Expression of the familial cardiac valvular dystrophy gene, filamin-A, during heart morphogenesis.

Myxoid degeneration of the cardiac valves is a common feature in a heterogeneous group of disorders that includes Marfan syndrome and isolated valvular diseases. Mitral valve prolapse is the most common outcome of these and remains one of the most common indications for valvular surgery. While the etiology of the disease is unknown, recent genetic studies have demonstrated that an X-linked form of familial cardiac valvular dystrophy can be attributed to mutations in the Filamin-A gene. Since these inheritable mutations are present from conception, we hypothesize that filamin-A mutations present at the time of valve morphogenesis lead to dysfunction that progresses postnatally to clinically relevant disease. Therefore, by carefully evaluating genetic factors (such as filamin-A) that play a substantial role in MVP, we can elucidate relevant developmental pathways that contribute to its pathogenesis. In order to understand how developmental expression of a mutant protein can lead to valve disease, the spatio-temporal distribution of filamin-A during cardiac morphogenesis must first be characterized. Although previously thought of as a ubiquitously expressed gene, we demonstrate that filamin-A is robustly expressed in non-myocyte cells throughout cardiac morphogenesis including epicardial and endocardial cells, and mesenchymal cells derived by EMT from these two epithelia, as well as mesenchyme of neural crest origin. In postnatal hearts, expression of filamin-A is significantly decreased in the atrioventricular and outflow tract valve leaflets and their suspensory apparatus. Characterization of the temporal and spatial expression pattern of filamin-A during cardiac morphogenesis is a crucial first step in our understanding of how mutations in filamin-A result in clinically relevant valve disease.

The neurogenetics of mucolipidosis type IV.

BACKGROUND: Mucolipidosis type IV (MLIV) is an autosomal recessive disease caused by mutations in the MCOLN1 gene that codes for mucolipin, a member of the transient receptor potential (TRP) gene family. OBJECTIVE: To comprehensively characterize the clinical and genetic abnormalities of MLIV. METHODS: Twenty-eight patients with MLIV, aged 2 to 25 years, were studied. Ten returned for follow-up every 1 to 2 years for up to 5 years. Standard clinical, neuroimaging, neurophysiologic, and genetic techniques were used. RESULTS: All patients had varying degrees of corneal clouding, with progressive optic atrophy and retinal dystrophy. Twenty-three patients had severe motor and mental impairment. Motor function deteriorated in three patients and remained stable in the rest. All had a constitutive achlorhydria with elevated plasma gastrin level, and 12 had iron deficiency or anemia. Head MRI showed consistent characteristic findings of a thin corpus callosum and remained unchanged during the follow-up period. Prominent abnormalities of speech, hand usage, and swallowing were also noted. Mutations in the MCOLN1 gene were present in all patients. Correlation of the genotype with the neurologic handicap and corpus callosum dysplasia was found. CONCLUSIONS: MLIV is both a developmental and a degenerative disorder. The presentation as a cerebral palsy-like encephalopathy may delay diagnosis.

C455R notch3 mutation in a Colombian CADASIL kindred with early onset of stroke.

Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is caused by mutations in the notch3 epidermal growth factor-like repeats. A Colombian kindred carries a novel C455R mutation located in the predicted ligand-binding domain. Stroke occurred in the patients at an unusually early age (median age: 31 years) in comparison to the more frequent onset in the fourth decade of life in other CADASIL populations, including a second Colombian kindred with an R1031C mutation.

Genetic association analysis of behavioral inhibition using candidate loci from mouse models.

Genes influence the development of anxiety disorders, but the specific loci involved are not known. Genetic association studies of anxiety disorders are complicated by the complexity of the phenotypes and the difficulty in identifying appropriate candidate loci. We have begun to examine the genetics of behavioral inhibition to the unfamiliar (BI), a heritable temperamental predisposition that is a developmental and familial risk factor for panic and phobic disorders. Specific loci associated with homologous phenotypes in mouse models provide compelling candidate genes for human BI. We conducted family-based association analyses of BI using four genes derived from genetic studies of mouse models with features of behavioral inhibition. The sample included families of 72 children classified as inhibited by structured behavioral assessments. We observed modest evidence of association (P = 0.05) between BI and the glutamic acid decarboxylase gene (65 kDA isoform), which encodes an enzyme involved in GABA synthesis. No significant evidence of association was observed for the genes encoding the adenosine A(1A) receptor, the adenosine A(2A) receptor, or preproenkephalin. This study illustrates the potential utility of using candidate genes derived from mouse models to dissect the genetic basis of BI, a possible intermediate phenotype for panic and phobic disorders.

Prenatal diagnosis of familial dysautonomia by analysis of linked CA-repeat polymorphisms on chromosome 9q31-q33.

Familial Dysautonomia (FD) is an autosomal recessive sensory neuropathy that affects about 1 in 3,700 individuals of Ashkenazi Jewish ancestry. The underlying biochemical and genetic defects are unknown, thereby precluding prenatal diagnosis in at-risk families. Recently, the FD gene (DYS) was mapped with strong linkage disequilibrium to polymorphic markers in the chromosome 9 region q31-q33. In this report, the use of these markers for the prenatal diagnosis of FD by linkage analysis in families with a previously affected child was evaluated. Genomic DNA from appropriate family members was analyzed to construct haplotypes using informative CA repeat polymorphisms closely linked to and flanking the FD locus. The calculation of risk for the prenatal diagnoses was performed by linkage analysis. All seven FD families were informative for the closely linked polymorphic markers and fetal diagnoses were made in eight pregnancies. Six fetal diagnoses were predicted with > 98% accuracy, while two with recombinations were predicted with at least 88% and 92% accuracy. Use of these closely linked markers permitted the reliable prenatal diagnosis of FD in families with a previously affected child.

Molecular characterization of a second melatonin receptor expressed in human retina and brain: the Mel1b melatonin receptor.

A G protein-coupled receptor for the pineal hormone melatonin was recently cloned from mammals and designated the Mel1a melatonin receptor. We now report the cloning of a second G protein-coupled melatonin receptor from humans and designate it the Mel1b melatonin receptor. The Mel1b receptor cDNA encodes a protein of 362 amino acids that is 60% identical at the amino acid level to the human Mel1a receptor. Transient expression of the Mel1b receptor in COS-1 cells results in high-affinity 2-[125I]iodomelatonin binding (Kd = 160 +/- 30 pM). In addition, the rank order of inhibition of specific 2-[125I]iodomelatonin binding by eight ligands is similar to that exhibited by the Mel1a melatonin receptor. Functional studies of NIH 3T3 cells stably expressing the Mel1b melatonin receptor indicate that it is coupled to inhibition of adenylyl cyclase. Comparative reverse transcription PCR shows that the Mel1b melatonin receptor is expressed in retina and, to a lesser extent, brain. PCR analysis of human-rodent somatic cell hybrids maps the Mel1b receptor gene (MTNR1B) to human chromosome 11q21-22. The Mel1b melatonin receptor may mediate the reported actions of melatonin in retina and participate in some of the neurobiological effects of melatonin in mammals.

The gene for achondroplasia maps to the telomeric region of chromosome 4p.

Achondroplasia is the most common type of genetic dwarfism. It is characterized by disproportionate short stature and other skeletal anomalies resulting from a defect in the maturation of the chondrocytes in the growth plate of the cartilage. We have now mapped the achondroplasia gene near the telomere of the short arm of chromosome 4 (4p16.3), by family linkage studies using 14 pedigrees. A positive lod score of z = 3.35 with no recombinants was obtained with an intragenic marker for IDUA. This localization will facilitate the positional cloning of the disease gene.

A gene for Hirschsprung disease (megacolon) in the pericentromeric region of human chromosome 10.

Hirschsprung disease (HSCR) is characterized by a congenital absence of enteric ganglia along a variable length of the intestine. Although long considered to be a multifactorial disease, we have identified linkage in a subset of five HSCR families to the pericentromeric region of chromosome 10, thereby providing monogenic inheritance in some families. A maximum two-point lod score of 3.37 (theta = 0.045) was observed between HSCR and D10S176, under an incompletely penetrant dominant model. Multipoint, affecteds-only and non-parametric analyses supported this finding and localize this gene to a region of approximately 7 centiMorgans, in close proximity to the locus for multiple endocrine neoplasia type 2 (MEN2). The co-occurrence of these two entities in some families might be attributable to shared pathogenetic origins.

Exclusion of familial dysautonomia from more than 60% of the genome.

Familial dysautonomia (FD) is a recessive neurological disorder that affects the development of the sensory and autonomic nervous system. The gene defect appears to be limited to the Ashkenazi Jewish population, where the carrier frequency is 1 in 30. One hundred and ninety-one marker loci representing all autosomes were tested for linkage with the FD genetic defect in 23 families. A combination of pairwise and multipoint analyses excluded the FD gene from at least 60% of the autosomal genome. The program EXCLUDE predicted regions of chromosomes 2, 4, 5q, 9, or 10 as the most promising locations for future analyses.

Linkage analysis of neurofibromatosis type I, using chromosome 17 DNA markers.

The gene for von Recklinghausen neurofibromatosis type 1 (NF1) has recently been mapped to the pericentromeric region of human chromosome 17. To further localize the NF1 gene, linkage analysis using chromosome 17 DNA markers was performed on 11 multigeneration families with 175 individuals, 57 of whom were affected. The markers used were D17Z1 (p17H8), D17S58 (EW301), D17S54 (EW203), D17S57 (EW206), D17S73 (EW207), CRI-L946, HOX-2, and growth hormone. Tight linkage was found between NF1 and D17Z1, D17S58, and D17S57 with a recombination fraction of zero. One recombinant was detected between NF1 and D17S73, showing linkage with a 10% recombination fraction. No linkage was detected between NF1 and CRI-L946 or between HOX-2 and growth hormone. Our data are consistent with the proposed gene order pter D17S58-D17Z1-NF1-D17S57-D17S73 qter.