Molecular analysis of LPIN1 in Jordanian patients with rhabdomyolysis

Abstract

Recessive mutations in LPIN1, which encodes a phosphatidate phosphatase enzyme, are a frequent cause of severe rhabdomyolysis in childhood. Hence, we sequenced the 19 coding exons of the gene in eight patients with recurrent hereditary myoglobinuria from four unrelated families in Jordan. The long-term goal is to facilitate molecular genetic diagnosis without the need for invasive procedures such as muscle biopsies. Three different mutations were detected, including the novel missense mutation c.2395G>C (Gly799Arg), which was found in two families. The two other mutations, c.2174G>A (Arg725His) and c.1162C>T (Arg388X), have been previously identified, and were found to cosegregate with the disease phenotype in the other two families. Intriguingly, patients homozygous for Arg725His were also homozygous for the c.1828C>T (Pro610Ser) polymorphism, and were exercise-intolerant between myoglobinuria episodes. Notably, patients homozygous for Arg388X were also homozygous for the c.2250G>C silent variant (Gly750Gly). Taken together, the data provide family-based evidence linking hereditary myoglobinuria to pathogenic variations in the C-terminal lipin domain of the enzyme. This finding highlights the functional significance of this domain in the absence of structural information. This is the first analysis of LPIN1 in myoglobinuria patients of Jordanian origin, and the fourth such analysis worldwide.

Keywords: C-LIP domain; Lipin-1; myoglobinuria.

Fig. 1

Sequencing chromatograms encompassing LPIN1 mutations, and phasing haplotypes. (A) c.2174G>A (Arg725His) in exon 17, heterozygous. The mutation cosegregated with the disease in family A, along with c.1828T (Pro610Ser). Unaffected siblings were wild type at both positions. (B) Phasing haplotypes constructed using the variants c.192+17C>T, c.193-47C>T, c.552C>T (p.Ile184Ile), and c.1828C>T (p.Pro610Ser), which were found in family A. (C) c.2395G>C (Gly799Arg) in exon 18, heterozygous. (D) c.1162C>T (Arg388X) in exon 8, heterozygous. Arrows mark nucleotide substitutions.

Fig. 2

Multiple sequence alignment of lipin proteins from various species. Arg725 and Gly799 in the C-LIP domain, which were found mutated in different families, are highlighted in green. Asp678, Asp680, Ser723, and Asp804, which are strictly conserved in haloacid dehalogenase-like proteins including lipins, were used to anchor alignments, and are highlighted in red. Alignments were generated in CLUSTAL Omega.