Galactose is an important constituent

Galactose is an important constituent of the complex polysaccharides which are part of cell glycoconjugates, key elements of immunologic determinants, hormones, cell membranes structures, endogenous animal lectins, and numerous other glycoproteins. In addition galactose is incorporated in galactolipids, important structure elements of the central nervous system. It is not difficult to assume that the abnormal galactose metabolism in galactosemic patients could have profound and widespread effects on glycoconjugate structures and their biological function. Classically, the term 'galactosemia' was associated with an inherited disorder of galactose utilization characterized by malnutrition, liver disease, cataracts, and mental retardation, resulting from the specific deficiency of galactose-1-phosphate uridyltransferase. However, other enzymatic defects with variations of clinical presentation can also lead to galactosemia. Thus it is preferably better to refer to these abnormalities of metabolism by the specific enzymatic deficiencies which are described below. Transferase deficiency Failure to thrive is the most common initial clinical sign of galactose- 1-phosphate uridyltransferase deficiency, and it is present in all cases. Vomiting or diarrhea is present in almost all patients, usually starting within a few days of milk ingestion. Jaundice, hepatomegaly, or both are present almost as frequently after the first week of life. The jaundice of intrinsic liver disease may be accentuated by severe hemolysis in some patients. Abnormal liver function tests and ascites may develop. The reason for liver toxicity remains obscure. The liver of affected patients has a characteristic acinar formation, and liver biopsy on occasion has been helpful in establishing the diagnosis. There is high frequency of neonatal death due to Escherichia coli sepsis, possibly caused by the inhibition of leucocyte bactericidal activity. Galactose 1-phosphate and galactitol have been detected in the kidneys of patients with galactosemia. Renal toxicity may manifest as renal tubular dysfunction and a defect in urine acidification mechanisms. Galactosuria, hyperchloremic acidosis, albuminuria, and aminoaciduria may also occur. Hyperchloremic acidosis could be also secondary to the gastrointestinal disturbance and poor food intake. Galactosuria may be intermittent, depending on oral intake, and can disappear within 3-4 days with the use of intravenous glucose. The finding of urinary reducing substances which do not react in a glucose oxidase test should raise the suspicion of galactosemia. This finding, however, does not establish the diagnosis, since galactosuria can also occur in intestinal lactase deficiency and in severe liver disease due to other causes. Ovarian atrophy appears to be an important manifestation of galactose toxicity, with clinical and biochemical evidence of ovarian dysfunction present in nearly all affected females. The basis of the toxicity has not been defined. The consequences of the gonadal dysfunction range from failure of pubertal development, through primary amenorrhea to secondary amenorrhea or premature menopause (75-76% of affected females). Although gonadal function has been described as early as infancy based on elevations of follicle stimulating hormones (FSH) and abnormal stimulation testing, no predisposing factor for gonadal dysfunction can be found. Previous recommendations that dietary lactose restriction from birth may be beneficial have in fact not prevented gonadal dysfunction. In the galactosemic male, a complete understanding of gonadal dysfunction has not yet been described. The majority- but not all-of male galactosemic patients had normal pubertal development, and a few individuals have been found to have normal semen. Cataracts have been observed within a few days of birth. These may be found only on slit-lamp examination and can be missed with an ophthalmoscope, since they consist of punctate lesions in the fetal lens nucleus. Several hypotheses have been postulated to account for their formation and are mentioned above. It seems conclusive that the initiator of the process in rats is galactitol and not galactose 1-phosphate. Galactose 1-phosphate accumulates only late in the process and is absent in patients with galactokinase deficiency who present with cataracts. Development of mental retardation may be apparent after the first months of life. Signs of increased intracranial pressure and cerebral oedema have been observed as a presenting feature. Many of the toxicity symptoms can rapidly resolve with institution of dietary lactose restriction. However, a substantial percentage of children have subnormal IQs and speech and language deficits, but rarely devastating neurological sequelae. Most galactosemic patients with lactose restriction are deficient of cognitive functioning in one or more areas. The deficits are variable and do not appear to be related to the age, diagnosis, or the severity of illness at presentation. The pathophysiology of these impairments in galactosemia remains unknown. Several hypotheses are suggested, including toxic oedema due to increased brain galactitol concentrations, changes in the second messenger pathway, and changes of the energy status of the brain.
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