Hypertrophic cardiomyopathy combined with renal and adrenal aplasia in a male with Noonan syndrome from RAF1 variant

Abstract

Noonan syndrome (NS) is a hereditary multisystem disorder caused by variants in different genes, resulting in a similar clinical presentation with an estimated prevalence of 1/1000–1/2500.¹ It is an orphan disease with multisystem involvement, characterized by distinctive facial features, developmental delays, learning difficulties, short stature, congenital heart disease, kidney abnormalities, lymphatic malformation, coagulation abnormalities and skeletal deformities.² The pathogenesis of NS is associated with the upregulation of the crucial cell signalling pathway RAS-MAPK. RAF1 variants associated NS are closely linked to cardiac abnormalities, especially hypertrophic cardiomyopathy (HCM), leading to poor prognosis and early mortality.^{3, 4} HCM combined with aplasia of unilateral kidney and adrenal gland associated with NS has been rarely reported in literatures. We described these phenotypic features in a male patient presenting with missense heterozygote RAF1 mutation.

A 21-year-old young male presented to coronary care unit with sudden onset of dyspnoea and palpitations for 6 h. When he was a 1-year-old infant, he was taken to the hospital due to respiratory distress and lower limb oedema. The doctors found that his ventricles were abnormally thickened, but the cause was unknown. As he grew up, he was shorter and lighter than his peers. He was prone to dyspnoea during physical exertion such as running, cycling and so on. It was his first sudden episode of palpitations, followed by dyspnoea, prompting him to seek medical attention. He was born from a nonconsanguineous marriage and had a normal perinatal period. There were no other significant relevant histories, such as hypertension, diabetes, hyperthyroidism, smoking or drinking. His elder sister suffered from systemic lupus erythematosus (SLE). His parents and other siblings were in good health.

His height was 145 cm and weight was 36 kg, resulting in a calculated BMI of 17 kg/m². He was breathing quickly (25 breaths per minute) with a blood pressure of 124/56 mmHg and oxygen saturation 95%. He had characteristic facial traits of macrocephaly, micrognathia, bilateral ptosis, epicanthal folds, downward slanting palpebral fissures and bulbous nasal tip. The jugular veins were distended. His chest deformity presented a pectus carinatum shape. There were slight crackling sounds in bilateral lower lung. His heart rate was 150 b.p.m. while pulse rate was 135 b.p.m. with irregular rhythm. A grade 3/6 systolic murmur was audible at the 3rd intercostal space adjacent to his sternum. There was no oedema in his lower limbs.

Table 1 illustrates laboratory findings for the patient at presentation. N terminal pro brain natriuretic peptide (NT-proBNP) and troponin I were elevated. Urinalyses indicated intermittent proteinuria. Parathyroid hormone was elevated. Serum creatinine, estimated glomerular filtration rate (eGFR) and electrolyte indicators were normal. Blood gas analysis revealed no hypoxaemia or carbon dioxide retention. Testosterone, luteinizing hormone (LH) and prolactin were elevated. Insulin-like growth factor-1 (IGF-1) and growth hormone did not decrease. Adrenocorticotropic hormone (ACTH) secretion, cortisol circadian rhythm, hormone levels of thyroid gland and follicle stimulating hormone (FSH) were normal. White blood cell counts and serum uric acid were elevated.

His electrocardiogram indicated rapid atrial fibrillation (AF) and incomplete right bundle branch block. Bedside chest X-ray suggested marked cardiac enlargement.

His echocardiogram showed biventricular hypertrophy with enlargement of bilateral atrium (Table 2, Figure 1A,B). The left ventricle was severely hypertrophic with a spindle-shaped thickening in the middle of interventricular septum (41.5 mm) (Table 2, Figure 1A,B). There were no left ventricular outflow tract obstruction (LVOTO), systolic anterior motion (SAM) or aortic stenosis (Table 2, Figure 1D,E). But there was a midventricular obstruction. A multicoloured mosaic of blood flow was observed during systole at the mid-region of left ventricle proximate to left ventricular outflow tract (LVOT) (Figure 1C). The peak velocity of mid-ventricle was 247.28 cm/s, and peak gradient was 24.46 mmHg in basal condition (Table 2 and Figure 1F); however, velocity and peak pressure gradient were significantly increased by Valsalva test (305.04 cm/s, 37.22 mmHg) (Table 2 and Figure 1G). Left ventricular ejection fraction (LVEF) was 67% (Table 2). The echocardiography showed a marked right ventricular hypertrophy with right ventricular outflow tract (RVOT) obstruction (peak velocity: 458.01 cm/s, peak gradient: 83.91 mmHg) (Table 2, Figure 1A,H–J). Pulmonary artery was dilated (34.9 mm). Pulmonary stenosis was not detected (Table 2 and Figure 1K).

Computed tomography (CT) revealed that the right adrenal gland and kidney were not observed. A small cystic lesion was seen in the right renal area (Figure 2). The left adrenal gland and kidney showed compensatory enlargement.

Ultrasound examination reveals that bilateral testicle and epididymides are of normal size and shape.

The patient presented with paroxysmal AF complicated by heart failure (HF). Intravenous amiodarone was administered. The patient successfully converted to sinus rhythm. The symptoms gradually improved. The patient received treatment with furosemide, spironolactone, dapagliflozin and rivaroxaban.

Whole-exome sequencing showed a pathogenic heterozygous missense mutation NM_002880.4(RAF1):c.770C > T (p.Ser257Leu). Genetic testing showed the presence of a pathogenic RAF1 mutation associated with NS. The variant was absent in his parents.

Four months after discharge, the patient experienced an influenza B virus infection with transient worsening of heart failure. Following antiviral treatment, the symptoms stabilized quickly. During nearly 2 months follow-up, the patient was able to perform daily activities and work without significant dyspnoea or palpitations.

This report described that a patient presented with HCM, aplasia of right kidney and right adrenal gland due to missense mutation RAF1. NS due to RAF1 gene is inherited as an autosomal dominant trait. This report confirms the presence of multisystem pathological phenotypes in patients with NS related to RAF1 variants.

The RAF1 protein is a member of a small family of serine–threonine kinases that function as RAS effectors.⁵ The RAF1 gene encodes a protein consisting of three distinct functional domains, referred to as conserved regions 1, 2 and 3 (CR1, CR2 and CR3). Mutations impact the grouping of amino acids in three distinct areas of the protein. The initial cluster includes the N-terminal consensus sequence recognized by 14-3-3 proteins or neighbouring amino acids located within the CR2 region. It is important to highlight that the invariant residues within this motif, namely, Arg256, Ser257, Ser259 and Pro261, have all been identified as mutated. Approximately 70% of the overall defects in RAF1 are attributed to mutations that lead to substitutions of amino acids in this specific region.⁵ The pathogenic variant NS gene of the patient is located at RAF1(NM 002880.4), genomic position: Chr3: g.12645699, cDNA change: c.770C > T, amino acid change: p.Ser257Leu. It is a missense mutation. The amino acid alterations Ser257Leu, which influences the 14-3-3 binding motif or the protein's C-terminus, leads to heightened kinase activity and a greater activation of the MAPK cascade relative to the wild-type protein.⁶ In patients with NS, the mutations that cause alterations in the CR2 domain of RAF1 have been identified in individuals suffering from HCM.⁷ Elevated RAS signalling is associated with the pathological hypertrophy of cardiomyocytes. The phenotype of HCM consists of LVOTO, mitral valve abnormalities, diastolic dysfunction, myocardial ischemia, arrhythmias, metabolic and energetic abnormalities, and potentially autonomic dysfunction.^{8, 9} Even in the absence of hypertrophy, this cardiomyopathy could be manifested solely as abnormalities in mitral valve (elongated mitral leaflets, thick leaflets, displacement of papillary muscles and systolic anterior motion).^{10, 11}The patient has exhibited symptoms of HF since infancy, with echocardiography revealing ventricular hypertrophy. He was admitted due to HF and AF. The echocardiogram demonstrated significant bilateral ventricular hypertrophy. There was obstruction in left ventricle mid-region and RVOT. Based on his facial features, multimodal imaging and genetic testing, a diagnosis of NS was established.

The patient exhibits aplasia of right kidney. Renal anomalies have been reported in approximately 10%–11% of NS cases, although they generally hold little clinical importance.^{1, 12} Common findings include the presence of a single kidney and duplication of the urinary collecting system. However, the presence of unilateral renal and adrenal aplasia is rarely reported in patients with NS. It was reported that a term male neonate suffered from pulmonary vasculitis and a horseshoe kidney with c.184 T > G (p.Tyr62Asp) pathogenic variant in PTPN11.¹³ Tejani et al. present a case of an infant exhibiting characteristics of NS, who also demonstrated early signs of significant renal failure resulting from renal dysplasia associated with cystic disease.¹⁴ The serum creatinine and eGFR of our patient were within the normal range. But the patient presents with intermittent proteinuria. His follow-up should be continued over the long term.

The patient has right adrenal aplasia. Based on the imaging examinations, there is no evidence of cryptorchidism or gonadal dysgenesis. Following the assessment of sex hormones and corticosteroids, no significant changes have been observed except for the mild elevation of LH and prolactin. The earliest stages of adrenal gland development may be influenced by various transcription factors (such as SF1 [NR5A1] and DAX1 [NROB1]), related regulatory factors, signalling molecules, extracellular matrix proteins and telomerase activity regulators.¹⁵ Nevertheless, there are no reported associations between adrenal gland development and RAF1. RAF1 may influence the development of adrenal glands by modulating certain cellular signalling pathways mentioned above.¹⁶

Clinical red flags for NS are growth retardation, craniofacial features and congenital heart defects.¹⁷ The main craniofacial features are ocular hypertelorism, down-slanting palpebral fissures, ptosis and low-set posteriorly rotated ears with a thickened helix.¹⁷ The cardiovascular defects are associated with pulmonary valve stenosis, HCM, mitral valve dysplasia, atrial septal defect, ventricular septal defect, atrioventricular septal defect and aortic coarctation.^{17, 18} Electrocardiograms display wide QRS complexes with a predominantly negative pattern in the left precordial leads.¹⁷ Chest deformities consist of pectus carinatum superiorly and pectus excavatum inferiorly.¹⁷ Other features of NS were mental retardation, cryptorchidism, urinary tract malformations, bleeding disorders, variable predisposition to certain cancers and lymphatic dysplasia.^{17, 18}

The patient currently presents with HCM, right kidney aplasia and adrenal gland aplasia, which may represent novel phenotypes associated with RAF1 related NS. It is essential for physicians to monitor the cardiac, renal and adrenal parameters during follow-up. This report contributes to the growing body of literature on the clinical spectrum of NS. There was a potential relationship between RAF1 and the development of heart, kidney and adrenal gland. This warrants further exploration and research into the pathogenic mechanisms involved.

This work was supported by the fifth batch of Shantou Medical and Health Science and Technology Plan Project in 2019 (financial fund support) (No. Shantou Government Technology [2019] 106-20).

The authors declare no conflicts of interest.