CHILD syndrome: the NSDHL gene and its role in CHILD syndrome, a rare hereditary disorder.

BACKGROUND: CHILD syndrome, a rare hereditary disorder of keratinization (MIM 308050, 300275), is the acronym proposed by Happle to name a rare entity, characterized by congenital hemidysplasia, icthyosiform nevus and limb defects, ranging from digital hypoplasia to icthyosiform nevus and ipsilateral limb defects, ranging from digital hypoplasia to complete amelia. PATIENTS AND METHODS: A 9-month-old female infant presented with skin and limb defects involving the right side of her body. Clinical and laboratory evaluation was performed, including DNA sequence analysis of the NSDHL gene. RESULTS: Our patient presented with some of the typical clinical characteristics of CHILD syndrome, i.e. two large erythematous plaques with sharp borders, covered with yellow, wax-like scaling, on the right axilla and on the right groin, dysplastic right hand and alopecia of the right occipital area. The diagnosis was confirmed by DNA screening analysis, that detected a missense mutation c.314C-->T;p-A105V, in the coding region of the NSDHL gene (exon4) of our patient. CONCLUSIONS: This is the first report of CHILD syndrome ever reported in Greece. We suggest that the diagnosis of the syndrome is important for patient information and genetic counselling.

Synpolydactyly: clinical and molecular advances.

Synpolydactyly (SPD) is a rare limb deformity showing a distinctive combination of syndactyly and polydactyly. Of the nine non-syndromic syndactylies, it is clinically and genetically one of the most heterogeneous malformation. SPD families may show clinical features consistent with the Temtamy and McKusick criteria as well as additional phenotypic variants, which vary from case to case. In certain instances, these variants predominate in a given family, while the typical SPD features remain less explicit. We have reviewed all the clinical variants occurring in well-documented SPD families. We conclude that typical SPD features can be delineated from minor clinical variants. Then, we propose to lump all the phenotypic variants, manifesting themselves in SPD families into three categories: (i) typical SPD features, (ii) minor variants, and (iii) unusual phenotypes. Next, we discuss the likely reasons for the occurrence of minor variants and the obvious lack of penetrance in SPD families. Finally, we show that for the SPD phenotype associated with HOXD13 mutations, a straightforward genotype-phenotype correlation is weak. Our lumping and splitting scheme for SPD phenotypic variants could be useful for the understanding of this interesting malformation.

Novel interaction partners of Bardet-Biedl syndrome proteins.

Bardet-Biedl syndrome (BBS) is a rare, developmental disorder characterized by six major symptoms: rod-cone dystrophy, obesity, polydactyly, renal abnormalities, learning difficulties, and hypogonadism. Secondary features include cardiac and hepatic anomalies, metabolic disturbancies, and hearing loss. BBS is genetically heterogeneous with 12 disease genes (BBS1-BBS12) described thus far. Current data suggest a functional disturbance in ciliary function and intraflagellar transport being associated with the phenotype. However, the precise functions of the BBS proteins have yet to be elucidated. This study focuses on the detection of protein factors interacting with BBS proteins. Applying yeast two-hybrid (Y2H) technology we found a series of novel, functionally potentially plausible binding partners of BBS1, BBS2, BBS4, and BBS7. Protein interactions were supported by coimmunoprecipitation analyses (ALDOB, EPAS1) and substantiated by colocalization studies at the subcellular level (ALDOB, EXOC7, FLOT1, KRT18, PAX2). Our work provides new insights into the understanding of BBS interactions and thus their biological function.

Genetic heterogeneity of synpolydactyly: a novel locus SPD3 maps to chromosome 14q11.2-q12.

Syndactyly type II or synpolydactyly (SPD) is the second most frequent syndactyly type and is inherited in an autosomal dominant fashion. The cardinal features of this malformation are the cutaneous or bony fusion of third and fourth fingers, and fourth and fifth toes associated with additional digital elements within the web. It shows incomplete penetrance and high inter- and intrafamilial phenotypic variability. Two loci are known for SPD (MIM 186000, MIM 608180) associated with mutations in HOXD13 and FBLN1, respectively. Here, we report further genetic heterogeneity for SDP. Employing a whole genomic screen, we demonstrate, in a large Pakistani kindred, that the classical phenotype of SPD maps on a new locus at chromosome 14q11.2-q12. The highest LOD score (Z(max) = 4.06) was obtained with microsatellite marker D14S264, and the multipoint LOD score reached a maximum of 5.01. Haplotype analysis revealed that the disease interval is flanked by microsatellite markers D14S283 and D14S1060, encompassing a physical distance of 10.72 Mb. We propose to allocate to this locus the symbol SPD3 (synpolydactyly 3), and to name the loci associated with HOXD13 or FBLN1 mutations SPD1 and SPD2, respectively.

A simple method for characterising syndactyly in clinical practice.

Non-syndromic syndactyly is a heterogeneous group of limb malformations involving webbing of fingers and/or toes. There are at least nine non-syndromic types described in the literature. For the clinician and the genetic counsellor not having gathered experience with this malformation, it is rather tedious to identify the correct subtype for the patient's phenotype. We therefore present a protocol for clinical use, which visualises the malformation in a graphical way and thereby simplifies typing. In addition, this protocol provides a simple documentation system for reporting clinical data for new syndactyly families. It might encourage clinicians to report families that are still unclassifed and thus, helping to extend and improve the existing classification system.

CHILD syndrome caused by a deletion of exons 6-8 of the NSDHL gene.

The X-linked dominant CHILD syndrome (congenital hemidysplasia with ichthyosiform nevus and limb defects) is a rare developmental defect characterized by a strictly lateralized inflammatory nevus. In the majority of cases, the right side of the body is affected. Ipsilateral hypoplastic lesions may involve the brain, skeletal structures, lungs, heart or kidneys. We describe a case of CHILD syndrome involving the left side of the body. Absence of metacarpal, metatarsal and phalangeal bones of the left hand and foot resulted in oligodactyly, with only 3 fingers and 1 toe. An ipsilateral inflammatory epidermal nevus with hyperkeratosis, parakeratosis, acanthosis and perivascular lymphohistiocytic infiltrate was strictly confined to the left half of the patient's body. The phenotype was shown to be associated with a deletion of exons 6-8 of the X-linked NSDHL gene, confirming that CHILD syndrome is due to loss of function of an enzyme involved in cholesterol biosynthesis.

Variable phenotype in Greig cephalopolysyndactyly syndrome: clinical and radiological findings in 4 independent families and 3 sporadic cases with identified GLI3 mutations.

Greig cephalopolysyndactyly (GCPS) (OMIM 175700) is an autosomal dominant disorder characterized by a distinct combination of craniofacial, hand and foot malformations. In this report, clinical and radiological findings of 12 patients with GCPS derived from 4 independent families and 3 sporadic cases with documented GLI3 mutations are presented with particular emphasis on inter- and intrafamilial variability. In a particularly instructive family in which 9 members of 4 generations could be studied clinically and molecularly, a missense mutation (R625W) is transmitted and shows a partially penetrant pattern. In a branch of the family, the GCPS phenotype skips a generation via a normal female carrier without clinical signs providing evidence that GCPS does not always manifest full penetrance as generally supposed.

Selective Differential Display of RNAs containing interspersed repeats: analysis of changes in the transcription of HERV-K LTRs in germ cell tumors.

A technique for the Selective Differential Display of RNAs containing Interspersed Repeats (SDDIR) has been elaborated. SDDIR involves two main steps: (1) selective amplification by RT-PCR of a subset of the total cellular RNA containing a certain type of repetitive element, and (2) side-by-side display of the amplicons derived from the tissues under comparison by means of gel electrophoresis in parallel lanes. The technique was used to compare the expression of transcripts containing LTR (Long Terminal Repeat) sequences derived from human endogenous retrovirus K (HERV-K) in testicular germ cell tumors and in corresponding normal tissue. SDDIR enabled us to obtain an overview of LTRs represented in the total transcribed fraction and to reveal differences in transcription patterns of the LTRs in normal and tumor tissues. An unexpectedly large number of LTRs was found to be transcribed, and the levels of many of the transcripts differed between normal and tumor tissues.

Expression pattern in brain of TASK-1, TASK-3, and a tandem pore domain K(+) channel subunit, TASK-5, associated with the central auditory nervous system.

TWIK-related acid-sensitive K(+) (TASK) channels contribute to setting the resting potential of mammalian neurons and have recently been defined as molecular targets for extracellular protons and volatile anesthetics. We have isolated a novel member of this subfamily, hTASK-5, from a human genomic library and mapped it to chromosomal region 20q12-20q13. hTASK-5 did not functionally express in Xenopus oocytes, whereas chimeric TASK-5/TASK-3 constructs containing the region between M1 and M3 of TASK-3 produced K(+) selective currents. To better correlate TASK subunits with native K(+) currents in neurons the precise cellular distribution of all TASK family members was elucidated in rat brain. A comprehensive in situ hybridization analysis revealed that both TASK-1 and TASK-3 transcripts are most strongly expressed in many neurons likely to be cholinergic, serotonergic, or noradrenergic. In contrast, TASK-5 expression is found in olfactory bulb mitral cells and Purkinje cells, but predominantly associated with the central auditory pathway. Thus, TASK-5 K(+) channels, possibly in conjunction with auxiliary proteins, may play a role in the transmission of temporal information in the auditory system.

Identification of paralogous HERV-K LTRs on human chromosomes 3, 4, 7 and 11 in regions containing clusters of olfactory receptor genes.

A locus harboring a human endogenous retroviral LTR (long terminal repeat) was mapped on the short arm of human chromosome 7 (7p22), and its evolutionary history was investigated. Sequences of two human genome fragments that were homologous to the LTR-flanking sequences were found in human genome databases: (1) an LTR-containing DNA fragment from region 3p13 of the human genome, which includes clusters of olfactory receptor genes and pseudogenes; and (2) a fragment of region 21q22.1 lacking LTR sequences. PCR analysis demonstrated that LTRs with highly homologous flanking sequences could be found in the genomes of human, chimp, gorilla, and orangutan, but were absent from the genomes of gibbon and New World monkeys. A PCR assay with a primer set corresponding to the sequence from human Chr 3 allowed us to detect LTR-containing paralogous sequences on human chromosomes 3, 4, 7, and 11. The divergence times for the LTR-flanking sequences on chromosomes 3 and 7, and the paralogous sequence on chromosome 21, were evaluated and used to reconstruct the order of duplication events and retroviral insertions. (1) An initial duplication event that occurred 14-17 Mya and before LTR insertion - produced two loci, one corresponding to that located on Chr 21, while the second was the ancestor of the loci on chromosomes 3 and 7. (2) Insertion of the LTR (most probably as a provirus) into this ancestral locus took place 13 Mya. (3) Duplication of the LTR-containing ancestral locus occurred 11 Mya, forming the paralogous modern loci on Chr 3 and 7.

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.

Systematic screening for mutations in the human necdin gene (NDN): identification of two naturally occurring polymorphisms and association analysis in body weight regulation.

BACKGROUND: NDN, which codes for the human necdin protein, is a candidate gene for Prader-Willi syndrome (PWS). One feature of this neurogenetic disorder is hyperphagia resulting in extreme obesity observed later in development. OBJECTIVE AND DESIGN: In this study we have used single-strand conformation polymorphism (SSCP) analysis to identify sequence variants at the human necdin gene. Furthermore we tested whether these variants were associated with obesity in extremely obese German children and adolescents. RESULTS: Two gene variants could be identified: a g.1352T-->C polymorphism in the putative promotor region and a silent g.2311C-->T polymorphism in the coding region. Genotype and allele frequency distribution of both of the polymorphisms were not significantly different between lower and higher body mass index (BMI) subjects. CONCLUSIONS: Hence, it is unlikely that these polymorphisms play a major role in the emergence of juvenile onset human obesity.

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.

THIK-1 and THIK-2, a novel subfamily of tandem pore domain K+ channels.

Two cDNAs encoding novel K(+) channels, THIK-1 and THIK-2 (tandem pore domain halothane inhibited K(+) channel), were isolated from rat brain. The proteins of 405 and 430 amino acids were 58% identical to each other. Homology analysis showed that the novel channels form a separate subfamily among tandem pore domain K(+) channels. The genes of the human orthologs were identified as human genomic data base entries. They possess one intron each and were assigned to chromosomal region 14q24.1-14q24.3 (human (h) THIK-1) and 2p22-2p21 (hTHIK-2). In rat (r), THIK-1 (rTHIK-1) is expressed ubiquitously; rTHIK-2 expression was found in several tissues including brain and kidney. In situ hybridization of brain slices showed that rTHIK-2 is strongly expressed in most brain regions, whereas rTHIK-1 expression is more restricted. Heterologous expression of rTHIK-1 in Xenopus oocytes revealed a K(+) channel displaying weak inward rectification in symmetrical K(+) solution. The current was enhanced by arachidonic acid and inhibited by halothane. rTHIK-2 did not functionally express. Confocal microscopy of oocytes injected with green fluorescent protein-tagged rTHIK-1 or rTHIK-2 showed that both channel subunits are targeted to the outer membrane. However, coinjection of rTHIK-2 did not affect the currents induced by rTHIK-1, indicating that the two channel subunits do not form heteromers.