes, such as SV40 large T antigen and Adenovirus E1A, and is repressed by specific transcription factors (STFs) acting as anti-oncogenes, such as p53 and pRb. GTFs role as final targets of critical signal transduction pathways, that control cell proliferation and differentiation, and their involvement in gene expression regulation suggest that the genes encoding them are potential proto-oncogenes or anti-oncogenes or may be otherwise involved in the pathogenesis of inherited genetic diseases. To test our hypothesis through the positional candidate gene approach, we have determined the physical localization in the human genome of the 11 genes, encoding the subunits of these GTFs, and of three genes for proteins associated with TFIIIB (GTF3BAPs). Our data, obtained by chromosomal in situ hybridization, radiation hybrids and somatic cell hybrids analysis, demonstrate that these genes are present in the human genome as single copy sequences and that some cluster to the same cytogenetic band, alone or in combination with class II GTFs. Intriguingly, some of them are localized within chromosomal regions where recurrent, cytogenetically detectable mutations are seen in specific neoplasias, such as neuroblastoma, uterine leyomioma, mucoepidermoid carcinoma of the salivary glands and hemangiopericytoma, or where mutations causing inherited genetic diseases map, such as Peutz-Jeghers syndrome. Their molecular function and genomic position make these GTF genes interesting candidates for causal involvement in oncogenesis or in the pathogenesis of inherited genetic diseases.

The neurobeachin gene (Nbea) identifies a new region of homology between mouse central Chromosome 3 and human Chromosome 13q13

The neurobeachin gene (Nbea) identifies a new region of homology between mouse central chromosome 3 and human chromosome 13q13

Genomic localization of the human genes TAF1A, TAF1B and TAF1C, encoding TAFI48, TAFI63 and TAFI110 subunits of class I general transcription initiation factor SL1

Human SL1 is a general transcription initiation factor (GTF) essential for RNA polymerase I to start rRNA synthesis at class I promoters. It is comprised of the TATA box-binding protein (TBP) and three TBP-associated factors (TAFI48, TAFI63 and TAFI110). We have determined that the human genes TAF1A, TAF1B and TAF1C, encoding these three TAFI polypeptides, are localized at lq42, 2p25 and 16q24, respectively. All three genes are present as single copies in the human genome and map to different chromosomes, as shown by somatic cell hybrid panel and radiation hybrid panel analysis and FISH. Two of these genes, TAF1C and TAF1B, are transcribed into multiple RNAs, as determined through Northern analysis of mRNA from various human organs and cell lines. If translated into different polypeptides, this could result in production of variant isoforms of SL1 with different activation potentials.

Brief Communication: Genomics of the Human Genes Encoding Four TAFII Subunits of TFIID, the Three Subunits of TFIIA, as well as CDK8 and SURB7

By in situ chromosomal hybridization, and by somatic cell and radiation hybrid analysis, we have determined the genomic position of the human genes encoding four TAFII subunits of TFIID (TAFII150, TAFII105, TAFII68, TAFII18), the three subunits of TFIIA (TFIIA35 and TFIIA19, both encoded by the same gene, and TFIIA12), CDK8, and SURB7. All of these proteins are bona fide components of human class II holoenzymes as well as targets of signal transduction pathways that regulate genome expression. The genes encoding them are present in the human genome in a single copy and are localized at 8q23, 18q11.2, 17q11.1–11.2, 1p21, 14q31, 15q21–23, 13q12, and 12p12, respectively. We have mapped all of them to chromosomal regions where hereditary genetic diseases have been localized or which are involved in malignancies, which makes them potential candidates for a causal involvement in these phenotypes.