Congenital cholinesterase deficiency (succinylcholine apnea). Cholinesterase is an enzyme best known for its role in regulation of nerve impulse transmission via breakdown of acetylcholine at the nerve synapse and neuromuscular junction. There are two categories of cholinesterase: acetylcholinesterase (“true cholinesterase”), found in RBCs and nerve tissue; and serum cholinesterase (“pseudocholinesterase”). Cholinesterase deficiency became important when […]
Cystic fibrosis. Cystic fibrosis (mucoviscidosis, or fibrocystic disease of the pancreas) is the most common eventually lethal autosomal recessive inherited disorder in Europeans (estimated gene frequency of 1 in 2,000 live births). Incidence in African Americans is 2% of that in Europeans; it is rare in Asians. About 90% of homozygotes have symptoms resulting predominately […]
Wilson’s disease (hepatolenticular degeneration). Wilson’s disease is a familial disorder of copper metabolism transmitted as an autosomal recessive trait. It most often becomes manifest between ages 8 and 30 years; symptoms usually do not develop before age 6 years. About 30%-50% of patients initially develop hepatic symptoms, about 30%-40% begin with neurologic symptoms, and about […]
Several well-known disorders affecting skeletal muscle either are not congenital or do not yet have any conspicuously useful laboratory test. Among these are disorders whose primary defect is located in the central nervous system or peripheral nervous system rather than in skeletal muscle itself. In this group are various neurologic diseases that secondarily result in […]
Chromosome analysis. There are several conditions, some relatively common and some rare, that result from either abnormal numbers of chromosomes, defects in size or configuration of certain single chromosomes, or abnormal composition of the chromosome group that determines sexual characteristics. Laboratory diagnosis, at present, takes three forms. First, chromosome charts may be prepared on any […]
Primary (metabolic) aminoacidopathies Phenylketonuria (PKU). Classic PKU is inherited as an autosomal recessive trait. It is uncommon in Asians and African Americans and is due to deficiency of a liver enzyme known as “phenylalanine hydroxylase,” which is needed to convert the amino acid phenylalanine to tyrosine. With its major utilization pathway blocked, phenylalanine accumulates in […]
The best known of this group are Hunter’s and Hurler’s syndromes. In these conditions there is inability to metabolize certain mucopolysaccharides, resulting in accumulation and storage of these substances in various body organs and tissues and excretion of some stored material in the urine. Hurler’s syndrome. Hurler’s syndrome is caused by deficiency of the enzyme […]
Lysosomal storage diseases are the result of genetic deficiency in certain enzymes found in tissue cell cytoplasmic lysosomes. These enzymes help metabolize certain glycoproteins, glycolipids, and mucopolysaccharides. The substance normally altered by the deficient enzyme accumulates in the cell lysosome area, and a storage disease results. The nonmetabolized substance either is stored in the tissue […]
Galactosemia. Galactosemia results from congenital inability to metabolize galactose to glucose. The most common source of galactose is milk, which contains lactose. Lactose is converted to glucose and galactose in the gastrointestinal (GI) tract by the enzyme lactase. There are three forms of galactosemia, each with autosomal recessive inheritance, and each caused by an enzyme […]
Various diagnostic modalities are available. Some genetic disorders involve chromosomes. Many chromosomal abnormalities are autosomal (not involving the sex chromosome); others are sex-linked (inherited through the sex chromosomes). In some cases there may be total or partial deletion of a chromosome, presence of an extra chromosome attached to a chromosome pair (trisomy), or translocation, when […]
