A familial case of nail patella syndrome with a heterozygous in-frame indel mutation in the LIM domain of LMX1B

Identification of a novel LMX1B nonsense variant associated with congenital talipes equinovarus by prenatal exome sequencing: A case report

BACKGROUND

Congenital talipes equinovarus (CTEV) is a rotational foot deformity that affects muscles, bones, connective tissue, and vascular or neurological tissues. The etiology of CTEV is complex and unclear, involving genetic and environmental factors. Nail-patella syndrome is an autosomal dominant disorder caused by variants of the LIM homeobox transcription factor 1 beta gene (LMX1B, OMIM:602575). LMX1B plays a key role in the development of dorsal limb structures, the kidneys, and the eyes, and variants in this gene may manifest as hypoplastic or absent patella, dystrophic nails, and elbow and iliac horn dysplasia; glomerulopathy; and adult-onset glaucoma, respectively. This study aimed to identify pathogenic variants in a fetus with isolated talipes equinovarus diagnosed by ultrasound in the second trimester, whose father exhibited dysplastic nails and congenital absence of bilateral patella.

METHODS

Prenatal whole-exome sequencing (WES) of the fetus and parents was performed to identify the genetic variant responsible for the fetal ultrasound abnormality, followed by validation using Sanger sequencing.

RESULTS

A novel heterozygous nonsense variant in exon 6 of LMX1B (c.844C>T, p.Gln282*) was identified in the fetus and the affected father but was not detected in any unaffected family members. This nonsense variant resulted in a premature termination codon at position 282, which may be responsible for the clinical phenotype through the loss of function of the gene product.

CONCLUSIONS

Our study indicating that a fetus carrying a novel nonsense variant of LMX1B (c.844C>T, p.Gln282*) can exhibit isolated talipes equinovarus, which expands the LMX1B genotypic spectrum and is advantageous for genetic counseling.

A novel small deletion of LMX1B in a large Chinese family with nail-patella syndrome

BACKGROUND

Nail-patella syndrome (NPS) is an autosomal dominant developmental disorder most commonly characterized by dyplasia of nail or patella, the radial head or the humeral head hypoplasia, and, frequently ocular abnormalities and renal disease. It is caused by heterozygous loss-of-function mutations in the LMX1B gene, which encodes LIM homeodomain transcription factor and is essential for regulating the dorsal limb fate.

METHODS

A five generation pedigree was recruited. Genomic DNA was extracted from the peripheral blood samples. Mutation detection was performed by Sanger sequencing the LMX1B gene. In silico functional annotation of the variant was performed using the in silico predictors SIFT, PolyPhen-2 and Mutation Taster.

RESULTS

A novel heterozygous small deletion within exon 4 of LMX1B, c.712_714delTTC, was identified in a rare five-generation NPS pedigree. The mutation resulted in a deletion of the conserved amino acid phenylalanine at codon 238 (p.Phe238del), which located in the homeodomain of LMX1B may abolish DNA binding with the molecule. Conformational prediction showed that the variation could transform the helical structure comprising p.Phe234, p.Lys235, p.Ala236, and p.Ser237.

CONCLUSION

We identified a novel NPS-causing LMX1B mutation and expanded the spectrum of mutations in the LMX1B gene. The c.712_714delTTC mutation may affect the quaternary structure of LMX1B, which is essential for the specification of dorsal limb fate at both zeugopodal and autopodal levels, leading to typical NPS.

Novel missense mutation affecting the LIM-A domain of LMX1B in a family with Nail-Patella syndrome

Nail-patella syndrome (NPS) is a rare autosomal dominant disease characterized by developmental defects of dorsal limb structures, the kidney, and the eye, that manifest as dysplastic nails, hypoplastic or absent patella, elbow dysplasia, iliac horns, glomerulopathy, and adult-onset glaucoma, respectively. This disorder is inherited in an autosomal dominant mode and is caused by heterozygous loss-of-function mutations in the LMX1B gene, which encodes the LIM homeodomain transcription factor LMX1B. In this study, we report the clinical findings of a Spanish family, from the Canary Islands, with three affected members who displayed varying phenotypes. DNA sequence analysis identified a novel heterozygous missense mutation in LMX1B, c.305A>G, p.(Y102C), that segregated with the disease. The tyrosine residue affected by the mutation is highly conserved in evolution, and is located in the LIM-A domain, next to one of the cysteine residues involved in zinc binding, suggesting that p.(Y102C) affects LMX1B function by disturbing its interactions with other proteins. Our results expand the mutation spectrum of LMX1B and provide insight into the molecular mechanisms of NPS pathology.