The presenting clinical features in neutropenia associated with metabolic diseases (Table 9-6) are lethargy, vomiting, ketosis, and dehydration during the neonatal period, failure to thrive, and growth retardation. The marrow is hypoplastic in these conditions, with decreased numbers of myeloid precursors. Idiopathic hyperglycin-emia and methylmalonic acidemia also have associated thrombocytopenia.
In glycogen storage disease type IB, there is impairment of glucose-6-phosphate-translocase, an enzyme necessary for the transport of glucose-6-phosphate from the cytoplasm to the endoplasmic reticulum, the site where glucose-6-phosphate is hydrolyzed to glucose and inorganic phosphate by an enzyme glucose-6-phos-phatase. As a result of the low availability of glucose, these patients develop hypo-glycemia, defective chemotaxis, and recurrent infections. The mechanism of neutropenia is not known in this disease. The bone marrow is hypercellular with abundant neutrophils.
Barth syndrome is characterized by cardiomyopathy, neutropenia, skeletal myopa-thy, growth retardation, low creatinine levels, mitochondrial abnormalities, and organic aciduria. It is a sex-linked recessive disorder. It results from mutations in the gene G4.5, a member of a tafazzin family protein.
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