Hemoglobin (Hb) Bassett, an abnormal Hb variant with a markedly reduced oxygen affinity, was discovered in a Caucasian (Anglo-Saxon) male child who experienced episodes of cyanosis. Cation-exchange and reversed-phase (RP) high-performance liquid chromatography (HPLC) showed that the patient has an abnormal Hb, with a mutation in the a-globin. Tryptic peptide digest of the abnormal a-globin with subsequent HPLC analysis revealed abnormal elution of the a-T11 peptide. Further studies with Edman sequencing and electrospray mass spectrometry of tryptic peptide a-T11, as well as structural analysis by X-ray crystallography revealed an AspfiAla substitution at the a94 (G1) position, a match for Hb Bassett. Detailed functional studies showed that this Hb variant had a markedly reduced oxygen affinity (P 50 at pH 7.0 = 22 mmHg; Hb A P 50 = 10.5 mmHg), reduced Bohr effect (-0.26 compared to -0.54 in Hb A), and low subunit cooperativity (n = 1.4, compared to 2.6 in Hb A). X-ray crystallography results explain the probable effects of the structural modification on the oxygen-binding properties of this Hb variant. Am.
Myelin basic protein (MBP) contributes to peripheral and central nervous system myelin. Developmental myelinopathies exist on a clinical spectrum, but MBP is not included on leukodystrophy or CMT gene panels. This ring chromosome 18 case presents serial MRI and EMG/NCS, shedding light on the early clinical course of the disorder.
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