Disruption in murine Eml1 perturbs retinal lamination during early development.

During mammalian development, establishing functional neural networks in stratified tissues of the mammalian central nervous system depends upon the proper migration and positioning of neurons, a process known as lamination. In particular, the pseudostratified neuroepithelia of the retina and cerebrocortical ventricular zones provide a platform for progenitor cell proliferation and migration. Lamination defects in these tissues lead to mispositioned neurons, disrupted neuronal connections, and abnormal function. The molecular mechanisms necessary for proper lamination in these tissues are incompletely understood. Here, we identified a nonsense mutation in the Eml1 gene in a novel murine model, tvrm360, displaying subcortical heterotopia, hydrocephalus and disorganization of retinal architecture. In the retina, Eml1 disruption caused abnormal positioning of photoreceptor cell nuclei early in development. Upon maturation, these ectopic photoreceptors possessed cilia and formed synapses but failed to produce robust outer segments, implying a late defect in photoreceptor differentiation secondary to mislocalization. In addition, abnormal positioning of Müller cell bodies and bipolar cells was evident throughout the inner neuroblastic layer. Basal displacement of mitotic nuclei in the retinal neuroepithelium was observed in tvrm360 mice at postnatal day 0. The abnormal positioning of retinal progenitor cells at birth and ectopic presence of photoreceptors and secondary neurons upon maturation suggest that EML1 functions early in eye development and is crucial for proper retinal lamination during cellular proliferation and development.

Alström syndrome is associated with short stature and reduced GH reserve.

INTRODUCTION: Alström syndrome (ALMS) is a rare autosomal recessive monogenic disease included in an emerging class of genetic disorders called 'ciliopathies' and is likely to impact the central nervous system as well as metabolic and endocrine function. Individuals with ALMS present clinical features resembling a growth hormone deficiency (GHD) condition, but thus far no study has specifically investigated this aspect in a large population. MATERIAL AND METHODS: Twenty-three patients with ALMS (age, 1-52 years; 11 males, 12 females) were evaluated for anthropometric parameters (growth charts and standard deviation score (SDS) of height, weight, BMI), GH secretion by growth hormone-releasing hormone + arginine test (GHRH-arg), bone age, and hypothalamic-pituitary magnetic resonance imaging (MRI). A group of 17 healthy subjects served as controls in the GH secretion study. Longitudinal retrospective and prospective data were utilized. RESULTS: The length-for-age measurements from birth to 36 months showed normal growth with most values falling within -0·67 SDS to +1·28 SDS. A progressive decrease in stature-for-age was observed after 10 years of age, with a low final height in almost all ALMS subjects (>16-20 years; mean SDS, -2·22 ± 1·16). The subset of 12 patients with ALMS tested for GHRH-arg showed a significantly shorter stature than age-matched controls (154·7 ± 10·6 cm vs 162·9 ± 4·8 cm, P = 0·009) and a mild increase in BMI (Kg/m(2) ) (27·8 ± 4·8 vs 24·1 ± 2·5, P = 0·007). Peak GH after GHRH-arg was significantly lower in patients with ALMS in comparison with controls (11·9 ± 6·9 µg/l vs 86·1 ± 33·2 µg/l, P < 0·0001). Severe GHD was evident biochemically in 50% of patients with ALMS. The 10 adult ALMS patients with GHD showed a reduced height in comparison with those without GHD (149·7 ± 6·2 cm vs 161·9 ± 9·2 cm, P = 0·04). MRIs of the diencephalic and pituitary regions were normal in 11 of 12 patients. Bone age was advanced in 43% of cases. CONCLUSIONS: Our study shows that 50% of nonobese ALMS patients have an inadequate GH reserve to GHRH-arg and may be functionally GH deficient. The short stature reported in ALMS may be at least partially influenced by impairment of GH secretion.

Molecular analysis and long-term clinical evaluation of three siblings with Alström syndrome.

Alström syndrome is a rare, autosomal recessive disorder characterized by a wide spectrum of clinical features including early-onset retinal degeneration leading to blindness, sensorineural hearing loss, short stature, obesity, type 2 diabetes, hyperlipidemia and dilated cardiomyopathy. Renal, hepatic and pulmonary dysfunction may occur in the later phases of the disease. The three affected sisters, from a consanguineous Turkish family, with the characteristic features of Alström syndrome, were clinically diagnosed in 1987 and followed for 20 years. DNA sequence analysis of ALMS1, the causative gene in Alström syndrome, identified a novel homozygous disease-causing mutation, c.8164C>T, resulting in a premature termination codon in exon 10 in each of the three affected sisters. Furthermore, we describe the longitudinal disease progression in this family and report new clinical findings likely associated with Alström syndrome, such as pes planus and hyperthyroidism.

Alms1-disrupted mice recapitulate human Alström syndrome.

Mutations in the human ALMS1 gene cause Alström syndrome (AS), a progressive disease characterized by neurosensory deficits and by metabolic defects including childhood obesity, hyperinsulinemia and Type 2 diabetes. Other features that are more variable in expressivity include dilated cardiomyopathy, hypertriglyceridemia, hypercholesterolemia, scoliosis, developmental delay and pulmonary and urological dysfunctions. ALMS1 encodes a ubiquitously expressed protein of unknown function. To obtain an animal model in which the etiology of the observed pathologies could be further studied, we generated a mouse model using an Alms1 gene-trapped ES cell line. Alms1-/- mice develop features similar to patients with AS, including obesity, hypogonadism, hyperinsulinemia, retinal dysfunction and late-onset hearing loss. Insulin resistance and increased body weight are apparent between 8 and 12 weeks of age, with hyperglycemia manifesting at approximately 16 weeks of age. In addition, Alms1-/- mice have normal hearing until 8 months of age, after which they display abnormal auditory brainstem responses. Diminished cone ERG b-wave response is observed early, followed by the degeneration of photoreceptor cells. Electron microscopy revealed accumulation of intracellular vesicles in the inner segments of photoreceptors, whereas immunohistochemical analysis showed mislocalization of rhodopsin to the outer nuclear layer. These findings suggest that ALMS1 has a role in intracellular trafficking.

Characterization of the murine Lbx2 promoter, identification of the human homologue, and evaluation as a candidate for Alström syndrome.

The murine Lbx2 gene is a member of the ladybird family of homeobox genes, which is expressed in the developing urogenital system, eye, and brain. Using transgenic mice, we demonstrate that 9 kb of the 5' flanking region of mouse Lbx2 is able to direct expression of a reporter gene in a tissue-specific manner recapitulating the endogenous expression pattern. This regulatory region provides a novel reagent allowing for transgenic expression in the developing urogenital ridge. In addition, we describe the identification of the human homologue, LBX2. Comparison of the human LBX2 and mouse Lbx2 sequences upstream of the coding regions reveals sequence conservation suggesting conserved regulatory regions. Both the human LBX2 and the mouse Lbx2 genes have similar genomic structures and are composed of two exons separated by an intron. We mapped the mouse Lbx2 gene to 35 cM on chromosome 6 and the human LBX2 gene to a homologous region of chromosome 2p13. This is a candidate region for several inherited disorders, including Alström syndrome, a disorder that includes ocular, urogenital, and renal abnormalities. Given the expression pattern of Lbx2, the chromosomal location in humans, and the potential function of mammalian ladybird genes, we have begun to analyze patients with ocular disorders and those with Alström syndrome for mutations in LBX2. Although polymorphisms were identified, our results indicate that mutations in the coding region of LBX2 do not account for Alström syndrome in the six kindreds analyzed.

Alström syndrome: further evidence for linkage to human chromosome 2p13.

Alström syndrome is a rare autosomal recessive disorder characterized by retinal degeneration, sensorineural hearing loss, early-onset obesity, and non-insulin-dependent diabetes mellitus. The gene for Alström syndrome (ALMS1) has been previously localized to human chromosome 2p13 by homozygosity mapping in two distinct isolated populations - French Acadian and North African. Pair-wise analyses resulted in maximum lod (logarithm of the odds ratio) scores of 3.84 and 2.9, respectively. To confirm these findings, a large linkage study was performed in twelve additional families segregating for Alström syndrome. A maximum two-point lod score of 7.13 (theta = 0.00) for marker D2S2110 and a maximum cumulative multipoint lod score of 9.16 for marker D2S2110 were observed, further supporting linkage to chromosome 2p13. No evidence of genetic heterogeneity was observed in these families. Meiotic recombination events have localized the critical region containing ALMS1 to a 6.1-cM interval flanked by markers D2S327 and D2S286. A fine resolution radiation hybrid map of 31 genes and markers has been constructed.

Susceptibility to testicular germ-cell tumours in a 129.MOLF-Chr 19 chromosome substitution strain.

The identification of genes that control susceptibility to testicular germ-cell tumours (TGCTs), the most common cancer affecting young men, has been difficult. In laboratory mice, TGCTs arise from primordial germ cells in only the 129 inbred strains, and susceptibility is under multigenic control. The spontaneously arising mutation Ter (ref. 5) on mouse chromosome 18 (Refs 6,7) increases TGCT frequency on a 129/Sv background. We originally used Ter in genetic crosses to identify loci that control tumorigenesis. A genome scan of tumour-bearing progeny from backcrosses between the 129/Sv-Ter/+ and MOLF/Ei strains provided modest evidence that MOLF-derived alleles on chromosome 19 enhance development of bilateral TGCTs (ref. 9). To obtain independent evidence for linkage to the MOLF chromosome, we made an autosomal chromosome substitution strain (CSS; or 'consomic strain') in which chromosome 19 of 129/Sv+/+ was replaced by its MOLF-derived homologue. The unusually high frequency of TGCTs in this CSS (even in the absence of the Ter mutation) provides evidence confirming the genome survey results, identifies linkage for a naturally occurring strain variant allele that confers susceptibility to TGCTs and illustrates the power of CSSs in complex trait analysis.

Quantitative trait loci analysis for the differences in susceptibility to atherosclerosis and diabetes between inbred mouse strains C57BL/6J and C57BLKS/J.

Mice from the inbred strain C57BLKS/J (BKS) exhibit increased susceptibility to both diabetes and atherosclerosis compared to C57BL/6J (B6) mice. To determine whether the differences in diabetes and atherosclerosis are related, we carried out a cross between B6-db/db and BKS. We selected 99 female F2-db/db progeny, tested the progeny for plasma lipids, plasma glucose, and fatty-streak lesions, and used quantitative trait loci (QTL) analysis to identify the chromosomal regions associated with these phenotypes. No major QTL were found for total cholesterol, VLDL-cholesterol, or triglycerides. Two suggestive QTL were found for HDL-cholesterol (LOD scores of 2. 7 and 2.8), and two suggestive loci were found for plasma glucose (LOD scores of 2.3 and 2.0). Lesion size was not correlated with plasma lipid levels or glucose. Lesion size was determined by a locus at D12Mit49 with a LOD score of 2.5 and a significant likelihood ratio statistic. The gene for apolipoprotein apoB lies within the region, but apoB levels were similar in strains B6 and BKS. The QTL on Chr 12 was confirmed by constructing a congenic strain with BKS alleles in the QTL region on a B6 genetic background. We conclude that susceptibilities to diabetes and atherosclerosis are not conferred by the same genes in these strains and that a major gene on Chr 12, which we name Ath6, determines the difference in atherosclerosis susceptibility.

Human DCTN1: genomic structure and evaluation as a candidate for Alström syndrome.

The human dynactin 1 gene (DCTN1) is positioned on chromosome 2p13, the candidate region for various diseases including Alström syndrome, limb-girdle muscle dystrophy, and Miyoshi myopathy. Here, we report the exon-intron structure of DCTN1 along with characterization of the 5' upstream sequence and alternative splice variants previously identified by Tokito et al. (1996), Mol. Biol. Cell 7: 1167-1180). Knowledge of the genomic structure of DCTN1allowed us to design intronic primers necessary for analyzing mutations in families segregating for diseases linked to this gene. These primers were tested on a French Acadian kindred segregating for Alström syndrome. No mutations were observed within the coding region of DCTN1 in this family. However, the intronic primers should allow for the rapid amplification of the coding region for mutational analysis of additional Alström families and other diseases tightly linked to the DCTN1locus on chromosome 2p13.

Testicular teratocarcinogenesis in mice--a review.

Spontaneous testicular germ cell tumours in humans and mice are remarkable for their diverse composition. These tumours are usually composed of an extraordinary variety of cell and tissue types including muscle, skin, bone, cartilage, and neuroepithelia. Their diverse composition reflects their origin from totipotent primordial germ cells at about Day 12 of fetal development. Although much is known about the development of these tumours, remarkably little is known about the genetics of the mammalian primordial germ cell lineage or about the genes that control susceptibility to spontaneous testicular germ cell tumours in humans or mice. Conventional genetic analysis of susceptible 129/Sv mice is difficult because of the large number of susceptibility genes and their low penetrance. We are taking advantage of the Ter mutation to simplify the genetic analysis. Various evidence suggests that Ter is neither necessary nor sufficient for tumourigenesis. Instead, Ter acts as a modifier, dramatically increasing tumour incidence from approximately 1% in +/+ males, to approximately 17% in Ter/+ males and approximately 94% in Ter/Ter males. Segregation analysis suggests that Ter increases tumour incidence by requiring some, but perhaps not all, of the 129/Sv-derived susceptibility genes. With standard crosses that segregate for the Ter mutation, identification not only of Ter but also of these 129/Sv-derived susceptibility genes should be possible. In this paper, we review the genetics and development of germ cell tumours in 129/Sv mice, summarize the status of Ter mapping, and provide evidence that different genetic pathways lead to unilateral and bilateral tumours.

Homozygosity mapping at Alström syndrome to chromosome 2p.

Alström syndrome is a rare autosomal recessive disorder characterized by pigmentary retinal degeneration, sensorineural hearing loss, childhood obesity, non-insulin-dependent diabetes mellitus, hyperlipidemia and chronic nephropathy. Features occasionally observed include acanthosis nigricans, hypogonadism, hypothyroidism, alopecia, short stature and cardiomyopathy. We report here the results of a linkage study in a large French Acadian kindred, as a first step in identifying the molecular basis of Alström syndrome. Evidence of a founder effect made if feasible to use a homozygosity mapping strategy to identify the chromosomal location of the Alström gene. In a genome-wide screen, haplotype sharing for a region on chromosome 2 was observed in all affected individuals. Two point linkage analysis resulted in a maximum lod score of 3.84 (theta = 0.00) for marker D2S292. By testing additional markers, the disease gene was localized to a 14.9 cM region on chromosome 2p.

Physical and genetic mapping of novel microsatellite polymorphisms on human chromosome 19.

We describe here the identification of 11 novel microsatellite polymorphisms on human chromosome 19. These dinucleotide repeat polymorphisms were detected in chromosome 19-specific cosmids that were physically mapped by fluorescence in situ hybridization. For each repeat, flanking oligonucleotide primers were synthesized and the polymerase chain reaction assay was performed on a panel of 100 unrelated individuals to determine the heterozygosity and allele frequencies. To characterize these markers further, genetic and radiation hybrid maps were constructed. These microsatellite polymorphisms will be valuable in further linkage analysis of inherited diseases on chromosome 19p.