Chapter 38 - Primary Metabolic and Renal Hyperuricemia

Abstract

This chapter focuses on purine metabolism and the purine metabolic enzyme disorders, Lesch-Nyhan syndrome and pyrophosphate synthetase (PRPS) superactivity. It also discusses other single gene disorders such as glycogen storage disease types I and VII and the underexcretion type hyperuricemia, familial juvenile hyperuricemic nephropathy. Renal underexcretion is the main mechanism for the development of primary hyperuricemia in most patients, even in the overproduction type patients without genetic disorders. Lesch-Nyhan disease is the most common cause of hyperuricemia in infancy and childhood and the frequency approximates one in 3,80,000 births. The clinical manifestations of Lesch-Nyhan disease include urolithiasis or gout due to uric acid overproduction and overexcretion, mental and growth retardation, choreoathetosis, dystonia, compulsive self-injurious behavior, and sometimes, megaloblastic anemia. Infants with Lesch-Nyhan disease appear normal at birth and usually develop normally for the first 3-8 months. The majority of patients with Lesch-Nyhan disease are recognized when they are between 3 and 12 months of age with motor disability or hypotonia. Extrapyramidal signs such as choreoathetosis and dystonia and pyramidal signs such as hyperreflexia and extensor plantar reflex typically begin to develop between 1 and 2 years of age. PRPS overactivity is an X-linked recessive disorder and only a small number of point mutations in PRPSl have been identified in patients with PRPS overactivity. The clinical manifestations of PRPS overactivity include urolithiasis or gout due to hyperuricemia and hyperuricosuria similar to HPRT deficiency, and neurological deficits frequently including sensorineural deafness.Patients with the greater severity show symptoms such as sensorineural deafness, cerebellar ataxia, muscular hypotonia, mental and motor retardation since early childhood, and signs of uric acid overproduction.