European Human Genetics Conference 2007 June 16 – 19, 2007 ...

Concurrent Sessions
et Moléculaire, Institut de Neurobiologie Alfred Fessard, Gif sur Yvette, France.
Schwartz-Jampel syndrome (SJS) is a rare autosomal recessive disorder
characterized by permanent and generalized muscle stiffness
(myotonia), and chondrodystrophy. First symptoms appear during
early childhood, and the disease is slowly progressive until adulthood.
SJS is due to hypomorphic mutations in the gene encoding perlecan,
a ubiquitous heparan sulfate proteoglycan secreted within basement
membranes. We have developed a mouse model of SJS by a knock-in
approach, introducing one missense mutation into the perlecan mouse
gene by homologous recombination, to explore the pathophysiological
mechanism of this human disorder.
Homozygous mutant mice were viable with unaffected life span, but
showed a reduced growth and a distinct neuromuscular phenotype
with delayed opening of the eyelids, and flexion of the hind paw when
suspended by the tail. EMG recordings revealed a sustained bursting
activity at rest. Histological analyses of skeletal muscles were suggestive
of denervation-reinnervation events. Major modifications of NMJs
with lack of pretzel-like shape and acetylcholinesterase deficiency
were observed. However, ex-vivo electrophysiological analyses did
not reveal abnormal synaptic transmission. Our results argue for the
accuracy of our mutant mouse line as a model of the disease, demonstrate
that the incomplete perlecan deficiency which characterized
SJS is responsible for major modifications of NMJs, and suggest that
acetylcholinesterase deficiency alone is not responsible for the muscle
hyperexcitability observed in SJS.
C62. Trinucleotide repeat “big jumps” in DM1 transgenic mice:
large CTG expansions, splicing abnormalities and growth
retardation
M. Gomes-Pereira, L. Foiry, A. Nicole, A. Huguet, C. Junien, A. Munnich, G.
Gourdon;
Inserm, U781, Paris, France.
Trinucleotide repeat expansions are the genetic cause of numerous
human diseases, including fragile X mental retardation, Huntington
disease and myotonic dystrophy type 1. Disease severity and age-ofonset
are critically linked to expansion size. Previous mouse models
of repeat instability have not recreated large intergenerational expansions
(“big jumps”), observed when the repeat is transmitted from one
generation to the next, and have never attained the very large tract
lengths possible in humans/patients. We now describe dramatic intergenerational
CTG•CAG repeat expansions of several hundred repeats
in a transgenic mouse model of myotonic dystrophy type 1, resulting
in increasingly severe phenotypic and molecular abnormalities. Homozygous
mice carrying over 700 trinucleotide repeats on both alleles
display severely reduced body size and splicing abnormalities, notably
in the central nervous system. Our findings demonstrate that large
intergenerational trinucleotide repeat expansions can be recreated in
mice, and endorse the use of transgenic mouse models to refine our
understanding of triplet repeat expansion and the resulting pathogenesis.
C63. Recessive severe/lethal osteogenesis imperfecta is caused
by deficiency of proteins comprising the 3-hydroxylation
complex
J. C. Marini 1 , W. Chang 1 , W. A. Cabral 1 , A. M. Barnes 1 , D. R. Eyre 2 , M. Weis 2 ,
R. Morello 3 , B. Lee 3 , S. Leikin 4 , K. Rosenbaum 5 , C. Tifft 5 , D. I. Bulas 5 , C. Kozma
6 , P. Smith 7 , J. J. Mulvihill 8 , U. Sundaram 9 ;
1 BEMB, NICHD/NIH, Bethesda, MD, United States, 2 University of Washington,
Seattle, WA, United States, 3 Baylor College of Medicine, Houston, TX, United
States, 4 SPB, NICHD/NIH, Bethesda, MD, United States, 5 Children’s National
Medical Center, Washington, DC, United States, 6 Georgetown University Medical
Center, Washington, DC, United States, 7 Shriner’s Hospital for Children,
Chicago, IL, United States, 8 University of Oklahoma HSC, Oklahoma City, OK,
United States, 9 VCU/MCV, Richmond, VA, United States.
Osteogenesis imperfecta (OI) is well-known to be caused by dominant
mutations in the genes that code for type I collagen, COL1A1 and
COL1A2. Collagen defects cause about 85% of OI cases. Mutations
that alter the type I collagen primary structure delay helix folding and
allow overmodification of the collagen helix by prolyl 4-hydroxylase,
lysyl hydroxylase and glycosylating enzymes. We have discovered
that essentially all cases of lethal/severe OI without a primary collagen
defect, but with overmodification of the collagen helix, are caused by
null mutations in LEPRE1, encoding prolyl 3-hydroxylase 1 (P3H1), or
CRTAP (cartilage-associated protein), two members of a complex in
the endoplasmic reticulum that 3-hydroxylates only α1(I)Pro986 in type
I collagen. We identified 3 OI probands with null CRTAP mutations and
7 with null LEPRE1 mutations. Five patients with P3H1 defects have a
common LEPRE1 mutant allele, which apparently originated in West
Africa and is also present in African-Americans. All probands have defects
in both alleles and heterozygous carrier parents. Proband mRNA
and protein from the mutant gene is absent or severely reduced.
Mass spectrometry demonstrated absent or residual hydroxylation of
α1(I)Pro986. Interestingly, excess lysyl hydroxylation of proband collagen
helices is comparable to that caused by defects in the primary
structure of the collagen helix, suggesting that helix folding is delayed.
Proband collagen secretion is moderately delayed but total collagen
secretion is increased. These recessive null mutations of CRTAP and
LEPRE1 delineate a novel skeletal paradigm and demonstrate that the
3-hydroxylation complex is crucial for normal bone development.
C64. Left-sided embryonic expression of the BCL-6 corepressor,
BCOR, is required for vertebrate laterality determination
E. N. Hilton 1,2 , F. D. C. Manson 1,3 , J. E. Urquhart 1 , J. J. Johnston 4 , A. M.
Slavotinek 5 , P. Hedera 6 , E. L. Stattin 7 , A. Nordgren 8 , L. G. Biesecker 4 , G. C. M.
Black 2,3 ;
1 Centre for Molecular Medicine, University of Manchester, Manchester, United
Kingdom, 2 Academic Unit of Medical Genetics and Regional Genetic Service,
St Mary’s Hospital, Manchester, United Kingdom, 3 Manchester Royal Eye
Hospital, Central Manchester and Manchester Children’s University Hospitals
NHS Trust, Manchester, United Kingdom, 4 Genetic Disease Research Branch,
National Human Genome Research Institute, National Institutes of Health,
Bethesda, MD, United States, 5 Department of Pediatrics, Division of Genetics,
University of California, San Francisco, CA, United States, 6 Department of
Neurology, Vanderbilt University, Nashville, TN, United States, 7 Department of
Clinical Genetics, Umeå University Hospital, Umeå, Sweden, 8 Department of
Molecular Medicine, Clinical Genetics Unit, Karolinska Institutet, Stockholm,
Sweden.
Oculofaciocardiodental (OFCD) syndrome is an X-linked male lethal
condition encompassing cardiac septal defects, as well as ocular and
dental anomalies. The gene mutated in OFCD syndrome, the BCL-6
corepressor (BCOR), is part of a transcriptional repression complex
whose transcriptional targets remain largely unknown. We reviewed
cases of OFCD syndrome and identified patients exhibiting defective
lateralization including dextrocardia, asplenia and intestinal malrotation,
suggesting that BCOR is required in normal lateral determination
and that the frequent heart problems occurring OFCD syndrome may
be due to defects in this process. To study the function of BCOR we
used morpholino oligonucleotides (MOs) to knockdown expression of
xtBcor in Xenopus tropicalis, thus creating an animal model for OFCD
syndrome. The resulting tadpoles had cardiac and ocular features
characteristic of OFCD syndrome. Reversed cardiac orientation and
disorganized gut patterning was seen when MOs were injected into
the left side of embryos, demonstrating a left-sided requirement for
xtBcor in lateral determination in the frog. Ocular defects displayed no
left-right bias and included anterior and posterior segment disorders
such as microphthalmia and coloboma. Expression of xtPitx2c was
shown to be down regulated when xtBcor was depleted, providing a
mechanism by which xtBcor is required for lateral specification and an
explanation of how BCOR mutation may disrupt cardiac septal development
via the left-right laterality pathway.
C65. USF1 and Dyslipidemias; Insulin dependent expression
of a transcription factor in muscle and fat results in adverse
regulation of target genes
J. Naukkarinen 1 , E. Nilsson 2 , H. A. Koistinen 3 , V. Lyssenko 4 , L. Groop 4 , M. R.
Taskinen 3 , L. Peltonen 1,5 ;
1 National Public Health Institute of Finland and University of Helsinki, Department
of Medical Genetics, Helsinki, Finland, 2 Steno Diabetes center, Gentofte,
Denmark, 3 Department of Medicine, Helsinki University Central Hospital, Helsinki,
Finland, 4 Department of Clinical Sciences, Diabetes and Endocrinology,
Clinical Research Center, Malmo University Hospital, Lund University, Malmo,
Sweden, 5 The Broad Institute, Massachusetts Institute of Technology, Cambridge,
MA, United States.
We recently reported association in Finnish families of allelic variants
of USF1 with FCHL, a common dyslipidemia predisposing to cardiovascular
disease (CVD). This association with dyslipidemia has since
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