Wiedemann-Rautenstrauch syndrome (WDRTS) is a rare autosomal recessive neonatal progeroid disorder characterized by intrauterine growth retardation, failure to thrive, short stature, a progeroid appearance, hypotonia, and variable mental impairment (summary by Toriello, 1990). Average survival in WDRTS is 7 months, although survival into the third decade of life has been reported (Akawi et al., 2013).

A rare chromosomal anomaly with characteristics of psychomotor developmental delay, facial dysmorphism (trigonocephaly, midface hypoplasia, upslanting palpebral fissures, dysplastic small ears, flat nasal bridge with anteverted nostrils and long philtrum, micrognathia, choanal atresia, short neck), single umbilical artery, omphalocele, inguinal or umbilical hernia, genital abnormalities (hypospadia, cryptorchidism), muscular hypotonia and scoliosis.

Nicolaides-Baraitser syndrome (NCBRS) is characterized by sparse scalp hair, prominence of the inter-phalangeal joints and distal phalanges due to decreased subcutaneous fat, characteristic coarse facial features, microcephaly, seizures, and developmental delay / intellectual disability. Seizures are of various types and can be difficult to manage. Developmental delay / intellectual disability (ID) is severe in nearly a half, moderate in a third, and mild in the remainder. Nearly a third never develop speech or language skills.

Carnitine palmitoyltransferase II (CPT II) deficiency is a disorder of long-chain fatty-acid oxidation. The three clinical presentations are lethal neonatal form, severe infantile hepatocardiomuscular form, and myopathic form (which is usually mild and can manifest from infancy to adulthood). While the former two are severe multisystemic diseases characterized by liver failure with hypoketotic hypoglycemia, cardiomyopathy, seizures, and early death, the latter is characterized by exercise-induced muscle pain and weakness, sometimes associated with myoglobinuria. The myopathic form of CPT II deficiency is the most common disorder of lipid metabolism affecting skeletal muscle and the most frequent cause of hereditary myoglobinuria. Males are more likely to be affected than females.

Siderius-type syndromic intellectual developmental disorder (MRXSSD) is an X-linked disorder in which affected males have mildly impaired intellectual development, mild dysmorphic features, and bilateral or unilateral cleft lip/palate (summary by Koivisto et al., 2007).

A rare genetic developmental defect during embryogenesis disorder with characteristics of craniofacial dysmorphism (including brachycephaly, prominent forehead, sparse lateral eyebrows, severe hypertelorism, upslanting palpebral fissures, epicanthal folds, protruding ears, broad nasal bridge, pointed nasal tip, flat philtrum, anteverted nostrils, large mouth, thin upper vermilion border, highly arched palate and mild micrognathia) associated with osteopenia leading to repeated long bone fractures, severe myopia, mild to moderate sensorineural or mixed hearing loss, enamel hypoplasia, sloping shoulders and mild intellectual disability. There is evidence the disease can be caused by homozygous mutation in the IRX5 gene on chromosome 16q11.2.

17q23.1q23.2 microdeletion syndrome is a recently described syndrome characterized by developmental delay, microcephaly, short stature, heart defects and limb abnormalities.

The 17q12 recurrent deletion syndrome is characterized by variable combinations of the three following findings: structural or functional abnormalities of the kidney and urinary tract, maturity-onset diabetes of the young type 5 (MODY5), and neurodevelopmental or neuropsychiatric disorders (e.g., developmental delay, intellectual disability, autism spectrum disorder, schizophrenia, anxiety, and bipolar disorder). Using a method of data analysis that avoids ascertainment bias, the authors determined that multicystic kidneys and other structural and functional kidney anomalies occur in 85% to 90% of affected individuals, MODY5 in approximately 40%, and some degree of developmental delay or learning disability in approximately 50%. MODY5 is most often diagnosed before age 25 years (range: age 10-50 years).

GAND syndrome is a neurodevelopmental syndrome characterized by global developmental delay apparent from infancy, with motor delay and moderate to severely impaired intellectual development. Most patients have poor speech acquisition, especially expressive language development, and may manifest signs of speech apraxia. Affected individuals have hypotonia and feeding difficulties in infancy, as well as common dysmorphic features, such as macrocephaly, frontal bossing, hypertelorism, deep-set eyes, posteriorly rotated ears, and elongated wide nose with prominent nasal tip. More variable features may include seizures, cardiac abnormalities, and nonspecific findings on brain imaging (summary by Shieh et al., 2020).

A rare, genetic, parenchymal hepatic disease characterized by acute liver failure, that occurs in the first year of life, which manifests with failure to thrive, hypotonia, moderate global developmental delay, seizures, abnormal liver function tests, microcytic anemia and elevated serum lactate. Other associated features include hepatosteatosis and fibrosis, abnormal brain morphology, and renal tubulopathy. Minor illness exacerbates deterioration of liver failure.

PDE4D haploinsufficiency syndrome is a rare syndromic intellectual disability characterized by developmental delay, intellectual disability, low body mass index, long arms, fingers and toes, prominent nose and small chin.

Spondyloocular syndrome (SOS) is an autosomal recessive disorder characterized by platyspondyly, bone fragility, cataract, retinal detachment, hearing impairment, cardiac defects, and facial dysmorphism (Schmidt et al., 2001; Munns et al., 2015).

Ehlers-Danlos syndrome spondylodysplastic type 1 (EDSSPD1) is characterized by short stature, developmental anomalies of the forearm bones and elbow, and bowing of extremities, in addition to the classic stigmata of Ehlers-Danlos syndrome, including joint laxity, skin hyperextensibility, and poor wound healing. Significant developmental delay is not a consistent feature (Guo et al., 2013). Genetic Heterogeneity of Ehlers-Danlos Syndrome, Spondylodysplastic Type See EDSSPD2 (615349), caused by mutation in the B3GALT6 gene (615291), and EDSSPD3 (612350), caused by mutation in the SLC39A13 gene (608735).

IDDCDF is an autosomal recessive syndromic neurodevelopmental disorder characterized by globally impaired development with intellectual disability and speech delay, congenital cardiac malformations, and dysmorphic facial features. Additional features, such as distal skeletal anomalies, may also be observed (Stephen et al., 2018).

VISS syndrome is a generalized connective tissue disorder characterized by early-onset thoracic aortic aneurysm and other connective tissue findings, such as aneurysm and tortuosity of other arteries, joint hypermobility, skin laxity, and hernias, as well as craniofacial dysmorphic features, structural cardiac defects, skeletal anomalies, and motor developmental delay (Van Gucht et al., 2021). Immune dysregulation has been observed in some patients (Ziegler et al., 2021).

Short stature of the Dauber-Argente type (SSDA) is characterized by progressive postnatal growth failure, moderate microcephaly, thin long bones, and mildly decreased bone density. Patients have elevated circulating levels of total IGF1 (147440) due to impaired proteolysis of IGFBP3 (146732) and IGFBP5 (146734), resulting in reduced free IGF1 (Dauber et al., 2016).

Boudin-Mortier syndrome (BOMOS) is characterized by tall stature, arachnodactyly, disproportionately elongated great toes, and multiple extra epiphyses. Some patients also show joint hypermobility and dilation of the aortic root (Boudin et al., 2018). Mutation in the NPR2 gene (108961) results in a similar phenotype of increased stature and elongation of the digits, particularly of the great toes, with multiple extra epiphyses (epiphyseal chondrodysplasia, Miura type; 615923).