Clinical and Mutation Spectra of Cockayne Syndrome in India.

BACKGROUND: Cockayne syndrome is an autosomal recessive disorder caused by biallelic mutations in ERCC6 or ERCC8 genes. AIMS: To study the clinical and mutation spectrum of Cockayne syndrome. SETTING AND DESIGN: Medical Genetics Outpatient Department of Sanjay Gandhi Post Graduate Institute of Medical Sciences, Lucknow. This was a prospective study from 2007 to 2015. MATERIALS AND METHODS: Clinical details were recorded, and sequencing of ERCC6 and ERCC8 were performed. RESULTS AND CONCLUSIONS: Of the six families, one family had a homozygous mutation in ERCC8 and the other five families had homozygous mutations in ERCC6. Novel variants in ERCC6 were identified in four families. Phenotypic features may vary from severe to mild, and a strong clinical suspicion is needed for diagnosis during infancy or early childhood. Hence, molecular diagnosis is needed for confirmation of diagnosis in a child with a suspicion of Cockayne syndrome. Prenatal diagnosis can be provided only if molecular diagnosis is established in the proband.

Phenotypic diversity and genetic complexity of PAX3-related Waardenburg syndrome.

Waardenburg syndrome subtypes 1 and 3 are caused by pathogenic variants in PAX3. We investigated 12 individuals from four unrelated families clinically diagnosed with Waardenburg syndrome type 1/3. Novel pathogenic variants identified in PAX3 included single nucleotide variants (c.166C>T, c.829C>T), a 2-base pair deletion (c.366_367delAA) and a multi-exonic deletion. Two novel variants, c.166C>T and c.829C>T and a previously reported variant, c.256A>T in PAX3 were evaluated for their nuclear localization and ability to activate MITF promoter. The coexistence of two subtypes of Waardenburg syndrome with pathogenic variants in PAX3 and EDNRB was seen in one of the affected individuals. Multiple genetic diagnoses of Waardenburg syndrome type 3 and autosomal recessive deafness 1A was identified in an individual. We also review the phenotypic and genomic spectrum of individuals with PAX3-related Waardenburg syndrome reported in the literature.

Burn-McKeown syndrome with biallelic promoter type 2 deletion in TXNL4A in two siblings.

Burn-McKeown syndrome (BMKS) (MIM# 608572) is a rare condition caused by biallelic variants in TXNL4A. BMKS is characterized by craniofacial dysmorphism, choanal atresia, and normal intellect in affected individuals. BMKS has overlapping clinical features with Treacher Collins syndrome. Till date, 15 families have been described with BMKS. Homozygosity or compound heterozygosity of promoter deletions and null variants in TXNL4A are known to cause most cases of BMKS. We describe the first Indian family with two siblings with BMKS and promoter type 2 deletion in homozygous state.

Bain type of X-linked syndromic mental retardation in a male with a pathogenic variant in HNRNPH2.

Heterogeneous nuclear ribonucleoproteins (hnRNPs) are RNA binding proteins, which aid in maturation, stabilization, and transport of mRNA. They have a significant role in cellular nucleic acid metabolism. The hnRNPs alter gene expression and are linked to various neurodegenerative disorders and cancers. Previously, six unrelated girls with developmental delay, intellectual disability, and hypotonia were found to have de novo heterozygous pathogenic missense variants in HNRNPH2, located on the X chromosome. A gain-of-function effect was proposed for the variant and it was thought to be lethal in males as no surviving males were identified. We describe a family with two affected siblings, one male and one female, with a known pathogenic variant in HNRNPH2, possibly due to maternal germline mosaicism.

An emerging ribosomopathy affecting the skeleton due to biallelic variations in NEPRO.

Cartilage hair hypoplasia (CHH), anauxetic dysplasia 1, and anauxetic dysplasia 2 are rare metaphyseal dysplasias caused by biallelic pathogenic variants in RMRP and POP1, which encode the components of RNAse-MRP endoribonuclease complex (RMRP) in ribosomal biogenesis pathway. Nucleolus and neural progenitor protein (NEPRO), encoded by NEPRO (C3orf17), is known to interact with multiple protein subunits of RMRP. We ascertained a 6-year-old girl with skeletal dysplasia and some features of CHH. RMRP and POP1 did not harbor any causative variant in the proband. Parents-child trio exomes revealed a candidate biallelic variant, c.435G>C, p.(Leu145Phe) in NEPRO. Two families with four affected individuals with skeletal dysplasia and a homozygous missense variant, c.280C>T, p.(Arg94Cys) in NEPRO, were identified from literature and their published phenotype was compared in detail to the phenotype of the child we described. All the five affected individuals have severe short stature, brachydactyly, skin laxity, joint hypermobility, and joint dislocations. They also have short metacarpals, broad middle phalanges, and metaphyseal irregularities. Protein modeling and stability prediction showed that the mutant protein has decreased stability. Both the reported variants are in the same domain of the protein. Our report delineates the clinical and radiological characteristics of an emerging ribosomopathy caused by biallelic variants in NEPRO.

Locus and allelic heterogeneity and phenotypic variability in Waardenburg syndrome.

Waardenburg syndrome (WS) is a disorder of neural crest cell migration characterized by auditory and pigmentary abnormalities. We investigated a cohort of 14 families (16 subjects) either by targeted sequencing or whole-exome sequencing. Thirteen of these families were clinically diagnosed with WS and one family with isolated non-syndromic hearing loss (NSHL). Intra-familial phenotypic variability and non-penetrance were observed in families diagnosed with WS1, WS2 and WS4 with pathogenic variants in PAX3, MITF and EDNRB, respectively. We observed gonosomal mosaicism for a variant in PAX3 in an asymptomatic father of two affected siblings. For the first time, we report a biallelic pathogenic variant in MITF in a subject with WS2 and a biallelic variant in EDNRB was noted in a subject with WS2. An individual with isolated NSHL carried a pathogenic variant in MITF. Blended phenotype of NSHL and albinism was observed in a subject clinically diagnosed to have WS2. A phenocopy of WS1 was observed in a subject with a reported pathogenic variant in GJB2, known to cause isolated NSHL. These novel and infrequently reported observations exemplify the allelic and genetic heterogeneity and show phenotypic diversity of WS.

Familial choreoathetosis due to novel heterozygous mutation in PDE10A.

PDE10A encodes a dual cAMP-cGMP phosphodiesterase that is enriched in the medium spiny neurons of the corpus striatum in the brain and plays an important role in basal ganglia circuitry. Three unrelated patients with childhood onset chorea and striatal abnormalities on MRI brain with heterozygous de novo variants in PDE10A have been described previously. Two families with eight affected individuals with biallelic mutations in PDE10A have also been described previously. We report a family with multiple affected individuals with childhood onset chorea, striatal abnormalities, and a novel heterozygous mutation, c.1001T>G(p.F334C) in PDE10A which was identified by exome sequencing.

A novel variant in MED12 gene: Further delineation of phenotype.

MED12 is a multiprotein mediator complex, which has a role in cell growth and differentiation and has been implicated in three distinct X-linked intellectual disability syndromes with distinctive clinical features. These include Opitz-Kaveggia syndrome (FG syndrome), Lujan syndrome, and X-linked Ohdo syndrome. Recently MED12 variants have been implicated in isolated X-linked intellectual disability. We describe a 5-year-old male patient with intellectual disability and facial dysmorphism and a novel variant in MED12 gene identified by Whole Exome Sequencing. His dysmorphic facial features are distinct from the previously described phenotypes. With a strong genotype-phenotype correlation that is already known for MED12, this could be a new phenotype linked to MED12, thus expanding the phenotypic spectrum of MED12-related disorders.