Tyrosinemia Type 1: An Overview of Nursing Care

Elizabeth Barnby, DNP, ACNP-BC, RN

Disclosures

Pediatr Nurs. 2014;40(2):61-66. 

In This Article

Diet and Pharmacotherapy

TT1 is a treatable disease. An experienced team that includes a dietician, medical geneticist, advanc ed practice nurse, psychologist, school nurse liaison, and other practitioners will need to collaborate as an interdisciplinary team to enhance outcomes (Paradis, 1996). The treatment includes a low-protein diet with medical food or formula, as well as the medication nitisinone (Orfadin®). The orphan drug nitisinone is used to treat TT1. Nitisinone shifts the metabolic pathway for the catabolism of tyrosine (El-Karaksy et al., 2010). The recommended 1 to 2 mg/kg/day is divided into two daily doses and should be titrated until succinylacetone is undetected in the urine (Al-Dhalimy, Overturf, Finegold, & Grompe, 2002; D'Eufemia, Celli, Tetti, & Finocchiaro, 2011; McKiernan, 2006). It must be taken at least one hour before or two hours after a meal to promote complete absorption because food effect is unknown. It is available in 2, 5, and 10 mg capsules. For children unable to swallow capsules, the capsules can be opened and the contents suspended in a small amount of water, formula, or apple sauce immediately before use ("Nitisinone: New Drug…," 2002).

One side effect of nitisinone observed during clinical trials was photophobia (eye irritation) related to elevated tyrosine levels. It is essential that the child remain on a low protein diet while taking nitisinone to prevent this complication (Kamboj, 2008; "Nitisinone: New Drug…," 2002; Smith, 2008). Specific dietary recommendations are based on phenylalanine and tyrosine levels. The goal is to maintain serum phenylalanine above 20 to 30 μmole/L and serum tyrosine between 200 to 500 μM to prevent corneal opacities and cognitive delays (Scott et al., 2008). Medical food and supplemental low-protein foods can be ordered online with the assistance of a certified dietician who specializes in the management of children with inborn errors of metabolism. However, these foods are not always covered by health insurance plans (see Table 2). Chemistry scales for weighing medical food and low-protein cookbooks are also available from these companies.

Corneal opacities have been known to develop in some children taking nitisinone for TT1. It is highly recommended that plasma tyrosine levels be measured frequently, and slit lamp ophthalmology examinations performed yearly (Ahmad, Teckman, & Lueder, 2002). Corneal opacities have been associated with high plasma tyrosine levels; however, it is unclear if other factors may also contribute to this problem (Lock, Gaskin, Ellis, Provan, & Smith, 2006). To prevent this complication, tyrosine levels should be kept below 500 μM.

Yearly electrocardiograms to moni tor for interventricular septal hypertrophy and signs of cardiomyopathy are advised. This is a rare complication seen in some children with TT1. If signs of cardiomyopathy are detected, referral to a pediatric cardiologist is advised. Children treated early with nitisinone are less likely to develop cardiomyopathy (Arora, Stumper, Wright, Kelly, & McKiernan, 2006).

Tyrosine is also metabolized within the kidneys. Consultation with a pediatric nephrologist to monitor signs of tubular injury with resulting Fanconi syndrome is prudent. There is increased risk of renal carcinoma related to toxic metabolites. Nitisinone can decrease progression of renal disease (Santra, Preece, Hulton, & McKiernan, 2008). Measurement of cystatin C is a better indicator of renal function in the pediatric population (Westhuyzen, 2006). Growth delays and vitamin D-resistant rickets related to renal disease are common and usually improve with nitisinone therapy (Parri et al., 2006).

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