Mary Beth Dinulos

The DAZ gene cluster on the human Y chromosome arose from an autosomal gene that was transposed, repeatedly amplified and pruned

It is widely believed that most or all Y–chromosomal genes were once shared with the X chromosome. The DAZ gene is a candidate for the human Y–chromosomal Azoospermia Factor (AZF). We report multiple copies of DAZ (>99% identical in DNA sequence) clustered in the AZF region and a functional DAZ homologue (DAZH) on human chromosome 3. The entire gene family appears to be expressed in germ cells. Sequence analysis indicates that the Y–chromosomal DAZ cluster arose during primate evolution by (i) transposing the autosomal gene to the Y, (ii) amplifying and pruning exons within the transposed gene and (iii) amplifying the modified gene. These results challenge prevailing views of sex chromosome evolution, suggesting that acquisition of autosomal fertility genes is an important process in Y chromosome evolution.

Structure and chromosomal localization of the β2 subunit of the human brain sodium channel

THE β2 subunit of rat brain voltage-gated sodium channels modulates their cell-surface expression and gating. It is a 33 kDa glycoprotein with a single transmembrane segment and an immunoglobulin-like fold resembling those of cell adhesion molecules in the extracellular domain. Here we report the cDNA sequence and genomic localization of the gene encoding the human β2 subunit. The mature human β2 protein has 89% amino acid sequence identity to rat β2 and has four conserved consensus sites for N-linked glycosylation. The extra-cellular cysteine residues which are predicted to form the disulfide linkage in the immunoglobulin-like fold are also conserved, indicating that the overall structure is preserved between these two species. Using fluorescent in situ hybridization (FISH), we localized the β2 gene to human chromosome 11q3. Mutations in this region of chromosome 11 in Charcot-Marie-Tooth syndrome type 4B and in other neurological diseases cause abnormal myelination and neurological deficits. The similarity of β2 to cell adhesion molecules, including myelin protein p0, and its chromosomal location at 11q23 suggest a potential role in these demyelinating diseases.

Autosomal dominant inheritance of Barber-Say syndrome.

We report on a mother-to-son transmission of the Barber-Say syndrome, a finding that strongly supports dominant inheritance of this rare disorder. The characteristic facial changes, small ears, hirsutism, and redundant skin of our patients are consistent with the findings of five reported cases. The mother also had cleft palate and mild conductive hearing loss. Her son had a shawl scrotum, primary hypospadias, and mild hearing loss by report. The inheritance of this rare disorder has not been established. The parent-to-child transmission in this family suggests X-linked or autosomal dominant inheritance. The parents of the patient reported by Santana et al. [1993: Am. J. Med. Genet. 47:20-23] were consanguineous, suggesting autosomal recessive inheritance in other cases.

Mapping of the murine tbl1 gene reveals a new rearrangement between mouse and human X chromosomes

Several distinct regions of conservation have been found by comparative mapping of the human and mouse X Chromosomes (Chrs; Blair et al. 1994). These regions are remnants of the rearrangements that have shaped chromosomes during evolution. While seemingly few rearrangements can explain the different order of genes on the X Chr between the two species, one region corresponding to the distal end of the short arm of the human X Chr stands out as being highly rearranged in mouse (Dinulos et al. 1996; Blaschke and Rappold 1997). Indeed, at least two genes located in the pseudoautosomal region of the human X Chr are autosomal in the mouse (Disteche et al. 1992; Milatovich et al. 1993). For some genes located in human chromosomal band Xp22.3, no mouse homolog has been found, suggesting that there may have been deletion of some genes in the mouse (Ballabio and Andria 1992). In addition, CLC4 (chloride channel 4), a gene also in human chromosomal band Xp22.3, was mapped by us and by others to the X Chr in some species of mice ( M. spretus) but to an autosome in other species, including the laboratory strains of mice (Rugarli et al. 1995; Palmer et al. 1995). Both APXL (apical proteinXenopus laevis -like) and OA1 (ocular albinism type 1) are located distal to, but very near CLC4, MID1 (midline 1), and AMELX (amelogenin) in human chromosomal band Xp22.3. In contrast, the mouse homolog Apxl and Oa1 are located at band F2-3 of the mouse X Chr near Alas-2 (aminolevulinic acid synthase-2) and quite proximal to Mid-1, a gene that spans the mouse pseudoautosomal boundary, and to Clc4 andAmellocated at band F4 (Chapman et al. 1991; Dinulos et al. 1996; Newton et al. 1996; Palmer et al. 1997; Blair et al. 1998). We have recently isolated a novel gene, TBL1 (tramsducim beta-like 1), from human chromosomal band Xp22.3, which encodes a putative protein of 526 amino acids with significant homology to WD-40 repeat containing proteins (Bassi et al., manuscript in preparation). TBL1 is telomeric to the OA1 gene, but is transcribed in the opposite orientation. In human, the genomic distance between the 3 8 end of the TBL1 gene and the 3 8 end of the OA1 gene is 5.7 kb (Bassi et al., manuscript in preparation). To further examine the position of mouse homologs of genes located at human chromosomal band Xp22.3, we mapped Tbl1 to a laboratory strain of mouse (C57BL/6J) and to M. spretus,using fluorescence in situ hybridization (FISH) for physical mapping and interspecific mouse backcrosses for recombination mapping. A 10-kb genomic clone containing the last 9 exons of the mouseTbl1gene was labeled with biotin-dATP by nick translation for FISH analysis. Hybridization of the labeled probe to metaphase cells prepared from spleen cultures of male mice was carried out as previously described (Edelhoff et al. 1994). Hybridization signals were detected with a fluorescein-labeled antibody. Chromosomes were banded for identification by staining with Hoechst 33258 and actinomycin D together with propidium iodide counterstaining. In the laboratory strain C57BL/6J, 56 cells were examined yielding signals on both chromatids of the X Chr at region B-C in 30 cells (54%; Fig. 1). Similarly, inM. spretus,of 54 cells examined, 22 (41%) showed signals on both chromatids of the X Chr, also at region B-C. There was no significant hybridization to other chromosomes in either mouse species. Recombinational analysis of the Tbl1 locus was performed by Southern blotting withEcoR1-digested DNA from progeny of an interspecies backcross (C57BL/6 × M. spretus) F1 × C57BL/6 that had been previously typed for over 70 loci, including 28 genes and 40 microsatellite markers over the full length of the X Chr. These include 29 evenly spaced anchor loci that have been typed for all 230 male progeny. We used as probe a Tbl1 retina cDNA probe corresponding to nucleotide position 1617–2419 of the human TBL1 cDNA. Sequence identity within coding exons between the mouse and human cDNAs was found to be 86%. The bl1 probe hybridized to an 8.2-kbEcoR1 fragment from C57BL/6 and a 5.2-kbEcoR1 fragment fromM. spretus.As shown in Fig. 2,Tbl1 maps fromCf8 (factor VIII) and Dmd (Duchenne muscular dystrophy) in a 2-map-unit interval. There were no recombinants betweenTbl1, DXMit44, 60,or 111.The map presents the distance of each locus from the centromere, as defined by recombinants in the cross. The map location of Tbl1 lies at the distal end of a region of homology with human chromosomal band Xp28, and just proximal to a region of homology with human chromosomal band Xp21.3– 21.2 The locusApxl has also been typed in this backcross and it lies at position 66.5, more than 30 map units distal to Tbl1. Our results indicate the presence of a previously unrecognized rearrangement between human and mouse X Chrs that involves the distal end of the short arm of the human X Chr. Indeed, in the human, TBL1, OA1, and APXL are located very close to each other in chromosomal band Xp22.3, spanning a genomic region of approximately 400 kb. Mapping of their mouse homologs revealed two novel rearrangements, with Oa1 andApxl still close to each other in chromosomal bands F2-3 (Dinulos et al., 1997), but Tbl1 located much more proximal in chromosomal bands B-C, as described in the present study. Comparative maps outlining the known blocks of conservation between mouse and human X Chr are presented in Fig. 3. Comparative mapping between metatherian (marsupials), prototherian (monotremes), and eutherian mammals has shown that most of the short arm of the human X Chr is of recent addition to an ancestral X Chr (Graves 1995). Because genes located on the short arm of the human X Chr are on different autosomes in metatherian and prototherian mammals, it is likely that there have been several additions (Graves 1995). Furthermore, the boundary of the pseudoautosomal region is subject to changes between species (Ellis and Goodfellow 1989). Such complex rearrangements are likely to have shaped band Xp22.3 of the human X Chr. The Correspondence to: C.M. Disteche Mammalian Genome 9, 1062–1064 (1998).

Improving genetic health care: A Northern New England pilot project addressing the genetic evaluation of the child with developmental delays or intellectual disability

In 2006, all clinical genetics practices in Northern New England (Vermont, New Hampshire, and Maine) formed a learning collaborative with the purpose of improving genetic health care and outcomes. This article describes the current status of this effort. The methodology is based on our own modifications of the Institute of Healthcare Improvement “Breakthrough Series” and the Northern New England Cystic Fibrosis Consortium. Because of similarities across practices and the availability of existing published practice parameters, the clinical genetics evaluation of the child with developmental delay or intellectual disability was chosen as the topic to be studied. The aim was to improve the rate of etiological diagnosis of those with developmental delays referred to each genetics center by improving the processes of care. Process and outcomes were evaluated. Four of five sites also evaluated the impact of array comparative genomic hybridization (a‐CGH) laboratory testing of such patients. There was significant site‐to‐site variation in the rate of new diagnoses by a‐CGH with the average new diagnosis rate of 11.8% (range 5.4–28.8%). Barriers to implementation of the process and outcome data collection and analysis were significant and related to time pressures, lack of personnel or staff to support this activity, and competing quality improvement initiatives at the institutional home of some genetics centers.