Neuronal-Axonal Disease Not Associated with Werdnig-Hoffmann Disease
Neuronal-axonal disease not associated with Werdnig-Hoffmann disease is a rare condition that primarly involves the axons. Neuronal-axonal disease not associated with Werdnig-Hoffmann disease refers to a group of peripheral neuropathies in which the axon is the primary structure involved. Nerve conduction is normal or only moderately slow. It is diagnosed by sural nerve biopsy. The biopsy shows sphered bodies in the axons, particularly in the presynaptic region. It is important to diagnose this entity because neonates with this disorder may not deteriorate and may even improve with time. The disease has a sporadic or autosomal-dominant inheritance.

Giant Axonal Neuropathy
Giant axonal neuropathy is a rare condition that involves the central and peripheral nervous systems. It should be suspected when the patient has tightly curled, kinky, poorly pigmented scalp hair. Motor and sensory nerve conduction velocity may not be decreased. The diagnosis is established by finding greatly enlarged axons filled with disarrayed neurofilaments in sural nerve biopsy. The cause is probably an error of metabolism affecting the formation of neurofilaments.

Infantile Porphyria
Infantile porphyria may produce neonatal hypotonia. The clinical course is characterized by recurrent polyneuropathy. Nerve conduction velocity is normal. The characteristic findings are increased urine delta-aminolevulinic acid and coproporphyrin levels and decreased erythrocyte aminolevulinic acid synthetase activity.

Congenital sensory neuropathy with anhidrosis
Congenital sensory neuropathy with anhidrosis may produce neonatal hypotonia. It should be suspected in hypotonic neonates with anhidrosis, no tears, and episodes of unexplained fever. Nerve conduction velocity is normal. Autonomic dysfunction is present. Evidence of autonomic dysfunction can be proven by intracutaneous injection of 0.01 mL of histamine phosphate (1:10,000) and installation of 2.5% methacholine into the conjunctival sac. In a patient with normal autonomic function, the intracutaneous injection of histamine produces a wheal with surrounding erythema, and the installation of diluted methacholine into the conjunctiva sac does not produce miosis. In neonates with autonomic dysfunction, the intracutaneous injection of histamine produces a wheal with a surrounding erythema and the installation of diluted methacholine into the conjunctival sac evokes a rapid miosis. The diagnosis is established by sural biopsy. Sural biopsy in patients with congenital sensory neuropathy with anhidrosis shows a reduction or absence of small myelinated and unmyelinated fibers.

Riley-Day syndrome
Riley-Day syndrome or familial dysautonomia may produce neonatal hypotonia. It should be suspected in hypotonic neonates of Ashkenazi Jewish parents with episodes of unexplained fevers or hypothermia, excessive sweating, and irritability. Fungiform papillae are absent. Abnormal rolling tongue movements, retrocollis, and opisthotonus are usually present. There is no response to pain, and corneal responses and deep tendon reflexes are absent. Sensory nerve action potentials are absent. Evidence of autonomic dysfunction can be proven by intracutaneous injection of 0.01 mL of histamine phosphate (1:10,000) and installation of 2.5% methacholine into the conjunctival sac. In neonates with normal autonomic function, the intracutaneous injection of histamine produces a wheal with surrounding erythema, and the installation of diluted methacholine into the conjunctiva sac does not produce miosis. In neonates with autonomic dysfunction, the intracutaneous injection of histamine produces a wheal with a surrounding erythema and the installation of diluted methacholine into the conjunctiva sac evokes a rapid miosis. The diagnosis is established by DNA testing. In the past, the diagnosis was established by the combination of ancestry, excessive sweating, and sural biopsy. Sural biopsy in patients with Riley-Day syndrome shows a reduction or absence of small myelinated and unmyelinated fibers.