Variant non ketotic hyperglycinemia is caused by mutations in LIAS, BOLA3 and the novel gene GLRX5.

Patients with nonketotic hyperglycinemia and deficient glycine cleavage enzyme activity, but without mutations in AMT, GLDC or GCSH, the genes encoding its constituent proteins, constitute a clinical group which we call 'variant nonketotic hyperglycinemia'. We hypothesize that in some patients the aetiology involves genetic mutations that result in a deficiency of the cofactor lipoate, and sequenced genes involved in lipoate synthesis and iron-sulphur cluster biogenesis. Of 11 individuals identified with variant nonketotic hyperglycinemia, we were able to determine the genetic aetiology in eight patients and delineate the clinical and biochemical phenotypes. Mutations were identified in the genes for lipoate synthase (LIAS), BolA type 3 (BOLA3), and a novel gene glutaredoxin 5 (GLRX5). Patients with GLRX5-associated variant nonketotic hyperglycinemia had normal development with childhood-onset spastic paraplegia, spinal lesion, and optic atrophy. Clinical features of BOLA3-associated variant nonketotic hyperglycinemia include severe neurodegeneration after a period of normal development. Additional features include leukodystrophy, cardiomyopathy and optic atrophy. Patients with lipoate synthase-deficient variant nonketotic hyperglycinemia varied in severity from mild static encephalopathy to Leigh disease and cortical involvement. All patients had high serum and borderline elevated cerebrospinal fluid glycine and cerebrospinal fluid:plasma glycine ratio, and deficient glycine cleavage enzyme activity. They had low pyruvate dehydrogenase enzyme activity but most did not have lactic acidosis. Patients were deficient in lipoylation of mitochondrial proteins. There were minimal and inconsistent changes in cellular iron handling, and respiratory chain activity was unaffected. Identified mutations were phylogenetically conserved, and transfection with native genes corrected the biochemical deficiency proving pathogenicity. Treatments of cells with lipoate and with mitochondrially-targeted lipoate were unsuccessful at correcting the deficiency. The recognition of variant nonketotic hyperglycinemia is important for physicians evaluating patients with abnormalities in glycine as this will affect the genetic causation and genetic counselling, and provide prognostic information on the expected phenotypic course.

Ornithine transcarbamylase deficiency and pregnancy: A case series and review of recommendations.

Background: Ornithine transcarbamylase deficiency (OTCD) is a rare disorder of the urea cycle that obstetricians should be aware of in order to guide management for pregnant carriers of the X-linked gene that causes the condition. Cases: We present the pregnancy management and outcomes of two women with OTCD. The particular manifestations of the disease drive antenatal, intrapartum and postpartum management. Conclusion: Preconception counseling, early prenatal diagnostics and multidisciplinary intrapartum and postpartum management plans contribute to improved outcomes for patients.

Biotinidase deficiency: novel mutations and their biochemical and clinical correlates.

Biotinidase deficiency is a defect in the recycling of the vitamin biotin. Biotin supplementation can markedly improve the neurological and cutaneous symptoms of affected children and prevent symptoms in children identified by newborn screening or treated since birth. We have determined thirteen novel mutations in children with the disorder. Two nonsense mutations, eight single missense mutations, three allelic double missense mutations, and two are polymorphisms were identified in the biotinidase gene (BTD). One of the missense mutations, c.734G>A (p. C245Y), is the first to be reported that alters the cysteine in the putative location crucial for ester formation and binding of the biotinyl-moiety in the active site of the enzyme. These mutations add to the growing list of mutations that are helping to delineate structure/function relationships of the enzyme.

A new case of Okamoto syndrome.

We report a 6 month old boy with congenital hydronephrosis, cleft palate, severe hypotonia, congenital heart defect, developmental delay, and characteristic facial features with an open mouthed appearance and full lower lip, who we believe is the third reported case of Okamoto syndrome. Okamoto syndrome is a recently described distinctive multiple congenital anomaly syndrome encompassing the above features for which an etiologic factor has not yet been identified. Our patient also had idiopathic splenomegaly and non-specific MRI changes in the brain, not reported in the first two cases.

Mutations in the transmembrane natriuretic peptide receptor NPR-B impair skeletal growth and cause acromesomelic dysplasia, type Maroteaux.

The homodimeric transmembrane receptor natriuretic peptide receptor B (NPR-B [also known as guanylate cyclase B, GC-B, and GUC2B]; gene name NPR2) produces cytoplasmic cyclic GMP from GTP on binding its extracellular ligand, C-type natriuretic peptide (CNP). CNP has previously been implicated in the regulation of skeletal growth in transgenic and knockout mice. The autosomal recessive skeletal dysplasia known as "acromesomelic dysplasia, type Maroteaux" (AMDM) maps to an interval that contains NPR2. We sequenced DNA from 21 families affected by AMDM and found 4 nonsense mutations, 4 frameshift mutations, 2 splice-site mutations, and 11 missense mutations. Molecular modeling was used to examine the putative protein change brought about by each missense mutation. Three missense mutations were tested in a functional assay and were found to have markedly deficient guanylyl cyclase activity. We also found that obligate carriers of NPR2 mutations have heights that are below the mean for matched controls. We conclude that, although NPR-B is expressed in a number of tissues, its major role is in the regulation of skeletal growth.