Schimke immuno-osseous dysplasia (SIOD) is an autosomal recessive disorder caused by loss-of-function mutations in SWI/SNF related, matrix associated, actin dependent regulator of chromatin, subfamily a-like 1 (SMARCAL1), with clinical features of growth retardation, spondylo-epiphyseal dysplasia, nephrotic syndrome, and immunodeficiency. We report a patient with SIOD and SMARCAL1 splice mutation (IVS4-2 AϾG) in a nonconsanguineous Ashkenazi family, who came to our attention at 1 mo of age due to renal malformation and only later developed signs compatible with Schimke. Interestingly, residual SMARCAL1 mRNA levels in the patient's peripheral blood were lower compared with those observed in both asymptomatic brothers' carrying the same bi-allelic mutation, whereas the latter had levels similar to those found in heterozygous carriers (parents and sister). Examination of the carrier frequency of the splice mutation in the Ashkenazi population demonstrated 1 carrier in 760 DNA samples. In situ localization of SMARCAL1 in human kidneys as well as analysis of its temporal expression during murine nephrogenesis and in the metanephric organ culture suggested a role in the early renal progenitor population and after renal maturation. Thus, disease severity within the same family might be modified by the splicing machinery. The renal expression pattern of SMARCAL1 explains a broader spectrum of renal disease in SIOD than previously described. (Pediatr Res 63: 398-403, 2008) S chimke immuno-osseous dysplasia (SIOD) is characterized by autosomal recessive inheritance, spondyloepiphyseal dysplasia causing growth retardation, defective cellular immunity, progressive nephropathy leading to renal failure, hyperpigmented macules, and dysmorphic facial features (1-4). Half of SIOD patients also have hypothyroidism, half episodic cerebral ischemia, and a tenth bone marrow failure.SIOD is caused by mutations in SWI/SNF2 related, matrix associated, actin dependent regulator of chromatin, subfamily a-like 1(SMARCAL1) (5). SNF2 related proteins participate in the DNA nucleosome restructuring which commonly occurs during gene regulation and DNA replication, recombination, methylation, and repair (6,7).Recent analysis of detailed autopsies to correlate clinical and pathologic findings in SIOD identified T cell deficiency in peripheral lymphoid organs, defective chondrogenesis, focal segmental glomerulosclerosis (FSGS), cerebral ischemic lesions, and premature atherosclerosis (8).Herein, we report on a male patient, 6 y old, who came to our attention after birth due to renal malformation and later on developed growth retardation, bone dysplasia, and steroidresistant nephrotic syndrome and was shown to harbor a bi-allelic SMARCAL1 splice mutation. Investigation of his nonconsanguineous Ashkenazi family lead us to discover phenotypic diversity and variable expressivity of SMARCAL1 in the family along with low carrier frequency of the splice mutation in the Ashkenazi population. In addition, in situ localization of SMARCAL1 in the...