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Another form of nontraditional inheritance involves the DNA found in the mitochondria, instead of the nucleus. The mitochondrial chromosome is circular, and contains no introns, very little noncoding DNA, and only a small number (16,569:Coreg) of base pairs compared with nuclear DNA (50). Its genetic code is different from that seen in the nucleus. Because the ova, but not the sperm, contain mitochondria, conditions inherited in this manner have a unique pattern of inheritance.

Although not directly related to fluid and electrolyte management, acidв base disorders are important to consider in the care of surgical infants and children because shifts in hydrogen or bicarbonate will effect distribution and total body content of the major electrolytes. Acid base disorders are termed either metabolic or respiratory, based on the pathogenesis of the imbalance. Metabolic acidosis is either from excess acid production or administration, or renal losses of bicarbonate. Metabolic alkalosis is usually from volume contraction or loss of hydrogen ions. Respiratory acidosis results from carbon dioxide retention, whereas alkalosis is the consequence of hyperventilation. Disorders are termed simple if there is only one primary disorder, or mixed if two or more are involved. The body attempts to correct metabolic disorders in the short term by altering respiration; however, respiratory defects can only be compensated by metabolic processes over longer periods of time. Compensatory mechanisms never overcorrect the primary derangement.

Metabolic acidosis occurs when exogenous acid is administered, endogenous acids are produced, or bicarbonate is lost in either gastrointestinal fluid or in the urine. It is defined by a plasma pH less than 7.35. The body attempts to compensate by increasing minute ventilation in an effort to lower dissolved carbon dioxide content. There are two major types of metabolic acidosis, anion gap and nonanion gap acidosis. The anion gap is the difference between unmeasured cations and anions and is usually around 8 to 16 meq per L. It is estimated by the formula:

Anion gap (meq/L) = sodium concentration - (chloride + bicarbonate concentrations)

When the calculated gap is in the normal range, it is termed nonanion gap acidosis, which is usually related to bicarbonate loss. If the anion gap is above the normal range, it is due to excess acid production or administration.

In an autosomal (non“sex-linked) dominant (AD) condition, an abnormality in one member of a gene pair is sufficient to cause the condition. Although the strict definition of a dominant condition specifies that the heterozygous individual is indistinguishable from the homozygous-affected individual, this is often not the case. Instead, frequently the homozygote is more severely affected than the heterozygote.

Most dominant conditions involve the formation of structural proteins. Changes in one gene of a pair can result in a phenotype through loss of function, where the abnormal gene produces an absent gene product. Because only one of the pair of genes is working properly, only half of the normal amount of product is formed. Another way that a dominant gene can cause a genetic condition is through a gain of function, where the new protein takes on a deleterious function (9).

Individuals with a dominant condition have a 50% risk of passing the condition on to their offspring, and males and females are affected with equal frequency. Patients with AD conditions often have other affected family members. Families in which an AD condition is segregating often show a vertical pattern of transmission, with multiple generations affected (Fig. 2-1). Because dominant conditions have a wide variability in expression, a parent might not be identified as having the condition unless he or she is carefully examined for minor manifestations. In some cases, neither parent is affected and the child is a new mutation. The frequency of these new mutations increases with increasing paternal age. Rarely, an individual in an autosomal dominant pedigree who must be a carrier of the gene based on the inheritance pattern shows no manifestations. This is termed incomplete penetrance.

An example of a common AD condition is neurofibromatosis 1 (NF1) (MIM 162200), which occurs in 1 in 3,000 births.