There is currently no international consensus on the definition of mild HPA, however, it is most frequently diagnosed at blood Phe levels between 2–6 mg/dL.Phenylalanine is a large, neutral amino acid (LNAA). LNAAs compete for transport across the blood–brain barrier (BBB) via the large neutral amino acid transporter (LNAAT). If phenylalanine is in excess in the blood, it will saturate the transporter. Excessive levels of phenylalanine tend to decrease the levels of other LNAAs in the brain. As these amino acids are necessary for protein and neurotransmitter synthesis, Phe buildup hinders the development of the brain, causing intellectual disability.Recent research suggests that neurocognitive, psychosocial, quality of life, growth, nutrition, bone pathology are slightly suboptimal even for patients who are treated and maintain their Phe levels in the target range, if their diet is not supplemented with other amino acids.Classic PKU affects myelination and white matter tracts in untreated infants; this may be one major cause of neurological problems associated with phenylketonuria. Differences in white matter development are observable with magnetic resonance imaging. Abnormalities in gray matter can also be detected, particularly in the motor and pre-motor cortex, thalamus and the hippocampus.It was recently suggested that PKU may resemble amyloid diseases, such as Alzheimers disease and Parkinsons disease, due to the formation of toxic amyloid-like assemblies of phenylalanine. Tetrahydrobiopterin-deficient hyperphenylalaninemia
A rarer form of hyperphenylalaninemia is tetrahydrobiopterin deficiency, which occurs when the PAH enzyme is normal, and a defect is found in the biosynthesis or recycling of the cofactor tetrahydrobiopterin (BH4).
The symptoms of nutcracker esophagus are intermittent, and may occur with or without food. Rarely, patients can present with a sudden obstruction of the esophagus after eating food (termed a food bolus obstruction, or the steakhouse syndrome) requiring urgent treatment. The disorder does not progress to produce worsening symptoms or complications, unlike other motility disorders (such as achalasia) or anatomical abnormalities of the esophagus (such as peptic strictures or esophageal cancer). Many patients with nutcracker esophagus do not have any symptoms at all, as esophageal manometry studies done on patients without symptoms may show the same motility findings as nutcracker esophagus. Nutcracker esophagus may also be associated with metabolic syndrome. The incidence of nutcracker esophagus in all patients is uncertain. Pathophysiology
Pathology specimens of the esophagus in patients with nutcracker esophagus show no significant abnormality, unlike patients with achalasia, where destruction of the Auerbachs plexus is seen. The pathophysiology of nutcracker esophagus may be related to abnormalities in neurotransmitters or other mediators in the distal esophagus. Abnormalities in nitric oxide levels, which have been seen in achalasia, are postulated as the primary abnormality. As GERD is associated with nutcracker esophagus, the alterations in nitric oxide and other released chemicals may be in response to reflux. Diagnosis
In patients who have dysphagia, testing may first be done to exclude an anatomical cause of dysphagia, such as distortion of the anatomy of the esophagus. This usually includes visualization of the esophagus with an endoscope, and can also include barium swallow X-rays of the esophagus.