Proteus syndrome (PS) is characterized by progressive segmental or patchy overgrowth most commonly affecting the skeleton, skin, adipose, and central nervous systems. In most individuals PS has modest or no manifestations at birth, develops and progresses rapidly beginning in the toddler period, and relentlessly progresses through childhood, causing severe overgrowth and disfigurement. It is associated with a range of tumors, pulmonary complications, and a striking predisposition to deep vein thrombosis and pulmonary embolism.

Multiple synostoses syndrome is characterized by multiple joint fusions, usually commencing in the hands, conductive deafness, and characteristic facial features, including a broad, tubular-shaped nose and a thin upper vermilion. Other features include brachydactyly, hypoplastic or absent middle phalanges, radial head dislocation, and pectus carinatum (summary by Takahashi et al., 2001). Genetic Heterogeneity of Multiple Synostoses Syndrome Other forms of multiple synostoses syndrome include SYNS2 (610017), caused by mutation in the GDF5 gene (601146) on chromosome 20q11; SYNS3 (612961), caused by mutation in the FGF9 gene (600921) on chromosome 13q12; and SYNS4 (617898), caused by mutation in the GDF6 gene (601147) on chromosome 8q22.

The phenotypic spectrum of X-linked hypophosphatemia (XLH) ranges from isolated hypophosphatemia to severe lower extremity bowing and/or craniosynostosis, usually involving the sagittal suture with consequent scaphocephaly. XLH typically manifests in the first two years of life with lower extremity bowing due to the onset of weight-bearing; however, it sometimes does not manifest until adulthood, as previously unevaluated short stature. Adults may present with calcification of the tendons, ligaments, and joint capsules, joint pain, fatigue, insufficiency fractures, and impaired mobility. Persons with XLH are prone to spontaneous dental abscesses; sensorineural hearing loss has also been reported. Rarely, individuals with XLH can suffer from spinal stenosis, Chiari I malformation, syringomyelia, and/or raised intracranial pressure.

Weill-Marchesani syndrome (WMS) is a connective tissue disorder characterized by abnormalities of the lens of the eye, short stature, brachydactyly, joint stiffness, and cardiovascular defects. The ocular problems, typically recognized in childhood, include microspherophakia (small spherical lens), myopia secondary to the abnormal shape of the lens, ectopia lentis (abnormal position of the lens), and glaucoma, which can lead to blindness. Height of adult males is 142-169 cm; height of adult females is 130-157 cm. Autosomal recessive WMS cannot be distinguished from autosomal dominant WMS by clinical findings alone.

Acrodysostosis-1 (ACRDYS1) is a form of skeletal dysplasia characterized by short stature, severe brachydactyly, facial dysostosis, and nasal hypoplasia. Affected individuals often have advanced bone age and obesity. Laboratory studies show resistance to multiple hormones, including parathyroid, thyrotropin, calcitonin, growth hormone-releasing hormone, and gonadotropin (summary by Linglart et al., 2011). However, not all patients show endocrine abnormalities (Lee et al., 2012). Genetic Heterogeneity of Acrodysostosis See also ACRDYS2 (614613), caused by mutation in the PDE4D gene (600129) on chromosome 5q12.

Acrodysostosis-2 (ACRDYS2) is a rare skeletal dysplasia characterized by brachydactyly, facial dysostosis, and spinal stenosis. Many patients have intellectual disability and some have hormone resistance (summary by Michot et al., 2012 and Lee et al., 2012). For a discussion of genetic heterogeneity of acrodysostosis, see ACRDYS1 (101800).

CAGSSS, which comprises cataracts, growth hormone deficiency, sensory neuropathy, sensorineural hearing loss, and skeletal dysplasia, is an autosomal recessive multisystemic disorder with a highly variable phenotypic spectrum. Not all of these features are always present, and almost all the features may present at different times and/or become more apparent with age. The skeletal features are consistent with spondyloepimetaphyseal dysplasia (SEMD) (summary by Vona et al., 2018). One family had a distinctive presentation with infantile-onset intractable seizures and cortical abnormalities reminiscent of Leigh syndrome (see 256000). The correlation between genotype and phenotype remains unclear, but since the IARS2 gene is involved in mitochondrial function, heterogeneous manifestations can be expected (Takezawa et al., 2018).

Spondylocostal dysostosis (SCDO), defined radiographically as multiple segmentation defects of the vertebrae in combination with abnormalities of the ribs, is characterized clinically by a short trunk in proportion to height; short neck; and non-progressive mild scoliosis in most affected individuals – rarely, more significant scoliosis occurs. Respiratory function in neonates with severe disease may be compromised by reduced size of the thorax. By age two years lung growth may improve sufficiently to support relatively normal growth and development. In severely affected individuals with restricted pulmonary capacity, there is a possibility that pulmonary hypertension may eventually impact cardiac function. Males with SCDO appear to be at increased risk for inguinal hernia.

Weill-Marchesani syndrome (WMS) is a connective tissue disorder characterized by abnormalities of the lens of the eye, short stature, brachydactyly, joint stiffness, and cardiovascular defects. The ocular problems, typically recognized in childhood, include microspherophakia (small spherical lens), myopia secondary to the abnormal shape of the lens, ectopia lentis (abnormal position of the lens), and glaucoma, which can lead to blindness. Height of adult males is 142-169 cm; height of adult females is 130-157 cm. Autosomal recessive WMS cannot be distinguished from autosomal dominant WMS by clinical findings alone.

Hyper-IgE syndrome-3 with recurrent infections (HIES3) is an autosomal recessive immunologic disorder characterized by childhood onset of atopic dermatitis, skin infections particularly with Staphylococcus aureus, recurrent sinopulmonary infections, and increased serum IgE and IgG. Patients are susceptible to bacterial and fungal infections, including chronic mucocutaneous candidiasis. Immunologic workup shows impaired differentiation of CD4+ T cells into T-helper 17 cells, decreased memory B cells, and often decreased NK cells (summary by Beziat et al., 2018). For a discussion of genetic heterogeneity of hyper-IgE syndrome, see HIES1 (147060).

Noonan syndrome (NS) is characterized by characteristic facies, short stature, congenital heart defect, and developmental delay of variable degree. Other findings can include broad or webbed neck, unusual chest shape with superior pectus carinatum and inferior pectus excavatum, cryptorchidism, varied coagulation defects, lymphatic dysplasias, and ocular abnormalities. Although birth length is usually normal, final adult height approaches the lower limit of normal. Congenital heart disease occurs in 50%-80% of individuals. Pulmonary valve stenosis, often with dysplasia, is the most common heart defect and is found in 20%-50% of individuals. Hypertrophic cardiomyopathy, found in 20%-30% of individuals, may be present at birth or develop in infancy or childhood. Other structural defects include atrial and ventricular septal defects, branch pulmonary artery stenosis, and tetralogy of Fallot. Up to one fourth of affected individuals have mild intellectual disability, and language impairments in general are more common in NS than in the general population.

X-linked syndromic intellectual developmental disorder-37 (MRXS37) is a developmental disorder showing phenotypic variability and variable severity. Male mutation carriers tend to be more severely affected than female mutation carriers, some of whom may even be asymptomatic. In general, the disorder is characterized by global developmental delay with delayed walking, speech delay, impaired intellectual development that ranges from borderline low to moderate, and behavioral abnormalities, such as autism and sleeping difficulties. Many patients are able to attend mainstream schools with assistance and work under supervision. Additional more variable features include sensorineural hearing loss, ocular anomalies, feeding difficulties, dysmorphic facial features, inguinal and umbilical hernia, genitourinary defects, congenital heart defects, musculoskeletal anomalies, and endocrine dysfunction, such as hypogonadism or hyperparathyroidism (Shepherdson et al., 2024).