Information researched by Crystal's neurologist from Dr. Richard Kelley!

Diet for SMA

Although there are some distinct abnormalities of fatty acid metabolism in SMA (see Crawford et al. Abnormal fatty acid metabolism in childhood spinal muscular atrophy, Ann Neurol 1999; 45: 337-343), the abnormalities do not rise to the same level of clinical significance as they do in primary defects of fatty acid beta-oxidation, such as MCAD deficiency or LCHAD deficiency in children or CPT deficiency in adults. Children with SMA (both "acute" infantile and chronic forms) appear to have reduced ketogenesis plus abnormalities in their free fatty acid profiles that indicate a relative block in fatty acid uptake by mitochondria. Based on studies of plasma fatty acid and acylcamitine levels, this apparent block in fatty acid catabolism probably precedes CPT-l. Despite these abnormalities, most older children with SMA when sufficiently fasted can mount a moderately good ketosis, which indicates that the impaired fatty acid metabolism is perhaps greater in muscle than it is in liver. Although the fatty acid handling problem of SMA itself recommends certain dietary practices, such as limitation of fat as a percentage of calories, the dietary management of SMA in most respects is no different from that of any child with markedly reduced muscle mass. That is, because muscle is the most important nutritional reserve in the body and, when needed, supplies substrate to the rest of the body for protein synthesis and gluconeogenesis, the greatly reduced size of this amino acid reservoir has important effects on overall nutrition in children with SMA. 1. Muscle protein turnover--with simultaneous uptake and release of amino acids to plasma--is a continuous process with net uptake of amino acids in postprandial periods and net loss of muscle protein during fasting periods. Liver also can "store" protein in this manner, but the liver also is the site of much net catabolism of amino acids. Following a meal, the reduced muscle mass in SMA limits the systemic ability to take up diet-derived amino acids for conversion into protein, so that relatively larger amounts of amino acids are catabolized by liver and other tissues that have a more limited ability to "store" protein. During fasting, a larger fraction of body muscle of an SMA child must be catabolized to supply amino acids for gluconeogenesis. In the competition between these two phenomena, catabolism often wins out and progressive muscle wasting occurs. 2. During fasting, the plasma amino acid levels in children with SMA fall in just 4 hours after a meal to the same "catabolic" levels that are not reached until 8 hours after a meal i a child with normal musculature. Therefore, children with SMA should have more frequent meals or protein-containing snacks during the day and, if sleeping for more than 8 hours at night, should be given cornstarch at bedtime (0.5-1g/kg) to limit overnight fasting and muscle protein catabolism. Overall protein intake should be generous (1.5 to 2 g/kg/d), but only if frequent feedings are given. Much greater amounts of protein have been given to SMA children, but the resulting higher amino acid levels can become toxic (e.g., arrhythmias) in the immediate postprandial period. Following these principles of protein nutrition often eliminates the cyclic vomiting that is common in SMA. 3. In that fat is the preferred fuel of muscle, and because most dietary fat is metabolized by muscle (except with fasting and ketogenic diets), the amount of fat in the diet should be reduced more or less in proportion to the degree that the muscle mass is reduced, allowing for the required 3-5% of calories as essential fatty acids. 4. Because of the loss of muscle, which has a very high metabolic rate per gm of tissue, and because of the underutilization of the muscle that remains, caloric requirements per kg body weight are much lower than predicted by age and weight, often 20 to 30% lower or more. K cal/kg must be individualized to give a normal rate of weight gain. For infants with SMA, the process of neurogenic muscle wasting in the acute phase occasionally may equal weight gain associated with linear growth giving a static weight and the appearance of failure-to-thrive. 5. Weight-for-height percentiles are almost meaningless when applied to SMA. The well-nourished child with SMA often is at or below the 3rd centile of weight for height. Subcutaneous fat thickness is a better gauge. In general, the weight in standard deviations from the mean should be 1 to 2 SD below that of length. A child with SMA who doesn't look at least somewhat skinny may be "overweight" On the other hand, less active SMA children benefit from some excess adipose tissue to provide a better cushion against decubiti. There has also been some discussion as well as a few informal trials with amino acid supplements, such as glutamine and arginine, which may indeed have a role in the treatment of SMA, but these should still be viewed as experimental. Many parents believe their SMA children are stronger when given elemental formulas, such as Neocate or Tolerex, but such an effect is not proven. Richard Kelley.

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