Mutation of FLNA attenuating the migration of abdominal muscles contributed to Melnick-Needles syndrome (MNS) in a family with recurrent miscarriage

BACKGROUND

Filamin A, encoded by the X-linked gene FLNA, links the cell membrane with the cytoskeleton and acts as a regulator of the actin cytoskeleton. Mutations in FLNA cause a large spectrum of congenital malformations during embryonic development, including Melnick-Needles syndrome (MNS). However, reports of MNS, especially in males, are rare, and the pathogenesis molecular mechanisms are not well understood.

METHODS

We found a family with two consecutive miscarriages of similar fetuses with multiple malformations. DNA was extracted from peripheral blood and tissues, and whole exome sequencing was performed for genetic analysis. Then, we created a C57BL/6 mouse with a point mutation by CRISPR/Cas-mediated genome engineering. The migration of primary abdominal muscle cell was detected by wound healing assay.

RESULTS

The first fetus showed congenital hygroma colli and omphalocele identified by ultrasound at 12 wks; the second fetus showed hygroma colli and thoraco abdominoschisis at 12 wks, with a new hemizygous mutation c.4420G>A in exon 26 of the FLNA gene, which is predicted to cause an amino acid substitution (p.Asp1474Asn). The mother and grandmother were both present in the c.4420G>A heterozygous state, and the mother's healthy brother had wild-type FLNA. These FLNA-mutated mice exhibited a broader central gap between the rectus abdominis than the wild type (WT), similar to the midline structure dysplasia of the abdominal wall in the two fetuses. Wound healing assays showed the attenuated migration capacity of abdominal muscle cells in mice with mutated FLNA. Finally, we summarized the cases of MNS with FLNA mutation from the accessible published literature thus far.

CONCLUSION

Our research revealed a mutation site of the FLNA for MNS and explored the mechanism of midline structure dysplasia in the abdominal wall of male patients, which could provide more evidence for the clinical diagnosis and genetic counseling of families with these disorders.

A family of Melnick-Needles syndrome: a case report

BACKGROUND

Melnick-Needles syndrome (MNS) is an extremely rare osteochondrodysplasia caused by a mutation of FLNA, the gene encoding filamin A. MNS is inherited in an X-linked dominant manner. In this study, we describe three members of the same family with MNS, who exhibited different phenotypic severity despite having an identical FLNA gene mutation.

CASE PRESENTATION

The patient was 16 months old, with a history of delayed physical development, multiple upper respiratory infections and otitis media episodes. She was referred to our orthopedic clinic because of bowed legs and an abnormal plain chest radiograph. Both upper and lower extremities were bowed. Plain X-rays showed thoracolumbar kyphoscoliosis, with anterior and posterior vertebral scalloping, and thin, wavy ribs. Hypoplasia of the pubis and ischium, with bilateral coxa valga, were also noted. Target exome sequencing revealed a heterozygous mutation of FLNA, c.3578 T > C, p.Lys1193Pro, which confirmed the diagnosis of MNS. Her older sister and mother had minimal deformities of the axial and extremity skeleton, but genetic analyses revealed the same FLNA mutation as the patient. The mutation identified in this family has not been previously reported.

CONCLUSION

This report illustrates the potential inherited nature of MNS and the phenotypic variability of clinicoradiologic characteristics. In patients with traits suggestive of MNS, a careful medical and family history should be obtained, and genetic testing should be performed for the patient, as well as all family members.

A recurrent mutation causing Melnick-Needles syndrome in females confers a severe, lethal phenotype in males

Melnick-Needles syndrome (MNS; MIM 309350) is an X-linked skeletal dysplasia caused by mutations in FLNA. Females with the condition present with characteristic facial features, short stature, skeletal anomalies, including poorly modeled and sclerotic bones, and structural abnormalities such as cardiac and urological defects. Previously males were thought to present with either a mild phenotype compatible with life or a severe lethal presentation depending on the maternal phenotype. The discovery of a limited number of mutations in FLNA as the cause of the condition has clarified the molecular basis of the disorder, but only a very small number of severely affected males have been reported with MNS. Furthermore, no mildly affected males have been described with a molecular confirmation of the condition. In this report, we describe the clinical and molecular findings of a mildly affected mother with MNS and her severely affected son. They shared a well-documented disease-causing variant in FLNA, p.(Ala1188Thr), one of two highly recurrent mutations leading to the disorder. This is only the fourth report of a male with perinatal lethal MNS and a molecular confirmation; it is the first description of this specific mutation in a male.