Detailed studies of growth hormone secretion in cystinosis patients.

Background: Cystinosis is an autosomal recessive disorder characterized by intralysosomal cystine accumulation. Growth retardation is more pronounced in cystinosis than in other chronic kidney diseases and is mostly not corrected by cysteamine.

Methods: Growth was evaluated in nine cystinosis patients, all treated with cysteamine, both after cysteamine and recombinant human growth hormone (rhGH) therapy initiation. Growth hormone (GH) secretion was studied by nocturnal GH measurements in four of nine patients and by glucagon test in four of nine patients.

Results: RhGH was administered to seven of nine patients. At rhGH initiation, height was below -2 SDS in five of seven patients, final height was above -2 SDS in six of seven. In two patients not treated with rhGH, final height remained below -4 SDS despite cysteamine treatment being started at the age of 6.1 and 8.1 years, respectively. Nocturnal GH secretion was normal in all patients. Glucagon tests revealed GH deficiency in one patient; two of four patients had abnormal GH peak timing.

Conclusions: We present the first reported case of GH deficiency in cystinosis. Although no overt GH deficiency was detected in other patients, abnormal GH peak timing can indicate a subclinical GH secretion problem. RhGH significantly improved growth in cystinosis patients and should be initiated early in life.