Nonketotic hyperglycinemia (NKH) is an inborn error of metabolism characterized by accumulation of glycine in body fluids and various neurological symptoms. NKH is caused by deficiency of the glycine cleavage multi-enzyme system with three specific components encoded by GLDC, AMT, and GCSH. We undertook the first comprehensive screening for GLDC, AMT, and GCSH mutations in 69 families (56, six, and seven families with neonatal, infantile, and late-onset type NKH, respectively). GLDC or AMT mutations were identified in 75% of neonatal and 83% of infantile families, but not in late-onset type NKH. No GCSH mutation was identified in this study. GLDC mutations were identified in 36 families, and AMT mutations were detected in 11 families. In 16 of the 36 families with GLDC mutations, mutations were identified in only one allele despite sequencing of the entire coding regions. The GLDC gene consists of 25 exons. Seven of the 32 GLDC missense mutations were clustered in exon 19, which encodes the cofactor-binding site Lys754. A large deletion involving exon 1 of the GLDC gene was found in Caucasian, Oriental, and black families. Multiple origins of the exon 1 deletion were suggested by haplotype analysis with four GLDC polymorphisms. This study provides a comprehensive picture of the genetic background of NKH as it is known to date.

Purpose: Fabry disease, a genetic deficiency of ␣-galactosidase A, is characterized by pathogenic cellular accumulation of globotriaosylceramide. During clinical trials, recombinant human ␣-galactosidase A (agalsidase beta; Fabrazyme®, Genzyme Corporation, Cambridge, MA), infused intravenously at 1.0 mg/kg every 2 weeks for 6 months, cleared or reduced globotriaosylceramide in renal, cardiac, and dermal microvascular endothelia and other cells, with results sustained for up to 5 years in most patients evaluated. This study explored whether a lower dose could maintain globotriaosylceramide clearance achieved with 1.0 mg/kg. Methods: Cellular globotriaosylceramide levels were assessed histologically in kidney and skin biopsies from 21 adult Fabry males treated for 6 months at 1.0 mg/kg/2 weeks followed by 18 months at 0.3 mg/kg/2 weeks. Results: In kidney interstitial capillary endothelium, the primary endpoint, globotriaosylceramide clearance was achieved in 100% of patients with 1.0 mg/kg and maintained in 90% with 0.3 mg/kg. In seven other renal cell types and superficial dermal capillary endothelium, globotriaosylceramide reduction or clearance was maintained with 0.3 mg/kg in ϳ70% of patients. Conclusions: A lower dose of agalsidase beta may be sufficient in some, but not all, patients with Fabry disease to maintain the cellular globotriaosylceramide clearance achieved with 1.0 mg/kg/2 weeks. Long-term clinical effects of transitioning to the lower dose have not been evaluated. Genet Med 2009:11(4):256 -264.

TMEM70 deficiency is a panethnic, multisystemic disease with variable outcome depending mainly on adequate management of hyperammonaemic crises in the neonatal period and early childhood.

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