Gene-Targeted Next Generation Sequencing Identifies PNPLA1 Mutations in Patients with a Phenotypic Spectrum of Autosomal Recessive Congenital Ichthyosis: The Impact of Consanguinity

Abstract

Autosomal recessive congenital ichthyosis is a heterogeneous group of disorders associated with mutations in at least nine distinct genes. To ascertain the molecular basis of ichthyosis patients in Iran, a country of approximately 80 million people with a high prevalence of customary consanguineous marriages, we have developed a gene-targeted next generation sequencing array consisting of 38 genes reported in association with ichthyosis phenotypes. In a subset of nine extended consanguineous families, we found homozygous missense mutations in the PNPLA1 gene, six of them being distinct and, to our knowledge, previously unpublished. This gene encodes an enzyme with lipid hydrolase activity, important for development and maintenance of the barrier function of the epidermis. These six mutations, as well as four previously published mutations, reside exclusively within the patatin-like subdomain of PNPLA1 containing the catalytic site. The mutations clustered around the active center of the enzyme or resided at the surface of the protein possibly involved in the protein-protein interactions. Clinical features of the patients showed considerable intra- and interfamilial heterogeneity. Knowledge of the specific mutations allows identification of heterozygous carriers, assisting in genetic counseling, prenatal testing, and preimplantation genetic diagnosis in extended families at risk of recurrence of this disorder, the incidence of which is significantly increased in consanguineous marriages.

Sixteen novel mutations in PNPLA1 in patients with autosomal recessive congenital ichthyosis reveal the importance of an extended patatin domain in PNPLA1 that is essential for proper human skin barrier function

“…and Lee et al . We identified in patient P1 the same homozygous mutation p.Ser19Leu found in two unrelated families by Vahidnezhad et al . Patients P4 and P11 show a splice‐site mutation (c.775 + 3A>T), while patients P6 and P7 share the missense mutation c.418T>C; p.Ser140Pro.…”

“…Mutations in nine genes are currently associated with ARCIs: ABCA12 , ALOX12B , ALOXE3 , CERS3 , CYP4F22 , NIPAL4 , TGM1 , PNPLA1 and SDR9C7 . Causative mutations in PNPLA1 have been described previously by our group in humans and dogs, and the results have been confirmed by others …”

“…All 10 previously described pathogenic PNPLA1 mutations are located within the patatin core domain (grey bars in Fig. ) . Likewise, 13 of our novel mutations are also located within this domain (amino acids 16–185; Figs ).…”

“…At amino acid position 34, Vahidnezhad et al . also report the mutation Ala34Pro . Patients P2, P11 and P16 share the deletion c.275delC; p.Pro92Argfs*8, while patients P1 and P16 share the mutation c.301A>G; p.Arg101Gly.…”

“…One mutation affects the serine residue at position 53 in the serine lipase motif (GTSAG) and the other one, aspartate residue 172 (DGG motif active site). Ser53 and Asp172 are parts of the catalytic dyad . Some of the pathogenic mutations seem to be more frequent, as they appear in more than one patient with ARCI.…”