Milacemide treatment in mice enhances acquisition of a Morris-type water maze task.

The N-methyl-D-aspartate (NMDA) subtype of the glutamate receptor appears to be involved with processes of learning and memory. A neutral amino acid binding site is known to exist on the NMDA complex. Glycine binds with high affinity to this site and has been found to potentiate NMDA activity. 2-N-Pentylaminoacetamide HCl (milacemide) is a glycine agonist that has been found to enhance performance of rodents in passive and active avoidance tasks and has improved the performance of humans in several word retrieval tasks. We evaluated the effects of milacemide on the performance of male C57BL/6J mice in a complex spatial task, the Morris water maze. Because NMDA receptor activation appears involved in induction of long-term potentiation, it was hypothesized that milacemide administration would be involved in task acquisition. Therefore, mice were treated with either milacemide (10 mg/kg) or vehicle 1 h prior to training on each of 4 consecutive days. Results indicated that mice treated with milacemide learned the task significantly faster than controls over 4 days of training, as measured by mean distance (cm) to reach the goal platform. Therefore, agonism of the glycine site on the NMDA receptor appears to facilitate performance of learning in a spatial memory task.

Analysis of the chondroitin sulfate proteoglycan core protein (CSPGCP) gene in achondroplasia and pseudoachondroplasia.

Achondroplasia and pseudoachondroplasia are autosomal dominant skeletal dysplasias resulting in short-limbed dwarfism. Histologic and ultrastructural studies of the cartilage in pseudoachondroplasia and in homozygous achondroplasia have suggested a structural abnormality in chondroitin sulfate proteoglycan (CSPG), a major structural protein in the extra-cellular matrix. The gene encoding CSPG core protein (CSPGCP) is thus a logical "candidate gene" for analysis in these conditions. cDNA probes encoding CSPGCP were used to identify restriction fragment length polymorphisms (RFLPs) in DNA from a panel of control individuals. No gross alterations at the CSPGCP locus were noted in DNA from 37 individuals with achondroplasia and 5 individuals with pseudoachondroplasia. In addition, allelic frequencies of the RFLPs were not significantly different among controls and patients with either condition. In one three-generation family with achondroplasia, close linkage of the CSPGCP locus and the skeletal dysplasia was excluded using a Bgl II polymorphism. Similarly, in a three-generation family with pseudoachondroplasia, the CSPGCP gene was not tightly linked to the disease phenotype. These results indicate that mutations at the chondroitin sulfate proteoglycan core protein locus do not cause achondroplasia or pseudoachondroplasia in these families.

Late-onset ornithine transcarbamylase deficiency in male patients.

We report on 21 male patients who presented after 28 days of age with ornithine transcarbamylase (OTC) deficiency, which we define as late-onset OTC deficiency. These patients appeared normal at birth, but irritability, vomiting, and lethargy, which were often episodic, later developed. The age at presentation ranged from 2 months to 44 years. Biochemical testing revealed hyperammonemia, hyperglutaminemia, hypocitrullinemia, increased urinary orotate excretion, and decreased liver OTC activity measured in vitro, which ranged from 0% to 15% of normal. Male patients who were older at presentation had a somewhat different pattern of presenting symptoms and were more likely to die. These data illustrate the phenotypic variability of OTC deficiency. Unexplained episodes of repetitive or protracted vomiting in association with progressive alterations in behavior or neurologic findings should suggest the diagnosis of a urea cycle defect (or another symptomatic inborn error of metabolism), regardless of the age or medical history of the patient.

Use of denaturing gradient gel electrophoresis for detection of mutation and prospective diagnosis in late onset ornithine transcarbamylase deficiency.

Ornithine transcarbamylase (ornithine carbamoyltransferase, EC 2.1.3.3) deficiency is an X-linked inborn error of metabolism with considerable phenotypic variability in affected males. Using a combination of the polymerase chain reaction and denaturing gradient gel electrophoresis (DGGE), we defined a mutation in a family in whom affected males have significant residual enzyme activity. A C----T change in the first nucleotide of codon 277 resulted in the substitution of a tryptophan for an arginine at amino acid 245 of the mature protein. This change appears to represent a deleterious mutation rather than a polymorphism on the basis of several factors: the change occurs at a highly conserved arginine residue, significant size and change differences exist between arginine and tryptophan, and this change was not seen on DGGE screening of 26 unrelated individuals representing 43 chromosomes. Diagnosis of an at-risk male newborn in this family was performed using direct mutational analysis. In families with partial enzyme deficiencies in whom biochemical data may be difficult to evaluate, direct detection of mutations at the OTC locus permits definitive diagnosis. This represents the first description of a mutation in late onset OTC deficiency and demonstrates direct mutational analysis by DGGE for prospective diagnosis in a genetic disorder.

Allopurinol-induced orotidinuria. A test for mutations at the ornithine carbamoyltransferase locus in women.

Ornithine carbamoyltransferase is an X-linked mitochondrial enzyme expressed in hepatocytes and enterocytes. A deficiency of this enzyme results in central nervous system dysfunction, which may be fatal in newborn boys. Milder forms are seen in older boys and girls and in adults. Establishing the carrier status of women at risk for ornithine carbamoyltransferase deficiency is important for determining reproductive and medical risks for affected women. We report a test to establish the carrier status of women at risk for ornithine carbamoyltransferase deficiency. This test relies on the allopurinol-induced accumulation of orotidine, whose synthesis is stimulated by carbamoyl phosphate, a substrate that accumulates in ornithine carbamoyltransferase deficiency. We used anion-exchange, high-performance liquid chromatography to measure urinary orotidine and orotic acid excretion after the administration of a 300-mg oral dose of allopurinol in 25 [corrected] women who were obligate heterozygotes, 13 who were probable heterozygotes, 15 mothers of affected boys from monoplex families (families with only one affected member), 12 mothers of affected girls from monoplex families, and 21 [corrected] normal, unrelated women who were not carriers. Urinary orotidine excretion was increased 3 SD or more above the mean value for the normal women in 95.8 percent of the obligate heterozygotes, 84.6 percent of the probable heterozygotes, 73.3 percent of the mothers of affected boys in monoplex families, and 33.3 percent of the mothers of affected girls in monoplex families, thus establishing that these women were carriers of a mutant ornithine carbamoyltransferase allele. The presence of allopurinol-induced orotic aciduria was not as sensitive or specific an indicator of carrier status as the presence of orotidinuria. We conclude that measurement of urinary orotidine excretion after the administration of allopurinol is a simple and reliable test for the identification of women who are heterozygous for ornithine carbamoyltransferase deficiency.