Mitochondrial DNA mutation associated with Leber's hereditary optic neuropathy.

Leber's hereditary optic neuropathy is a maternally inherited disease resulting in optic nerve degeneration and cardiac dysrhythmia. A mitochondrial DNA replacement mutation was identified that correlated with this disease in multiple families. This mutation converted a highly conserved arginine to a histidine at codon 340 in the NADH dehydrogenase subunit 4 gene and eliminated an Sfa NI site, thus providing a simple diagnostic test. This finding demonstrated that a nucleotide change in a mitochondrial DNA energy production gene can result in a neurological disease.

Familial renal glycosuria: a genetic reappraisal of hexose transport by kidney and intestine.

Renal glucose titration studies were carried out in 10 members of two pedigrees with familial renal glycosuria to test the accepted hypothesis of autosomal dominant inheritance and to investigate the genetic significance of "type A" and "type B" renal glycosuria. In one family, a brother and sister each had a moderately reduced threshold and tubular maximum for glucose (type A), but both of their parents reabsorbed glucose normally. In the second family, two brothers had severe type A renal glycosuria, their mother and one brother had a mild type A defect, and another brother demonstrated a reduced threshold, an exaggerated splay, and a normal tubular maximum, indicative of type B glycosuria.Hexose transport by intestinal mucosa was also investigated in controls and in the three brothers with the most severe renal glycosuria. D-glucose-(14)C and 3-O-methylglucose-(14)C were accumulated by jejunal mucosa from controls by processes which were saturable and concentrative. No differences in hexose transport were observed in the patients with renal glycosuria. We conclude that familial renal glycosuria can be inherited as an autosomal recessive trait; that mild and severe type A renal glycosuria and type B renal glycosuria can occur in the same pedigree; and that defective reabsorption of glucose by the kidney need not be accompanied by abnormalities in intestinal glucose transport. These findings indicate that glucose transport in the gut and kidney are not mediated by identical mechanisms, and that several different mutations are responsible for the phenotypic variability in familial renal glycosuria.

Renal and intestinal hexose transport in familial glucose-galactose malabsorption.

Glucose transport by jejunal mucosa in vitro and kidney in vivo was investigated in a 3 yr old patient with congenital glucose-galactose malabsorption, her family, and 16 normal volunteers. Glucose transport by normal human jejunal mucosa was concentrative, saturable, sodium and energy dependent, and exhibited competitive inhibition. Biopsy specimens from six normal controls and an asymptomatic 5 yr old brother of the proband accumulated glucose to concentrations 16 times that in the incubation medium. The proband's mucosa was unable to concentrate glucose throughout a 60 min incubation period. Both of her parents and a half sister demonstrated impaired glucose transport. Their values fell between normal and those of the proband. Influx of glucose was impaired but efflux of glucose from the mucosa of these three heterozygotes was identical with that in three normal controls. A kinetic analysis indicated a reduced capacity (V(max)), but a normal affinity (K(m)) for glucose transport by their intestinal mucosa. All subjects accumulated fructose similarly.Renal glucose transport was investigated using renal glucose titration techniques. A partial defect in renal glucose reabsorption was found in the proband. Her brother's titration curve was similar to that of seven normal volunteers. We conclude that familial glucose-galactose malabsorption is inherited as an autosomal recessive trait, that heterozygotes for this disorder are detectable and demonstrate a reduced capacity for glucose transport, and that absent intestinal glucose transport is accompanied by partial impairment of renal glucose transport.

A patient with Ehlers-Danlos syndrome type VI is a compound heterozygote for mutations in the lysyl hydroxylase gene.

In the present study, we have isolated and sequenced the complementary DNAs of two mutant alleles for lysyl hydroxylase (LH) in fibroblasts from one patient (AT750) with Ehlers-Danlos syndrome type VI (EDS VI). We have identified a putative mutation in each allele which may be responsible for the patient's decreased LH (normalized to prolyl hydroxylase) activity (24% of normal). Intermediate levels of LH activity were measured in the patient's parents, who are clinically normal (father 52%; mother 86%). After the cloning of cDNAs and amplification by PCR, sequence analysis revealed two equally distributed populations of cDNAs for LH in the AT750 cell line. Each allele revealed different but significant changes from the normal sequence. In one allele (allele 1), the most striking change was a triple base deletion that would result in the loss of residue Glu532. The most significant difference in the other allele (allele 2) was a G-->A change which would produce a Gly678-->Arg codon change in a highly conserved region of the enzyme. Restriction analysis identified that allele 1 was inherited from the proband's mother and allele 2 from the father. This study represents the first example of compound heterozygosity for the LH gene in an EDS VI patient, and it appears that there is an additive effect of each mutant allele on clinical expression in this patient.

Absence of branched chain acyl-transferase as a cause of maple syrup urine disease.

Decreased function of human mitochondrial branched chain alpha-ketoacid dehydrogenase complex results in branched chain ketoacidemia or maple syrup urine disease. Activity of this multienzyme complex varies from 0 to approximately 15% of wild type branched chain alpha-ketoacid dehydrogenase complex activity within the population of homozygous affected individuals. We used the technique of Western Blotting with antibodies against purified bovine liver branched chain alpha-ketoacid dehydrogenase complex to screen mitochondrial proteins from cultured human fibroblasts for immunocrossreactive proteins. This method probes the physical structure of the proteins forming this multienzyme complex. One patient with branched chain ketoacidemia lacked an immunoreactive transacylase protein. This protein catalyzes the transfer of the branched chain acyl group from the decarboxylase to reduced coenzyme A. Kinetic analysis of the enzyme activity in cell lysates from this patient confirmed that the complex would not utilize coenzyme A. Thus, we have defined a structural basis for an impaired multienzyme complex of mitochondria in man.

RAI1 variations in Smith-Magenis syndrome patients without 17p11.2 deletions.

BACKGROUND: Smith-Magenis syndrome (SMS) (OMIM No 182290) is a mental retardation syndrome characterised by behavioural abnormalities, including self injurious behaviours, sleep disturbance, and distinct craniofacial and skeletal anomalies. It is usually associated with deletion involving 17p11.2 and is estimated to occur in 1/25,000 births. Heterozygous frameshift mutations leading to protein truncation in retinoic acid induced 1 gene (RAI1) have been identified in individuals with phenotypic features consistent with SMS. RAI1 lies within the 17p11.2 locus, but these patients did not have 17p11.2 deletions. OBJECTIVE: Analysis of four individuals with features consistent with SMS for variations in RAI1, using a polymerase chain reaction and sequencing strategy. None of these patients carry 17p11.2 deletions. RESULTS: Two patients had small deletions in RAI1 resulting in frameshift and premature truncation of the protein. Missense mutations were identified in the other two. Orthologs across other genomes showed that these missense mutations occurred in identically conserved regions of the gene. The mutations were de novo, as all parental samples were normal. Several polymorphisms were also observed, including new and reported SNPs. The patients' clinical features differed from those found in 17p11.2 deletion by general absence of short stature and lack of visceral anomalies. All four patients had developmental delay, reduced motor and cognitive skills, craniofacial and behavioural anomalies, and sleep disturbance. Seizures, not previously thought to be associated with RAI1 mutations, were observed in one patient of the cohort. CONCLUSIONS: Haploinsufficiency of the RAI1 gene is associated with most features of SMS, including craniofacial, behavioural, and neurological signs and symptoms.

Glucose transport by cultured human fibroblasts: regulation by phorbol esters and insulin.

The regulation of 3-O-methyl-D-glucose (OMG) uptake by insulin and phorbol esters was studied in cultured human skin fibroblasts. Insulin rapidly stimulated OMG uptake through a mechanism independent of new protein synthesis. Maximal insulin effect was reached in 30 min and remained constant up to 12 h. The protein kinase C activators 12-O-tetradecanoyl phorbol 13-acetate (TPA) and phorbol 12,13-dibutyrate (PdBU) promoted an initial rapid stimulation followed by a secondary long-term rise of OMG influx. This latter effect of phorbol esters on OMG influx began after 1 h, reached a maximum in 12-15 h, and was prevented by the simultaneous addition of protein synthesis inhibitors, suggesting that phorbol esters increased the synthesis of new glucose transporters. In accord with this interpretation, phorbol esters, but not insulin, increased mRNA levels for two distinct glucose transporters (GLUT1 and GLUT3) in human fibroblasts. Both the rapid and the long-term effects of phorbol esters on OMG influx were dose-dependent and half-maximal stimulations occurred at 15 nM for both PdBU and TPA. Kinetic analysis of OMG uptake indicated that both effects of phorbol esters were associated with an increase in the Vmax of the transport process, with no significant changes of the Km (4-6 mM). These results suggest that, in human fibroblasts, phorbol esters, unlike insulin, produce a long-term stimulation of OMG uptake, which is dependent upon protein synthesis and is associated with increased levels of GLUT1 and GLUT3 mRNA.

A [3H]lysine-containing synthetic peptide substrate for human protocollagen lysyl hydroxylase.

A tridecapeptide containing tritium-labelled lysine and corresponding closely to residues 98 to 110 of the alpha chain of type I collagen was synthesized by the solid-phase method. Gly-Leu-Hyp-Gly-Nle-[4,5-3H]Lys-Gly-His-Arg-Gly-Phe-Ser-Gly was used as a substrate of human protocollagen lysyl hydroxylase (peptidyllysine, 2-oxoglutarate: oxygen 5-oxidoreductase, EC 1.14.11.4) obtained from dermal fibroblasts. L-[4,5-3H]Lysine was converted to N alpha-t-butyloxycarbonyl-N epsilon-o-chlorobenzyloxycarbonyl [3H]lysine which was incorporated during stepwise synthesis of the peptide. The chemical and radiochemical purities and specific activity of the completed peptide were characterized. A non-radiolabelled analogue of the peptide inhibited the hydroxylation of [3H]lysine-containing protocollagen by human lysyl hydroxylase, indicating that the synthetic peptide interacted with the enzyme. The peptide containing [3H]lysine was a substrate for lysyl hydroxylase and permitted direct measurement of enzyme activity in relatively crude cell extracts by a tritium-release assay. Extracts of cultured fibroblasts from a patient with an autosomal recessive pattern of inheritance for Ehlers-Danlos syndrome type VI had activities for tritium release from either the radiolabelled synthetic peptide or from [3H]lysine-containing protocollagen that were only 30% of those from control cells. These data indicate that a stable, well-defined synthetic peptide containing [3H]lysine is a useful substrate for studies of genetically variant lysyl hydroxylase from cultured human cells.

Cystathionine beta-synthase deficiency in Georgia (USA): correlation of clinical and biochemical phenotype with genotype.

Cystathionine beta-synthase (CBS) deficiency is a rare autosomal recessive disorder that is the most frequent cause of clinical homocystinuria. Patients not treated in infancy have multi-systems disorders including dislocated lenses, mental deficiency, osteoporosis, premature arteriosclerosis, and thrombosis. In this paper, we examine the relationship of the clinical and biochemical phenotypes with the genotypes of 12 CBS deficient patients from 11 families from the state of Georgia, USA. By DNA sequencing of all of the coding exons we identified mutations in the CBS genes in 21 of the 22 possible mutant alleles. Ten different missense mutations were identified and one novel splice-site mutation was found. Five of the missense mutations were previously described (G307S, I278T, V320A, T353M, and L101P), while five were novel (A226T, N228S, A231L, D376N, Q526K). Each missense mutation was tested for function by expression in S. cerevisiae and all were found to cause decreased growth rate and to have significantly decreased levels of CBS enzyme activity. The I278T and T353M mutations accounted for 45% of the mutant alleles in this patient cohort. The T353M mutation, found exclusively in four African American patients, was associated with a B(6)-nonresponsive phenotype and detection by newborn screening for hypermethioninemia. The I278T mutation was found exclusively in Caucasian patients and was associated with a B(6)-responsive phenotype. We conclude that these two mutations occurred after ethnic socialization and that the CBS genotype is predictive of phenotype.

Structural analysis and subunit interaction of insulin receptor from membranes of cultured embryonic chick heart cells.

In previous studies of cultured embryonic chick heart, insulin hyperpolarized cells and slowed their beat rate through occupancy of a high affinity receptor. In the present studies, we chemically characterize the native structure and subunit interactions of this insulin receptor. A stokes radius of 87 A and an apparent molecular mass of 350,000 daltons were found for membrane proteins specifically cross-linked to [125I] insulin by disuccinimidyl suberate. A primary subunit of 125,000 daltons in dithiothreitol or 115,000 daltons in its absence (alpha-subunit) was heavily cross-linked. A smaller subunit had a size of 90,000 daltons (beta-subunit). This beta-subunit was not readily labeled by [125I]insulin cross-linking, but insulin enhanced 32P incorporation from [gamma-32P]ATP, enabling its visualization. Subunit interaction could be studied, because alkaline conditions produced dissociation of the native 350,000-dalton receptor. This spontaneous dissociation was not a result of proteolysis and was prevented by acid conditions, oxidants, or N-ethylmaleimide. Using alkaline conditions followed by chemical reduction in two-way gels, we directly visualized the native complex of 350,000 daltons dissociating into combinations of subunits of apparent sizes of 290,000 (alpha 2 beta), 220,000 (alpha alpha), and 195,000 (alpha beta) daltons. Dithiothreitol produced combinations of subunits, which differed from alkaline dissociation. In alkaline conditions, the 290,000 (alpha 2 beta) and 220,000 (alpha alpha) dalton combinations predominated, whereas dithiothreitol produced 190,000 (alpha beta)-dalton proteins, which suggested that alpha-S-S-alpha disulfide bonds existed and were susceptible to chemical reductants, while alpha-S-S-beta disulfide bonds were more sensitive to alkaline lysis. We conclude from these observations that the native insulin receptor of embryonic chick heart cell exists on the sarcolemmal membrane as a relatively homogeneous tetramer of nonhomologous subunits in an alpha 2 beta 2 configuration. The alpha-subunits are the primary sites for insulin binding, and a beta-subunit is autophosphorylated. alpha-S-S-alpha and alpha-S-S-beta bonding exist, and these disulfide bonds have different sensitivities to chemical reducing agents and alkaline lysis.

Evidence supporting a two-receptor model for insulin binding by cultured embryonic heart cells.

Curvilinear Scatchard plots for insulin binding by cultured embryonic heart cells at 15 C were interpreted assuming a two-receptor model (Santora II, A. C., F.B. Wheeler, R.L. DeHaan, and L.J. Elsas II, Endocrinology 104:1059, 1979). The present studies test this hypothesis further. Both 125I-labeled hormone binding and 2-methylamino-[1-14C]isobutyric acid ([14C]meAIB) transport were assayed at 24 C in identical buffers. Equilibrium chicken insulin-binding experiments yielded curvilinear Scatchard functions, consistent with binding to both high affinity, low capacity and low affinity, high capacity receptor sites at 24 C. Insulin-stimulated transport of the model amino acid [14C]meAIB (a specific alanine-preferring system substrate) paralleled the expected occupancy of the low affinity receptors. In competitive binding assays, the abilities of multiplication-stimulating activity (MSA), proinsulin, and insulin to compete for primarily high affinity insulin binding were compared with their abilities to stimulate transport. The relative potencies for binding competition with 34 pM chicken [125I]insulin were insulin greater than proinsulin greater than or equal to MSA (1:0,05:0.03). In contrast, the relative potencies for stimulating [14C]meAIB transport were MSA greater than insulin greater than proinsulin (3:1:0.28). Maximal stimulation of transport by insulin was not additive to that by MSA or proinsulin. The relative potency profile for binding competition with [125I]MSA was the same as that for stimulation of transport: MSA greater than insulin greater than proinsulin (2-3:1:0.2-0.3). Proinsulin, added in excess of insulin at a constant molar ratio, reduced low affinity insulin binding to a greater extent than it reduced high affinity insulin binding. Moreover, the extent of binding to each receptor was predicted from, and thus directly supported, our biological potency data, in which proinsulin was nearly one third as potent as insulin at the low affinity receptor yet possessed only 5% of insulin's potency at the high affinity receptor. The different relative affinity profiles suggest that these two receptors had binding site specificities for different portions of the insulin molecule. Each experiment with proinsulin and insulin in a constant molar ratio was carried out in parallel with an experiment in which insulin was the only unlabeled hormone. Analysis of the results from weighted nonlinear least squares regression fits of data to Michaelis-Menten equations showed that a two-receptor model was necessary to fit the data obtained with insulin as the only unlabeled hormone. Low affinity site binding parameters were also needed when data within each parallel experiment were pooled. The following kinetic experiments indicated the absence of enhanced dissociation of bound [125I]insulin by unlabeled insulin...

Relationship of insulin binding to amino acid transport by cultured 14-day embryonic chick heart cells.

The characteristics of insulin receptors were studied in cultured embryonic chick heart cells which demonstrated insulin-responsive amino acid transport. Binding of [125I]iodoinsulin was time dependent, reversible, saturable, species specific, and proportional to cell number. Optimum binding occurred at pH 7.8 in the presence of 0.1% bovine serum albumin. Curvilinear Scatchard plots were found for chicken and bovine insulin binding at 15 and 30 C. Equilibrium association constants (Kas) and maximum capacities were calculated based on a two-receptor model. When studied at 15 C, chicken insulin was bound with Kas of 5.0 and 0.026 nM-1 for the high and low affinity receptors, respectively. Bovine insulin bound with Kas of 2.1 and 0.03 nM-1. The binding capacities of 600 and 9000 molecules/cell for the high and low affinity receptors, respectively, were the same for both species of ligand. At 30 C, the Ka of the high affinity chicken insulin receptor interaction decreased to 1.6 nM-1, whereas the low affinity Ka was not changed. In competitive binding assays, chicken insulin was 4 and 250 times more potent than bovine and guinea pig insulin, respectively. Human GH and mouse epidermal growth factor did not compete with chicken insulin. Although mouse epidermal growth factor did not compete with insulin, it did stimulate 2-aminoisobutyric acid accumulation. The maximal stimulation by this hormone was less than and additive to that produced by the maximal stimulation of insulin. These data indicate that insulin and epidermal growth factor acted through different receptors to stimulate amino acid transport. When insulin-stimulated functional response was compared to calculated receptor occupancy in this two-receptor model, stimulation of amino acid transport paralleled occupancy of the low affinity receptor such that at half-maximal transport stimulation, approximately 50% of these receptors were occupied. Half-maximal stimulation of 2-aminoisobutyric acid transport occurred at 18- and 20-nM concentrations of bovine and chicken insulins, respectively. Guinea pig insulin failed to stimulate 2-aminoisobutyric acid uptake even at 350 nM. Both the affinity of binding in the low affinity class and the insulin concentration for half-maximal stimulation of 2-aminoisobutyric acid transport were independent of temperature in the temperature ranges studied. We conclude that 14-day embryonic chick heart cells possess at least two classes of receptors which bind insulin. Occupancy of the lower affinity class of insulin receptors correlates quantitatively with insulin stimulation of 2-aminoisobutyric acid transport.

Two mutations in the insulin receptor gene of a patient with leprechaunism: application to prenatal diagnosis.

Leprechaunism is an autosomal recessive disorder caused by mutations in the insulin receptor gene and characterized by intrauterine and postnatal growth restriction, abnormal glucose homeostasis, and severe insulin-resistance. Here we report the biochemical and molecular characterization of a male patient, NZ, who died at 2 yr of age with this syndrome. 125I-Insulin binding to fibroblasts from the proband, his mother, father, and unaffected sister was reduced to 8, 53, 38, and 35% of controls, respectively. Analysis of the insulin receptor gene by polymerase chain reaction amplification using primers flanking each of the 22 exons and direct DNA sequencing identified 2 different mutations in the proband. The paternal mutation was an in-frame deletion of base pairs 1159-1161 in exon 3, which resulted in the loss of the codon for Asn-281. The maternal mutation was a G-->A transition in the first nucleotide of the splice-donor junction in intron 13. The maternal mutation activated a cryptic splice site 27 base pairs upstream in exon 13 and caused an in-frame deletion of amino acids 859-867 of the extracellular domain of the insulin receptor beta subunit. Identification of both mutations enabled prenatal diagnosis in 2 subsequent pregnancies. In the first pregnancy, DNA from cells cultured from chorionic villus (CV) biopsies carried both mutations in the insulin receptor gene. In the second pregnancy, DNA from the CV biopsy cells was negative for both mutations, indicating that the fetus was unaffected by leprechaunism. Insulin binding could not be used in prenatal diagnosis because cells cultured from some control CV biopsies failed to bind insulin. These data indicate that patient NZ with leprechaunism was a compound heterozygote for 2 novel mutations in the insulin receptor gene and that direct DNA sequencing enables prenatal diagnosis for this lethal disorder.

Impaired growth in Rabson-Mendenhall syndrome: lack of effect of growth hormone and insulin-like growth factor-I.

Mutations in the insulin receptor gene cause the severe insulin-resistant syndromes leprechaunism and Rabson-Mendenhall syndrome. There is no accepted therapy for these inherited conditions. Here we report the results of recombinant human GH (rhGH) and recombinant human insulin-like growth factor-I (rhIGF-I) treatment of a male patient, Atl-2, with Rabson-Mendenhall syndrome. The patient was small for gestational age, had premature dentition, absence of sc fat, acanthosis nigricans, fasting hypoglycemia and postprandial hyperglycemia, and extremely high concentrations of circulating insulin (up to 8500 microU/mL). Fibroblasts and lymphoblasts established from this patient had reduced insulin binding, which was 20-30% of the control value. Binding of epidermal growth factor, IGF-I, and GH to the patient's fibroblasts was normal. The growth of fibroblasts cultured from patient Atl-2 in vitro was intermediate between that of fibroblasts from patients with leprechaunism and control values. The patient's growth curve in vivo was far below the fifth percentile despite adequate nutrition. To stimulate growth, therapy with rhGH was initiated, the rationale being to stimulate hepatic IGF-I production and IGF-I receptor signaling, and bypass the inherited block in insulin receptor signaling. Therapy with rhGH (up to 0.5 mg/kg.week) did not improve growth and failed to increase the levels of circulating IGF-I and IGF-binding protein-3 over a 14-month period. As rhGH could not stimulate growth, rhIGF-I (up to 100 micrograms/kg.day) was given by daily sc injection. No increase in growth velocity was observed over a 14-month period. These results indicate that both GH and IGF-I fail to correct growth in a patient with severe inherited insulin resistance. The lack of efficacy of IGF-I treatment may be related to multiple factors, such as the poor metabolic state of the patient, the deficiency of serum carrier protein for IGF-I, an increased clearance of the growth factor, IGF-I resistance in target cells at a receptor or postreceptor level, or an inhibitory action of the mutant insulin receptors on IGF-I receptor signaling.

Application of benefit-to-cost analysis to an X-linked recessive cardiac and humeroperoneal neuromuscular disease.

Benefit-to-cost analysis (using standard economic methods) and the predictive tools of genetics are important in the assessment of genetic services for high burden, single gene disorders. We have studied 6 generations of a 167-member, stable, North Georgia kindred at risk for X-linked recessive humeroperoneal neuromuscular disease with cardiac conduction defects. This disorder began in affected males in the teen years, with total disability expected by the 3rd decade and death by age 50. Using known fecundity rates and Mendelian probabilities, 26.6 heterozygous females and 9.4 hemizygous affected males were expected in the currently developing generation. We compared the compensatory costs for families with affected males against costs of genetic intervention for this disorder. All costs and benefits were discounted to present values at 6% and 10% and a benefit-to-cost ratio was derived. At a 6% discount rate the benefit-to-cost ratio was 21 to 1 while at a 10% discount rate the benefit-to-cost ratio was 14 to 1. We conclude that although this is an unusual X-linked muscular dystrophy, it constitutes a prototypic public and private expense which is largely preventable. The method of cost accounting within pedigrees has wide applicability. The results reemphasize the economic benefit of comprehensive public health programs in genetics, particularly in areas with stable, high risk-populations.

Clinical and biochemical analysis of two families with type I and type II mannosidosis.

We report on two unrelated patients with different presentations of mannosidosis. One patient was affected in early childhood with a severe phenotype characteristic of type I mannosidosis. The other was diagnosed with type II mannosidosis only after the onset of progressive neurologic deterioration in late adulthood. Both were detected by non-invasive urinary screening of oligosaccharides. Lymphoblasts transformed from both patients' blood cells had markedly reduced lysosomal alpha-mannosidase activity. Kinetic analyses showed that alpha-mannosidase from the type I patient had a 400-fold reduction in affinity while that from the type II patient was reduced 40-fold. Lymphoblasts from all 4 parents had reduced alpha-mannosidase activity, but there were overlapping activities among these type I and type II obligate heterozygotes. We conclude that screening urinary oligosaccharides will detect mannosidosis over a wide range of phenotypes, that lymphoblasts transformed from affected heterozygotes have decreased enzymatic activity, and that the severity of clinical expression is related to the degree of enzyme impairment.

Campomelic syndrome and deletion of SOX9.

The human SOX9 gene, located in chromosome region 17q24.1-25.1, encodes a transcription factor involved in chondrogenesis and testis development. Mutations in this gene cause campomelic syndrome (CMPS) with autosomal sex reversal. Here we describe an infant girl with CMPS and an interstitial deletion on the long arm of chromosome 17 (46,X,del(17)(q23.3q24.3). The extent of SOX9 deletion on one chromosome 17 was defined using unique sequence fluorescent in situ hybridization probes. This is the first report of a patient with CMPS bearing a complete deletion of one SOX9 gene, and as such is the strongest evidence to date for dose-dependent action of the SOX9 protein in normal chondrogenesis.

Fine mapping of glycerol kinase deficiency and congenital adrenal hypoplasia within Xp21 on the short arm of the human X chromosome.

We have studied patients with Duchenne muscular dystrophy (DMD), DMD together with glycerol kinase (GK) deficiency, or DMD together with both GK deficiency and congenital adrenal hypoplasia (AHC). Analysis of deletions in these patients allows the mapping of these mutations in Xp21. The following order is proposed: Xpter - L1 - AHC - GK - DMD - Xcen. One of the boys with DMD, GK, and AHC is shown by pulsed-field-gel electrophoresis to have a deletion which has a proximal endpoint at least 500 kb distal from the pERT87 (DXS164) locus.

Verification of the fetal valproate syndrome phenotype.

We have evaluated 19 children who were exposed to valproic acid (VPA) in utero to look for manifestations of a fetal valproate syndrome (FVS), as proposed by Di Liberti et al. [1984]. We found no consistent alterations of pre- or postnatal growth with exposure to VPA monotherapy. Postnatal growth deficiency and microcephaly were present however, in two thirds of children exposed to VPA in combination with other anticonvulsants. Developmental delay or neurologic abnormality was found in 71% of those exposed to VPA monotherapy, and in 90% of those exposed to VPA and other anticonvulsants. Craniofacial anomalies, which can be seen with other anticonvulsant exposures, including midface hypoplasia, short nose with a broad and/or flat bridge, epicanthal folds, minor abnormalities of the ear, philtrum or lip, and micrognathia were also found in infants whose mothers used VPA. Prominent metopic ridge and outer orbital ridge deficiency or bifrontal narrowing and certain major anomalies such as tracheomalacia, talipes equinovarus (with intact spine) and lumbosacral meningomyelocele seem to be peculiar to infants with VPA exposure. Other defects such as urogenital anomalies, inguinal or umbilical hernias, and minor digital anomalies that are common to other prenatal anticonvulsant exposures are also occasionally found in those exposed to VPA. Heart defects have been found in infants exposed to nearly every class of anticonvulsant although the types of defects associated with maternal VPA use may be clarified when classified by pathogenetic mechanism. Our findings overall are in agreement with the report of Di Liberti et al. [1984].

Increased glucose transport by human fibroblasts with a heritable defect in insulin binding.

Insulin and IGF-I binding and their regulation of hexose transport were evaluated in skin fibroblasts cultured from a family (Atl) whose proband had leprechaunism, hypoglycemia, and severe insulin resistance. High affinity insulin binding to proband Atl cells was absent, and partially, but equally, impaired in fibroblasts from his related parents. IGF-I binding to his cultured fibroblasts was within the normal range. Cells from proband Atl had insulin receptor mRNAs similar to control fibroblasts. 3-O-Methyl-D-glucose (OMG) transport by proband Atl was threefold higher than in control fibroblasts (37.7 v 7.6-11 nmol/mL/s) and was insulin-insensitive. Proband Atl fibroblasts had a threefold increase in the Vmax for OMG entry and a concomitant increase in the number of D-glucose-inhibitable cytochalasin B binding sites on their plasma membrane. Similar levels of glucose transporter mRNA were observed in control and proband Atl fibroblasts. These results suggest that fibroblasts from patient Atl have a genetically transmitted mutation in the alpha subunit of their insulin receptor. In the homozygous affected proband, this mutation impairs insulin binding and causes elevated, insulin-insensitive glucose transport. The dysfunction resulting from this mutation is similar to that introduced in Chinese hamster ovary cells by transfection with a truncated alpha subunit.