A number sign (#) is used with this entry because of evidence that smooth muscle dysfunction syndrome (SMDYS) is caused by heterozygous mutation in the ACTA2 gene (102620) on chromosome 10q23.

See also familial thoracic aortic aneurysm (AAT6; 611788) and moyamoya disease-5 (MYMY5; 614042), which can also be caused by ACTA2 mutation.

Smooth muscle dysfunction syndrome (SMDYS) presents with a recognizable pattern of complications, including congenital mydriasis, patent ductus arteriosus (PDA), pulmonary artery hypertension, aortic and other arterial aneurysms, moyamoya-like cerebrovascular disease, intestinal hypoperistalsis and malrotation, and hypotonic bladder. It is caused by heterozygous mutations of the ACTA2 gene altering the arginine-179 codon (summary by Regalado et al., 2018).

Milewicz et al. (2010) described 7 unrelated patients, ranging in age from 11 to 27 years, who had clinical findings suggestive of vascular disease, consistent with previous ACTA2 mutations. However, there was higher penetrance and earlier onset of vascular disease and additional multisystem smooth muscle dysfunction was manifest. Three of these patients had previously been described by Khan et al. (2004), Lemire et al. (2004), and Ades et al. (1999), respectively. All patients shared the features of congenital mydriasis, or fixed dilated pupils, as well as patent ductus arteriosus requiring repair in infancy. The patient previously reported by Lemire et al. (2004) had aortic coarctation that was repaired at age 4 months. All patients subsequently developed fusiform ascending aortic aneurysms extending to the arch during childhood, and 5 of 7 required surgical repair at age 10 to 25 years. The patient previously reported by Ades et al. (1999) had a dissection at 14 years of age. In addition to the aortic disease, all patients had cerebral vascular abnormalities including fusiform dilatation of the intimal carotid artery from the cavernous to the clinoidal segments, and the terminal region of the internal carotid arteries showed mild to moderate tapering indicative of stenosis of the artery and consistent with changes observed in Moyamoya disease (see 252350). Two of the patients, one reported by Milewicz et al. (2010) and one reported by Khan et al. (2004), underwent neurosurgical bypass for revascularization for Moyamoya disease. All 5 patients for whom imaging was reported had bilateral periventricular white matter hyperintensities, and 1 had changes consistent with a middle and anterior cerebral artery stroke. One patient had colpocephaly with a thin corpus callosum and somewhat small cerebral vermis and was diagnosed with developmental delay. In addition to the vascular abnormality, additional evidence of smooth muscle dysfunction included congenital mydriasis, hypotonic bladder, malrotation, and hyperperistalsis of the gastrointestinal tract. Two patients had malrotation. One patient had gallstones that spontaneously resolved and subsequently presented with hydrops of the gallbladder without evidence of residual gallstones. Biopsies of the esophagus, stomach, and small intestine revealed normal ganglionic cells and no specific neural or smooth muscle pathology. Four of the 5 patients for whom data were available had tachypnea at birth. One patient had hyperinflation of the upper lung segment, a hypoplastic lower lung segment, and a dilated pulmonary trunk at 14 years of age. The patient previously reported by Lemire et al. (2004) had evidence of cystic lung disease as an infant with biopsies showing alveolar dysgenesis consistent with developmental defect. One patient was diagnosed with primary pulmonary hypertension and underwent bilateral lung transplantation at age 18 months. The lung pathology showed pulmonary arterial hypertensive changes with smooth muscle cell hyperplasia and neointimal fibrocellular proliferative lesions. In addition, 2 out of 3 males had unilateral undescended testes. Two of the patients had asthma, and several patients had microaneurysms. One patient had microaneurysms of the retina, and one had a right ophthalmic artery occlusion.

Yetman et al. (2015) described 3 unrelated patients with SMDYS, including 1 patient (patient E) previously reported by Milewicz et al. (2010). Age at presentation ranged from birth to 1 month, and all 3 presented with an aneurysmal patent ductus arteriosus. One patient died of a pulmonary hypertensive crisis at 11 months of age. All 3 patients had aortic dilation, which began at ages 2 months, 22 months, and 7 years, respectively, with relatively rapid progression during childhood. All 3 also had abnormalities of the aortic valve and aortic coarctation. Other findings in all 3 patients included congenital mydriasis, retinal vessel tortuosity, pulmonary hypertension, and cerebrovascular findings, including moyamoya disease in one, a beaded appearance of cerebrovascular vessels with aneurysmal dilation and narrowing in another, and diffuse aneurysmal dilation of the right internal carotid artery in the third. Findings present in 2 patients included umbilical varix, lung disease, malrotation with volvulus, and vesicoureteral reflux. Periventricular white matter abnormalities were seen on imaging in all 3 patients.

Moreno et al. (2016) reported a 2.75-year-old Brazilian girl (patient 7) in whom prenatal megacystis, hydroureter, and hydronephrosis were detected. After birth, she presented with congenital mydriasis, intestinal malrotation, and symptoms of intestinal hypoperistalsis including vomiting and constipation. Cardiovascular anomalies included atrial septal defect, ductus arteriosus aneurysm, and pulmonic valve dilation. Brain MRI/MRA showed increased signal suggestive of terminal ischemic injuries, as well as bilateral stenosis of the extracranial carotid artery with straightened arterial course, including the terminal segments, as well as a hypoplastic posterior circulation system with significant reduction of basilar flow. She received parenteral nutrition in the first months of life and was maintained on an enteral diet via gastrostomy tube.

Regalado et al. (2018) reviewed the medical records of 33 patients with SMDYS. Patients ranged in age from newborn to 37 years. Age of diagnosis ranged from newborn to 36 years. Most (21 of 33) patients were female. All patients had congenital mydriasis and related pupillary abnormalities at birth and presented in infancy with a patent ductus arteriosus or aortopulmonary window. Patients had cerebrovascular disease characterized by small vessel disease (hyperintense periventricular white matter lesions; 95%), intracranial artery stenosis (77%), ischemic strokes (27%), and seizures (18%). Twelve (36%) patients had thoracic aortic aneurysm repair or dissection at median age of 14 years, and aortic disease was fully penetrant by the age of 25 years. Three (9%) patients had axillary artery aneurysms complicated by thromboembolic episodes. Nine patients died between the ages of 0.5 and 32 years due to aortic, pulmonary, or stroke complications, or unknown causes. Pulmonary complications of this condition include pulmonary arterial hypertension, and 1 patient required lung transplant for this complication at the age of 18 months. Gut malrotation was observed in 30% of patients. Reproductive complications included atonic uterus and friable tissues at cesarean section in a patient diagnosed with SMDYS during pregnancy. Uncorrected cryptorchidism could lead to testicular atrophy requiring testosterone replacement therapy, or azoospermia, which had been previously reported. The authors noted that uterine contraction is smooth muscle-dependent, and pregnant women with SMDYS may not be able to generate sufficient force to deliver vaginally.

Lauer et al. (2021) performed a retrospective review of baseline and follow-up MRIs from 27 patients with a median age of 2.07 years who had SMDYS and an R179 mutation in the ACTA2 gene. Through these analyses, a pattern of progressive cerebral lesions was identified. Affected infants had characteristic white matter ischemic injury that corresponded to border zone watershed areas between cerebral artery territories. MRIs in patients older than 1.2 years demonstrated a progressively increased number of cystic-like white matter lesions, whereas white matter hyperintensities remained stable and matched areas of acute ischemic injury found in early infancy. Lauer et al. (2021) found that major cerebral artery anomalies were present in all patients and that there was a correlation between terminal internal carotid artery and cerebral artery stenosis and ischemic infarctions. There was a low incidence of hemorrhage in the patients, which was limited to microbleeds, suggesting that patients with SMDYS did not have an increased risk of intracranial bleeding. Lauer et al. (2021) proposed that characterization of the evolution of the MRI findings in patients with SMDYS may permit diagnosis in early infancy, facilitate monitoring of disease progression, and guide therapeutic interventions.

Regalado et al. (2018) reported that all by one of the heterozygous mutations identified in 33 patients with SMDYS occurred de novo.

Regalado et al. (2018) recommended that all patients with SMDYS have cardiovascular assessment every 6 to 12 months, including a transthoracic echocardiogram at each visit. They recommended magnetic resonance angiography (MRA) of the chest every year starting at age 10 years, as well as MRA of the abdomen and pelvis; upper extremity ultrasound, CT, or MRA every 12 months; and MRI of the brain or MRI of the head and neck as needed as assessed by a neurologist. Ophthalmology, growth, and nutrition and neurocognitive evaluations should be done every 12 months during childhood and adolescence, and ophthalmology throughout life. In addition, pulmonary, gastrointestinal, and urogenital assessments should be done as needed. Furthermore, the high risk of aortic dissection or rupture, stroke, and other vascular complications associated with SMDYS renders a discussion of the complications of pregnancy important prior to conception, and careful follow-up with a high-risk obstetrician and cardiologist throughout a pregnancy. Genetic counseling should be part of the ongoing care of adolescent and young adult patients to discuss concerns about inheritance, recurrence risk, and reproductive options.

In 7 unrelated patients of northern European descent with multisystemic smooth muscle dysfunction syndrome, Milewicz et al. (2010) identified heterozygosity for the same de novo missense mutation in the ACTA2 gene (R179H; 102620.0004).

Brodsky et al. (2014) identified heterozygosity for the R179H mutation in a 9-year-old boy with congenital mydriasis and prune belly syndrome with megacystis, bilateral hydroureter, and hydronephrosis requiring surgical correction. On echocardiography at age 9 years, he had severe dilatation of the aortic root and mid-ascending aorta. MRI showed massive dilatation of the intracranial arteries and tortuosity of the distal cerebral vasculature.

In 3 unrelated females with SMDYS, including 1 patient (patient E) previously reported by Milewicz et al. (2010), Yetman et al. (2015) identified heterozygosity for the R179H mutation in the ACTA2 gene. All 3 patients presented with an aneurysmal patent ductus arteriosus, leading the authors to suggest that all infants with ductal aneurysms be tested for ACTA2 mutations.

From a cohort of 7 Brazilian children with visceral myopathy phenotypes, Moreno et al. (2016) identified a 2.75-year-old girl (patient 7) with SMDYS who was heterozygous for an R179C mutation in the ACTA2 gene (102620.0008).

All 33 patients with SMDYS reviewed by Regalado et al. (2018) had ACTA2 variants at the R179 position: 1 had an R179L variant (102620.0007), 7 had the R179C variant, 1 had an R179S variant (102620.0009), and the rest had the R179H variant.