Burwinkel B, Moses S W, Kilimann M W
Institut für Physiologische Chemie, Ruhr-Universität Bochum, Germany.
Hum Genet. 1997 Dec;101(2):170-4. doi: 10.1007/s004390050608.
We have identified mutations in the phosphorylase kinase (Phk) beta subunit gene in a male patient with liver glycogenosis caused by Phk deficiency. The patient's DNA has been analyzed for mutations in the genes encoding the alpha L, beta, and gamma TL subunits of Phk, all of which can be responsible for liver glycogenosis, by a strategy primarily based on reverse transcription/polymerase chain reaction of blood RNA and complemented by analysis of genomic DNA. His alpha L and gamma TL coding sequences are normal, whereas he is compound-heterozygous for two mutations in the beta subunit gene, PHKB. The first is a splice-site mutation (IVS4 [-2A-->G]) causing the reading-frame-disrupting deletion of exon 5 in the mRNA from this allele. The second is an Ala117Pro missense mutation, also in exon 5. This is the first missense mutation identified in PHKB, as opposed to nine translation-terminating mutations described to date. It offers an explanation for the unique biochemical phenotype of this patient. In his leukocytes, low Phk activity is measured when tested with the endogenous liver isoform of phosphorylase as the protein substrate, but normal activity is observed when tested with muscle phosphorylase added in vitro. In contrast, Phk activity in his erythrocytes is low with both substrates. The missense mutation may selectively impair the interaction of Phk with one isoform of its substrate protein and may destabilize the enzyme in a cell-type-specific way. This phenotype shares some aspects with X-linked liver glycogenosis subtype 2 (XLG2), a variant of liver Phk deficiency arising from missense mutations in the alpha L subunit gene (PHKA2), but differs from XLG2 in other respects. The present case demonstrates that mutations in Phk genes other than PHKA2 can also be associated with untypically high activity in certain blood cell types. Moreover, it emphasizes that missense mutations in Phk may cause unusual patterns of tissue involvement that would not be predicted a priori from the tissue specificity of expression of the mutated gene sequences.
我们在一名因磷酸化酶激酶（Phk）缺乏导致肝糖原贮积症的男性患者中，鉴定出了磷酸化酶激酶β亚基基因的突变。通过一种主要基于血液RNA逆转录/聚合酶链反应并辅以基因组DNA分析的策略，对该患者的DNA进行了分析，以检测编码Phk的αL、β和γTL亚基的基因中的突变，所有这些亚基都可能导致肝糖原贮积症。他的αL和γTL编码序列正常，而他在β亚基基因PHKB中存在两个突变的复合杂合子。第一个是剪接位点突变（IVS4 [-2A→G]），导致该等位基因的mRNA中外显子5发生读码框破坏缺失。第二个是Ala117Pro错义突变，也在外显子5中。这是在PHKB中鉴定出的首个错义突变，与迄今描述的9个翻译终止突变不同。它为该患者独特的生化表型提供了解释。在他的白细胞中，以内源性肝脏磷酸化酶同工型作为蛋白质底物进行检测时，测得的Phk活性较低，但在体外添加肌肉磷酸化酶进行检测时，观察到活性正常。相比之下，他的红细胞中两种底物的Phk活性均较低。错义突变可能选择性地损害Phk与其底物蛋白的一种同工型的相互作用，并可能以细胞类型特异性的方式使酶不稳定。这种表型与X连锁肝糖原贮积症2型（XLG2）有一些共同之处，XLG2是肝Phk缺乏的一种变体，由αL亚基基因（PHKA2）中的错义突变引起，但在其他方面与XLG2不同。本病例表明，除PHKA2外，Phk基因的突变也可能与某些血细胞类型中异常高的活性相关。此外，它强调Phk中的错义突变可能导致组织受累的异常模式，而这些模式无法根据突变基因序列表达的组织特异性预先预测。
