A KRT6A mutation p.Ile462Asn in a Chinese family with pachyonychia congenita, and identification of maternal mosaicism: a case report

Background Pachyonychia congenita (PC, OMIM #167200, #167210, #615726, #615728, and #615735) is a rare autosomal dominant disorder caused by keratin gene mutations in KRT6A,KRT6B,KRT6C,KRT16 or KRT17. It is characterized with nail dystrophy and palmoplantar keratoderma (PPK). The most prominent manifestation is plantar pain. This is a further unusual case of parental mosaicism in PC. Although very rare, germ cell mosaicism should be considered when providing genetic counselling for unaffected parents of a child with PC. Case presentation We report the case of a 5-year-old boy with thickening nails and oral leukokeratosis at birth. He began to develop palmoplantar keratoderma at 2 years old and his sister has similar clinical manifestation characterized with nail discoloration and thickening. A previously reported heterozygous mutation, p.Ile462Asn, was identified in KRT6A in the proband and his affected sister. SNaPshot sequencing revealed mosaicism at a level of 2.5% and 4.7% in DNA from blood and hair bulbs from the unaffected mother. HiSeq deep sequencing demonstrated low-grade mosaicism in the patient’s younger sister and parents. Conclusion These findings indicate the ability of WES and SNaPshot sequencing to detect low-frequency mosaic mutations. Although very rare, germinal mosaicism should be considered when genetic counseling is given to families with presumed spontaneous cases of PC.

Pachyonychia Congenita Type PC-K6a: The first report in the Vietnamese population

Background: Pachyonychia congenita (PC) comprises a group of rare autosomal dominant genetic disorders. It is characterized by hypertrophic nail dystrophy, focal palmoplantar keratoderma, follicular keratosis, and oral leukokeratosis. It is associated with mutations in five differentiationspecific keratin genes: KRT6A, KRT6B, KRT6C, KRT16, or KRT17. The case is being reported for its rarity. To the best of our knowledge, this is the first report of PC, from Vietnam, confirmed by genetic analysis. Case presentation: A four-year-old Vietnamese girl presented with a thickened nail and oral leukokeratosis soon after birth. She was diagnosed with onychomycosis and chronic oral candidiasis and was treated with systemic anti-fungals in children's hospitals and dermatology departments multiple times; however, no treatments were effective. In collaboration with the International Pachyonychia Congenita Research Registry (IPCRR), the clinical features were consistent with a diagnosis of PC type PC-K6a. The genetic testing, performed through the IPCRR, shows a K6a N171K mutation. Conclusions: The IPCRR helps screen PC's clinical features and confirm a diagnosis at the molecular level, which is beneficial and crucial for validating the condition's clinical impression.

A KRT6A Mutation p.Ile462Asn In A Chinese Family With Pachyonychia Congenita, And Identification of Maternal Mosaicism

Background: Pachyonychia congenita (PC, OMIM #167200, #167210, #615726, #615728, and #615735) is a rare autosomal dominant disorder caused by keratin gene mutations in KRT6A, KRT6B, KRT6C, KRT16 or KRT17. It is characterized with nail dystrophy and palmoplantar keratoderma (PPK). The most prominent manifestation is plantar pain. This is the first reported case of maternal mosaicism in PC. Although very rare, germ cell mosaicism should be considered when providing genetic counselling for unaffected parents of a child with PC. Methods: Genomic DNA was extracted from peripheral blood samples, hair bulbs, buccal smears and the father’s germ cells. The entire coding and flanking intronic sequences of 5 keratin genes were screened for mutations in every individuals of the family by Sanger sequencing. We used whole exome sequencing (WES) to search for mosaicism in the parents who had no KRT6A mutation identified by Sanger sequencing. Mosaicism was confirmed by SNaPshot sequencing and HiSeq deep sequencing.Results: A previously reported heterozygous mutation, p.Ile462Asn, was identified in KRT6A in the proband and his affected sister. The variant was detected in one sequencing read from 86 sequencing reads from DNA from the mother’s blood by WES. The mutation was not identified in DNA from the father’s blood. Frequency of reads was 47% and 49% in proband and his sister, respectively. SNaPshot sequencing revealed mosaicism at a level of 2.5% and 4.7% in DNA from blood and hair bulbs from the unaffected mother. HiSeq deep sequencing demonstrated low-grade mosaicism in the patient’s younger sister and parents.Conclusion: These findings indicate the ability of WES and SNaPshot sequencing to detect low-frequency mosaic mutations. Although very rare, germinal mosaicism should be considered when genetic counseling is given to families with presumed spontaneous cases of PC.

A Case Study of Pachyonychia Congenita in Bangladesh

In 1906 Jadassohn and Lewandowsky described a rare genodermatoses and named it pachyonychia congenita. Pachy means thick. It is a group of genodermatoses involving keratin mutation with thickened nails and variable associated findings. Pachyonychia congenita is a rare disease having four types. However, type 1 and type 2 can be considered common among them. It can often mimic with fungal infection as nail hyperkeratosis can occur in both.