Novel mutations c.28G>T (p.Ala10Ser) and c.189G>T (p.Glu63Asp) in WDR62 associated with early onset acanthosis and hyperkeratosis in a patient with autosomal recessive microcephaly type 2

Abstract

Microcephaly (MCPH) is a developmental disorder characterized by reduced brain size and intellectual disability. A proportion of microcephaly is caused by defects in a single gene. Microcephaly 2 (MCPH2) is one of the most frequent subtypes of MCPH.WD repeat-containing protein 62 gene (WDR62) is the most frequently mutated gene in MCPH2 patients. Phenotypes involving dermatological changes in MCPH2 have not been reported. We have identified and investigated a 5-year-old Chinese girl with markedly reduced brain size (86% of normal size), intellectual disability and psychomotor developmental delay. The patient also exhibited spattered blisters and reduced hair density on her head, anisochromasia with reticular hyperpigmentation and hypopigmentation on the trunk, which she has had since the age of 4 and had been found by her parents. Histological examination of a skin biopsy revealed acanthosis, hyperkeratosis and necrotic keratinocytes. Whole exome and Sanger sequencing identified two novel missense mutations, c.28G>T and c.189G>T, in the WDR62 gene. Both the mutations non-synonymously affect evolutionarily conserved amino acids and are predicted to be disease causing. We report the first case of MCPH2 that also presented with marked dermatological changes. Our findings expand the mutational and phenotypical spectra of MCPH2 and are valuable in the mutation-based pre- and post-natal screening and genetic diagnosis for MCPH2.

Keywords: Pathology Section; WDR62 mutation; compound heterozygosity; exome sequencing; microcephaly 2; novel mutations.

Figure 1

A. Pedigree of the family. The filled symbol indicates the patient (proband), and the half-filled symbols show the carrier parents, who were heterozygous carriers but were unaffected. The arrow points to the proband. B. Facial phenotype of the patient, which shows the sloping forehead, the convex facial profile, the full lips, and the small chin. The appearance of low-set and posteriorly rotated ears in the lateral picture is partly due to reclamation of the head. It also shows the reduced hair on the top of the head.

Figure 2. Brain images

A. and B. showing the expansion of bilateral brain ventricles, dysplasia of the brain white matter and suspicious schizencephaly in the right parietal lobe, C. dysplasia of the temporal lobe with small hippocampus and enlarge temporal horn, D. obvious expansion of the fourth ventricle and slight atrophy of cerebellum, and E. slight atrophy of the brain stem and thinning of the corpus callosum with absence of the splenium.

Figure 3

A. and B. Pictures show spattered pigmentation on the trunk. C. Three blisters on the skin. D. HE slides of the skin biopsy showing hyperkeratosis in the skin and porokeratosis. Stratum spinosum thickened slightly with edema in intracellular and intercellular areas. Pigment granules in the basal layer with increased punctate liquefaction degeneration. Few lymphocytes infiltrate beside blood vessel in the shallow corium layer.

Figure 4. Partial DNA sequences in the WDR62 by Sanger sequencing of the family

Upper line: the proband, middle line: the father, bottom line: the mother. Arrows point to the mutations. The proband inherited both c.28G>T and c.189G>T mutations. The father carries the c.28G>T mutation, and the mother carries the c.189G>T mutation.

Figure 5. Amino acid alignment of the wild-type protein encoded by WDR62

(Homo sapiens) (GenBank Accession: NM_001083961.1) with mouse (Mus musculus) (GenBank Accession: NM_146186.3), rhesus monkey (Macaca mulatta) (GenBank Accession: AFH29290.1), chimpanzee (Pan troglodytes) (GenBank Accession: JAA38944.1), zebrafish (Danio rerio) (GenBank Accession: CM002899.1), cattle (Bos taurus) (GenBank Accession: GK000018.2), dog (Canis lupus familiaris) (GenBank Accession:CM000001.3), and pig (Sus scrofa) (GenBank Accession: CM000817.4). The two boxes show that amino acids 10 and 63 are conserved across these species.

Figure 6. Filtering process for pathogenic mutations in all variations obtained by exome sequencing

*Databases used: dbSNP, Hapmap, 1000 Genomes Project and BGI's in-house database of ~30000 Chinese people. SNV: single nucleotide variation. Indel: small insertion and deletion.