Catecholamines in patients with 22q11.2 deletion syndrome and the low-activity COMT polymorphism.

OBJECTIVE: To investigate catecholamine phenotypes and the effects of a tyrosine hydroxylase inhibitor in individuals with the 22q11.2 deletion syndrome and low-activity catechol-O-methyltransferase (COMT). BACKGROUND: Many persons with the 22q11.2 deletion syndrome suffer severe disability from a characteristic ultrarapid-cycling bipolar disorder and associated "affective storms." One etiologic hypothesis for this condition is that deletion of the COMT gene from one chromosome 22 results in increased catecholamine neurotransmission, particularly if the undeleted chromosome 22 encodes a variant of COMT with low activity. METHODS: In a preliminary study, plasma, urine, and CSF catecholamines and catecholamine metabolites were measured in four teenage patients with a neuropsychiatric condition associated with 22q11.2 deletion and the low-activity COMT polymorphism on the nondeleted chromosome. In these four patients, and an additional institutionalized adult with the condition, an uncontrolled, open-label trial of metyrosine was administered in an attempt to lower catecholamine production and to alleviate symptoms. RESULTS: Mild elevations of baseline CSF homovanillic acid (HVA) were found in three of four patients and a moderate reduction in CSF HVA after metyrosine treatment in the patient with the highest pretreatment concentration. The course of the five patients during the clinical trial is described. CONCLUSIONS: In patients with the 22q11.2 deletion syndrome and low-activity COMT, controlled studies of pharmacologic agents that decrease catecholamine production, block presynaptic catecholamine storage, or enhance S-adenosylmethionine, the cosubstrate of COMT, are warranted.

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.

Expansile bone lesions in a three-generation family.

We report on a three-generation family with "expansile" bone lesions of the distal radius and ulna, cortical thickening of the proximal long bones, and pathologic fractures. The differential diagnosis of expansile bone lesions includes isolated bone cysts and tumors, such as enchondromas and fibrous dysplasia; familial expansile osteolysis; and the genochondromatoses. Our patients have findings most similar to the genochondromatoses; however, the distribution of the lesions and the accompanying manifestations may be evidence for a unique genetic condition in this family.

Structure and chromosomal localization of the beta2 subunit of the human brain sodium channel.

The beta2 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 beta2 subunit. The mature human beta2 protein has 89% amino acid sequence identity to rat beta2 and has four conserved consensus sites for N-linked glycosylation. The extracellular 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 beta2 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 beta2 to cell adhesion molecules, including myelin protein p0, and its chromosomal location at 11q23 suggest a potential role in these demyelinating diseases.

Human huntingtin derived from YAC transgenes compensates for loss of murine huntingtin by rescue of the embryonic lethal phenotype.

Huntington disease (HD) is caused by expansion of a CAG trinucleotide repeat in exon 1 of a novel gene. The HD protein (huntingtin) plays a critical role in early embryonic development since homozygous targeted disruption of the murine HD gene results in embryonic lethality by day 7.5. To rescue this phenotype by transgene based huntingtin expression it is therefore essential to express the protein early enough in development in the appropriate cells. Since YAC based transgenes are known to be regulated in an appropriate temporal and tissue-specific manner, we sought to rescue the embryonic lethality by breeding YAC transgenic mice expressing human huntingtin with mice heterozygous for the targeted disruption. We generated viable offspring homozygous for the disrupted murine HD gene but expressing human huntingtin derived from the YAC. This result clearly shows that YAC transgene based expression of huntingtin occurs prior to 7.5 days gestation. Additionally, we show that human huntingtin expression in YAC transgenic mice follows an identical tissue distribution and subcellular localisation pattern as that of the murine endogenous protein and that expression levels of 2-3 times endogenous can be achieved. This shows that human huntingtin under the influence of its native promoter, despite differences to the murine protein, is functional in a murine background and can compensate for loss of the murine protein. These results show that YAC transgenic approaches are a particularly promising route to producing an animal model for disorders associated with CAG expansion.

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.

cDNA cloning and chromosome mapping of the human Fe65 gene: interaction of the conserved cytoplasmic domains of the human beta-amyloid precursor protein and its homologues with the mouse Fe65 protein.

Using the yeast two hybrid system, a mouse embryo cDNA library was screened for proteins that interact with the C-terminus of the human beta-amyloid precursor protein (beta PP). A fusion protein was identified that interacts specifically with the cytoplasmic domain of beta PP and does not interact with the beta-amyloid region. The protein encoded by this partial mouse cDNA is identical to the C-terminus of the rat Fe65 protein. This mouse protein also interacts with the homologous C-terminal domains of the mouse amyloid precursor-like proteins, APLP1 and APLP2. These conserved cytoplasmic regions contain a common amino acid motif, Asn-Pro-Thr-Tyr, which has previously been shown to influence both the secretion and internalization of beta PP. Fe65 has been implicated in regulatory and cell signaling mechanisms because it contains two different motifs involved in protein binding, a WW domain (a variant of Src homology 3 domains) and a phosphotyrosine interaction domain (PID). Interestingly, the PID domain binds to the same motif present in the conserved cytoplasmic domains of the beta PP and beta PP-like proteins. RNA analyses reveal that Fe65 is predominantly expressed in brain and in the regions most affected by Alzheimer's disease (AD)-associated neuropathology. The human Fe65 mRNA was cloned from a fetal brain cDNA library. The message encodes a protein of 735 amino acids that is 95% identical to the rat Fe65 protein. The human Fe65 gene was mapped on human metaphase chromosomes to band 11p15 using fluorescence in situ hybridization.

Isolation, mapping, and functional expression of the mouse X chromosome glycerol kinase gene.

Glycerol kinase (Gyk) participates in the metabolism of endogenously derived and dietary glycerol. Deficiency of the human enzyme activity is an X-linked recessive disorder with a clinical picture varying from childhood metabolic crisis to asymptomatic adults incidentally identified by hyperlipidemia screening (pseudohypertriglyceridemia). Gyk is a member of a small group of kinases termed ambiquitous enzymes that are found in the cytosol or as membrane-bound enzymes associated with the voltage-dependent anion channel of the mitochondrial outer membrane. It was recently reported that in humans there are X-linked and autosomal copies of Gyk sequences, both apparently functional genes and processed pseudogenes. To understand the role of Gyk in normal metabolism and the variable clinical features seen with Gyk deficiency, we have characterized the mouse Gyk gene. We present the sequence of a full-length mouse Gyk cDNA that is alternatively spliced in brain. The Gyk gene was mapped to the mouse X chromosome by both fluorescence in situ hybridization and an interspecies backcross panel, demonstrating conservation of synteny with dmd. To confirm the functional identity of the cDNA, transient transfection of the cDNA into COS7 cells was shown to cause a marked elevation in glycerol kinase activity.

A candidate gene for the amnionless gastrulation stage mouse mutation encodes a TRAF-related protein.

We report the identification of a new recessive prenatal lethal insertional mutation, amnionless (amn). amn mutant embryos first appear abnormal during the Early Streak stage, between E6.5 and E7.0, when they initiate mesoderm production. Subsequently, the amn mutants become developmentally arrested between the Mid and Late Streak stages of gastrulation and they die and are resorbed between E9.5 and E10.5. While extraembryonic structures, including the chorion, yolk sac blood islands, and allantois appear to develop normally, the small embryonic ectoderm remains undifferentiated and generates no amnion. In addition, the embryonic mesoderm that is produced does not become organized into node, notochord, and somites and there is no morphological evidence of neural induction. Interspecific backcross and fluorescence in situ hybridization analyses map the transgene insertion, and thus the amn mutation, to the distal region of mouse chromosome 12, which has synteny with human chromosome 14q32. A gene encoding a 7.5-kb transcript has been identified at a junction between the integrated transgene and host chromosome 12 sequences that meets three criteria expected of a candidate amn gene. This gene maps to the site of transgene insertion; it is transcribed during gastrulation, and its expression is disrupted in amn mutant embryos. Nucleotide sequencing studies show that the 567 amino acid protein encoded by the 7.5-kb transcript is a member of the newly defined family of putative signal transducing proteins, TRAFs, that associate with the cytoplasmic domains of members of the tumor necrosis factor (TNF) receptor superfamily. Thus, we have named the gene encoding the 7. 5-kb transcript TRAFamn. TRAFamn is identical to a recently reported protein (CD40bp, CAP-1, CRAF1, LAP1) that can bind the cytoplasmic domains of CD40 and the lymphotoxin beta receptor (LTbetaR), both of which are known members of the TNF receptor superfamily. The implications of these findings regarding a possible role for the TNF receptor superfamily during gastrulation are discussed.

A new region of conservation is defined between human and mouse X chromosomes.

Comparative mapping of the X chromosome in eutherian mammals has revealed distinct regions of conservation as well as evolutionary rearrangements between human and mouse. Recently, we and others mapped the murine homologue of CLCN4 (Chloride channel 4) to band F4 of the X chromosome in Mus spretus but to chromosome 7 in laboratory strains. We now report the mapping of the murine homologues of APXL (Apical protein Xenopus laevis-like) and OA1 (Ocular albinism type I), two genes that are located on the human X chromosome at band p22. 3 and in close proximity to CLCN4. Interestingly, Oa1 and Apxl map to bands F2-F3 in both M. spretus and the laboratory strain C57BL/6J, defining a new rearrangement between human and mouse X chromosomes.

Mouse autosomal homolog of DAZ, a candidate male sterility gene in humans, is expressed in male germ cells before and after puberty.

Deletion of the Azoospermia Factor (AZF) region of the human Y chromosome results in spermatogenic failure. While the identity of the critical missing gene has yet to be established, a strong candidate is the putative RNA-binding protein DAZ (Deleted in Azoospermia). Here we describe the mouse homolog of DAZ. Unlike human DAZ, which is Y-linked, in mouse the Dazh (DAZ homolog) gene maps to chromosome 17. Nonetheless, the predicted amino acid sequences of the gene products are quite similar, especially in their RNP/RRM (putative RNA-binding) domains, and both genes are transcribed predominantly in testes; the mouse gene is transcribed at a lower level in ovaries. Dazh transcripts were not detected in testes of mice that lack germ cells. In testes of wildtype mice, Dazh transcription is detectable 1 day after birth (when the only germ cells are prospermatogonia), increases steadily as spermatogonial stem cells appear, plateaus as the first wave of spermatogenic cells enters meiosis (10 days after birth), and is sustained at this level thereafter. This unique pattern of expression suggests that Dazh participates in differentiation, proliferation, or maintenance of germ cell founder populations before, during, and after the pubertal onset of spermatogenesis. Such functions could readily account for the diverse spermatogenic defects observed in human males with AZF deletions.

Partial characterization of the genome of nine animal caliciviruses.

Caliciviruses (CVs) include at least 42 distinct serotypes. Seventeen CV serotypes have been isolated from marine sources and are called San Miguel sea lion caliciviruses (SMSVs). CVs also have been isolated from reptiles, primates, and other terrestrial animals. Nucleotide sequences from portions of genome of prototype strains for six SMSV serotypes, the reptile CV, Cro-1, the cetacean CV, Tur-1, and the primate CV, Pan-1, are presented. cDNA products of the polymerase (all strains characterized) and capsid (SMSV-17) regions were produced by reverse transcription-polymerase chain reaction using Pan-1 primers. Comparisons of nucleotide and amino acid identity among these and published CV sequences indicated that the nine characterized CVs fall into a phylogenetic group that includes SMSV-1 and SMSV-4 and that is more closely related to other characterized animal CVs than to most human CVs. The phylogenetic analysis also indicated that distinct genera exist among the Caliciviridae. SMSV-17 and SMSV-4 are predicted to be closer to each other than other caliciviruses of known serotype; 574 (82%) of the 704 amino acids in the SMSV-17 and SMSV-4 capsid genes were identical.

Recent developments with human caliciviruses.

Caliciviruses (CVs) are human and animal pathogens. The best known human CVs are Norwalk virus (NV) and Snow Mountain agent. Recent molecular studies have confirmed that CVs are a unique taxonomic family. These molecular studies also have clarified relationships among previously poorly characterized human enteric viruses, led to new diagnostic tests and identified potential relationships between human and animal CVs. The purpose of this review was to describe these recent developments.