Nephrolithiasis in identical twins: the impact of nature vs nurture.
OBJECTIVE
To assess possible underlying metabolic abnormalities in three sets of monozygotic twins, to evaluate the interplay among the factors of kidney stone formation, a complex multifactorial process influenced by environmental, genetic and anatomical factors.


METHODS
Three sets of identical twins with either cystine or calcium oxalate stones were identified. Demographic data, medical histories and the results of 24-h urine testing, with samples collected on self-selected diets, were reviewed and analysed.


RESULTS
The cystinuric twins had very similar cystine excretion rates, while stone activity was significantly more pronounced in one. Metabolic abnormalities were concordant in one set of twins with calcium oxalate stones, both being hypercalciuric and hyperuricosuric. However, metabolic abnormalities were discordant in the other pair, one twin with hypercalciuria and the other with hypocitraturia. Two of the three pairs had low urinary volume.


CONCLUSIONS
These results support previous observations that environmental, genetic and potentially, anatomical factors play roles in kidney-stone formation. Additional controlled studies of monozygotic stone-forming twins might help to define the interplay between environmental and genetic factors, and allow the identification of susceptibility genes involved in stone generation.
Comprehensive Kidney Stone Center, Division of Urologic Surgery, Duke University Medical Center, Durham, NC 27710, USA.
George E
GE
Haleblian
David A
DA
Cantor
Roger L
RL
Sur
Dean G
DG
Assimos
Glenn M
GM
Preminger
D000328:Adult; D000368:Aged; D002129:Calcium Oxalate / Q000652:urine; D015331:Cohort Studies; D003545:Cysteine / Q000652:urine; D004200:Diseases in Twins / Q000209:etiology* / Q000235:genetics; D005260:Female; D020022:Genetic Predisposition to Disease / Q000235:genetics; D006801:Humans; D008297:Male; D008659:Metabolic Diseases / Q000150:complications* / Q000235:genetics; D008875:Middle Aged; D053040:Nephrolithiasis / Q000209:etiology* / Q000235:genetics; D012189:Retrospective Studies; D014430:Twins, Monozygotic
D002129:Calcium Oxalate; D003545:Cysteine