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Mutations in the GTP-cyclohydrolase I (GCH) gene have been identified as a cause of two disorders: autosomal dominant hereditary progressive dystonia/dopa-responsive dystonia (HPD/DRD) and autosomal recessive GCH-deficient hyperphenylalaninemia (HPA). Detailed clinical descriptions and genetic analysis of patients with phenotypes intermediate between HPD/DRD (mild) and GCH-deficient HPA (severe) have not been reported. We conducted genomic DNA sequencing of the GCH gene in two patients (Cases 1 and 2) manifesting generalized dystonia responsive to levodopa and severe developmental motor delay. In the pedigree of Patient 1, there were HPD/DRD patients in three generations preceding the index case. Patients 1 and 2 were compound heterozygotes with maternally and paternally transmitted mutations in the coding region of the GCH gene. In both compound heterozygotes, tetrahydrobiopterin (BH4) levels in cerebrospinal fluid were lower than those in HPD/DRD. Administration of BH4, in addition to levodopa, further improved the symptomatology of Patient 1. Our data demonstrate a new phenotype of GCH deficiency associated with compound heterozygosity for GCH gene mutations and suggest the usefulness of combined BH4 and levodopa therapy for this disorder.

Disorders of the motor system in children may present acutely or insidiously. The underlying pathologic process may involve the central nervous system or the peripheral nervous system. Some causes of weakness or clumsiness are treatable; others have important prognostic implications for the child. The primary care physician should understand how to take a thorough history and localize the process with the physical and neurologic examination, to decide on further evaluation and management of the child with motor dysfunction.

The Pax-6 gene encodes a DNA-binding transcription factor essential to normal development of the mammalian eye. We have found that in the chick embryo, the Pax-6 gene is first expressed in a crescent-shaped region of future head ectoderm that adjoins the anterior margin of the early neural plate. As development proceeds, this region of Pax-6-positive ectoderm becomes divided into two bilateral domains. Upon contact with the optic vesicles, portions of these domains give rise to the invaginating lens placodes, which contain high levels of Pax-6 mRNA. As with mouse, rat, and zebrafish, chick Pax-6 is also expressed in the neural epithelium of the forebrain and optic vesicles. However, our results indicate that the onset of expression in the prospective head ectoderm occurs at a substantially earlier stage. Experiments involving unilateral ablation of the anterior neural plate indicate that contact with an optic vesicle is not required to maintain expression of Pax-6 in the ectoderm. Experiments in which optic vesicles have been displaced from their normal location further suggest that positioning of Pax-6 domains in the head ectoderm is independent of neighboring optic vesicles. Homozygous defects in the mouse and rat Pax-6 gene are known to cause complete failure of lens formation at the optic vesicle stage and block subsequent development of the optic cup. Our results raise the possibility that Pax-6 may be involved in the early establishment of lens-competent regions within the head ectoderm.

Intramuscular injections of HRP were used to map the spinal cord location of motoneurons innervating wing and shoulder girdle muscles in newly hatched chicks. Motor pools are grouped in the lateral motor column in relationship to embryonic origin of the muscles: muscles derived from the ventral muscle mass are innervated by medially lying motor pools, while muscles derived from the dorsal mass are innervated by lateral pools. Motor pool position is also well correlated with nerve supply. Muscles innervated by nerves diverging from common nerve trunks are innervated by neighboring motor pools. The rostro-caudal organization of the motor pools reflects both proximo-distal and antero-posterior axes of the limb with proximal and anterior muscles innervated from rostral motor pools.

Growth cones are specialized structures that form the distal tips of growing axons. During both normal development of the nervous system and regeneration of injured nerves, growth cones are essential for elongation and guidance of growing axons. Developmental and regenerative axon growth is frequently accompanied by elevated synthesis of a protein designated GAP-43. GAP-43 has now been found to be a major component of growth-cone membranes in developing rat brains. Relative to total protein, GAP-43 is approximately 12 times as abundant in growth-cone membranes as in synaptic membranes from adult brains. Immunohistochemical localization of GAP-43 in frozen sections of developing brain indicates that the protein is specifically associated with neuropil areas containing growth cones and immature synaptic terminals. The results support the proposal that GAP-43 plays a role in axon growth.

Nerve regeneration and developmental outgrowth of axons are both correlated with increased synthesis of an axonal membrane protein designated GAP-43. Phosphorylation of an apparently identical protein, present at lower abundance in adult brains, has been correlated with long-term potentiation, a form of synaptic plasticity. We have now isolated a cDNA clone encoding GAP-43 from neonatal rat brain. The amino acid sequence is extremely hydrophilic, with no potential membrane-spanning domains and no sites for N-linked glycosylation, but with a short hydrophobic segment at the protein's amino terminus, consistent with a model in which GAP-43 extends from the cytoplasmic surface of growth cone and synaptic plasma membranes. Among several tissues and cells examined, GAP-43 mRNA is expressed only in neurons. Developmental and regeneration-associated changes in GAP-43 synthesis appear to be mediated largely at the level of transcription of a single gene.

Development or regeneration of axons in several systems is accompanied by 20-100-fold increases in the synthesis of an acidic, axonally transported membrane protein with an apparent molecular weight of 43-50,000 (Benowitz and Lewis, 1983; Skene and Willard, 1981a, b), which we designate GAP-43. We have proposed that some step(s) in axon growth require production of GAP-43, and perhaps a small number of other "growth-associated proteins," at rates much higher than those typical of mature neurons. This hypothesis predicts that virtually all neurons synthesize GAP-43 at elevated levels during normal CNS development. Here we show that a protein similar to GAP-43 from regenerating toad nerves is prominent among the newly synthesized (35S-methionine-labeled) and total (Coomassie blue-stained) proteins in neonatal rat cerebral cortex and cerebellum, suggesting that synthesis of GAP-43 is indeed a common feature of many developing neurons. Synthesis and accumulation of the protein decline an order of magnitude as animals mature. Antibodies raised against the rat cortex GAP-43 also recognize electrophoretically similar proteins from regenerating toad optic nerves and from developing hamster sensorimotor cortex, indicating that structural features of GAP-43 are conserved in evolution. Cell-free translation of polyadenylated RNA from neonatal and adult cortex suggests that developmental regulation of GAP-43 synthesis is mediated largely through changes in mRNA abundance. These observations together suggest that developmental regulation of GAP-43 gene expression may be common to most vertebrate CNS neurons. GAP-43 remains detectable at a low level in adult rat cortex, and it co-migrates on two-dimensional gels with B-50, a synaptic membrane protein which is a preferred substrate for protein kinase C in adult brains. Phosphorylation of the protein by endogenous kinase(s) in vitro is 4-7-fold greater in growth cone membranes than in mature synaptic membranes, which raises the possibility that local modification of the protein in axon terminals may be synergistic with regulation of GAP-43 synthesis in the cell body.