Hypotonia is a common finding. Around 10% of people with distal 18q- have seizures.

Dysmyelination is a common finding in people with distal 18q-, present in about 95%. Hypoplasia of the corpus callosum is also a common finding.

Recurrent otitis media is frequently associated with proximal 18q- and, in some cases, may cause conductive hearing loss. This may be resolved with the placement of PE tubes.

Feedings difficulties and problems with temperature regulation have been reported in some newborns with proximal 18q-.

In some children without “classic” holoprosencephaly, microforms of holoprosencephaly may be noted on MRI, including missing olfactory tracts and bulbs and absent or hypoplastic corpus callosum.

Children with 18p- have an increased incidence of ear infections, often requiring the placement of PE tubes.

The most common gastrointestinal abnormality is chronic constipation, though gastrointestinal reflux was also common.

Recurrent otitis media is common, and many patients required the placement of PE tubes. Small ear canals are also fairly common, but not as much as in 18q-.

Ring 18 causes a wide range of medical and developmental concerns. As discussed above, people with ring 18 can have features of both distal 18q- and 18p-. The features of distal 18q- and 18p- vary greatly because of the variability of the deletion size and breakpoint locations between people. Because ring 18 can involve unique deletions of both the p and q arms of the chromosome there is twice as much reason for the variability between individuals. This variation is also partly attributable to the incidence of mosaicism, which is relatively common in people with ring 18.

- Holoprosencephaly has been reported in some people with ring 18. This is due to the deletion of the TGIF gene on the short arm of chromosome 18 in some people with ring 18.Approximately 30-40% of people with ring 18 have a congenital heart anomaly. Septal defects are the most common type of defect reported in this population.

- Hypotonia is frequently seen in the ring 18 population. Seizures, though uncommon, have been reported in people with ring 18.

- In some children without “classic” holoprosencephaly, microforms of holoprosencephaly may be noted on MRI, including missing olfactory tracts and bulbs and absent or hypoplastic corpus callosum.

- Strabismus as well as nystagmus have both been reported in infants and children with ring 18.

- Hearing loss has been reported and may be related to ear canal atresia or stenosis.

- Umbilical and inguinal hernias have been reported in a small number of people with ring 18.

- Unilateral renal hypoplasia and aplasia have both been reported in individuals with ring 18. Hydronephrosis as well as pyelonephritis have also been reported in a few individuals. Cryptorchidism, hypospadias, and micropenis have been seen in males with ring 18, while females have been reported with hypoplastic labia.

- Foot abnormalities are common within the ring 18 population. Scoliosis as well as pectus excavatum have also been frequently reported.

- Several people with ring 18 have growth hormone deficiency. Hypothyroidism has also been reported in a minority of people.

- Cognitive ability varies; according to a literature review, the degree of impairment may fall anywhere between the mild and severe ends of the spectrum.

- Facial features of ring 18 include low-set, dysplastic ears, epicanthic folds, and hypertelorism. Micrognathia has also been reported.

Ring 18 is a genetic condition caused by a deletion of the two tips of chromosome 18 followed by the formation of a ring-shaped chromosome. It was first reported in 1964.

Singleton Merten Syndrome is an autosomal dominate genetic disorder with variable expression with an onset of symptoms during childhood.

8p23.1 duplication syndrome is a rare genetic disorder caused by a duplication of a region from human chromosome 8. This duplication syndrome has an estimated prevalence of 1 in 64,000 births and is the reciprocal of the 8p23.1 deletion syndrome. The 8p23.1 duplication is associated with a variable phenotype including one or more of speech delay, developmental delay, mild dysmorphism, with prominent forehead and arched eyebrows, and congenital heart disease (CHD).

Sugarman syndrome is the common name of autosomal recessive oral-facial-digital syndrome type III, one of ten distinct genetic disorders that involve developmental defects to the mouth.

Alternative names for this condition include: Brachydactyly of the hands and feet with duplication of the first toes, Sugarman brachydactyly and Brachydactyly with major proximal phalangeal shortening.

Clinical:

Patients often present with a history of fever of unknown origin, muscular weakness, poor development, abnormal dentition, normal serum calcium, phosphorus, and alkaline phosphatase levels. Associated clinical findings also include glaucoma, photosensitivity, heart block, foot deformities, and chronic psoriasiform skin lesions.

Radiological:

Classic radiologic findings were first described by Edward B. Singleton and David Merten in 1973.

Typical radiographic appearances include skeletal demineralization, expanded shafts of the metacarpals and phalanges with widenend medullary cavities, cardiomegaly, and intramural calcification of the proximal aorta with occasional extension into the aortic or mitral valves.

Other commonly seen radiographic findings include shallow acetabular fossa, subluxation of the femoral head, coxa valga, hypoplastic radial epiphysis, soft tissue calcifications between the radius and ulna, constriction of the proximal radial shaft, acro-osteolysis, and equinovarus foot deformities.

The phenotypic data on 11 patients indicated that cases are not always ascertained for CHD but that CHD was the most common single feature found in 6 out of 11 individuals. Developmental delay and/or learning difficulties were found in 5 out of 11 cases, but one prenatal case was developing normally at 15 months of age (Case 1,). Three other prenatal cases could not yet be reliably assessed. A variable degree of facial dysmorphism was present in 5 out of 11 individuals. Partial toe syndactyly has been found in one mother and son diad and adrenal anomalies in two probands but not in the duplicated mother of one of them. The phenotype is compatible with independent adult life with varying degrees of support.

Duplication of the GATA4 transcription factor () is believed to underlie the congenital heart disease and other genes, common to the duplication and deletion syndromes, can be regarded as candidates for the 8p23.1 duplication syndrome. These include the SOX7 transcription factor () for both CHD and developmental delay and the TNKS gene () for behavioural difficulties. The diaphragmatic hernia found in the 8p23.1 deletion syndrome has not been found in the 8p23.1 duplication syndrome to date.

The duplication may be associated with copy number changes of the adjacent olfactory receptor/defensin repeats (ORDRs) that predispose to the 8p23.1 deletion and duplication syndromes. High total copy numbers of these repeats have been associated with predisposition to psoriasis and low copy number with predisposition to Crohn's disease.

The Wassel classification is used to categorise radial polydactyly, based upon the most proximal level of skeletal duplication.

Lenz–Majewski syndrome is a skin condition characterized by hyperostosis, craniodiaphyseal dysplasia, dwarfism, cutis laxa, proximal symphalangism, syndactyly, brachydactyly, mental retardation, enamel hypoplasia, and hypertelorism.

In 2013, whole-exome sequencing showed that a missense mutation resulting in overactive phosphatidylserine synthase 1 was the cause of LMS, making it the first known human disease to be caused by disrupted phosphatidylserine metabolism. The researchers suggested a link between the condition and bone metabolism.

Bart–Pumphrey syndrome (also known as "Palmoplantar keratoderma with knuckle pads and leukonychia and deafness") is a cutaneous condition characterized by hyperkeratoses (knuckle pads) over the metacarpophalangeal, proximal and distal interphalangeal joints.

It was characterized in 1967.

It can be associated with GJB2.

Limb girdle syndrome is a term to describe several distinct medical conditions including polymyositis, myopathy associated with endocrine disease, metabolic myopathy, drug-induced myopathy and limb-girdle muscular dystrophy.

Limb girdle syndrome is weakness located and concentrated around the proximal limb muscles. There are many causes, manifestations and treatments.

Proximal femoral focal deficiency (PFFD), also known as Congenital Femoral Deficiency (CFD), is a rare, non-hereditary birth defect that affects the pelvis, particularly the hip bone, and the proximal femur. The disorder may affect one side or both, with the hip being deformed and the leg shortened.

It is commonly linked with the absence or shortening of a leg bone (fibular hemimelia) and the absence of a kneecap. Other linked birth defects include the dislocation or instability of the joint between the femur and the kneecap, a shortened tibia or fibula, and foot deformities.

There are typically four classes (or "types") of PFFD, ranging from class A to class D, as detailed by Aitken.

Hypospadias is a congenital disorder of the urethra where the urinary opening is not at the usual location on the head of the penis. It is the second-most common birth abnormality of the male reproductive system, affecting about one of every 250 males at birth. In roughly 90% of cases, the opening (meatus) is on or near the head of the penis (glans), referred to as distal hypospadias, while the remainder have proximal hypospadias with a meatus near or within the scrotum. Shiny tissue seen extending from the meatus to the tip of the glans, which would have made the urinary channel, is referred to as the urethral plate.

In most cases, the foreskin is also underdeveloped and does not wrap completely around the penis, leaving the underside of the glans penis uncovered. Also, a downward bending of the penis, commonly referred to as chordee, may occur. This is found in 10% of distal hypospadias and 50% of proximal hypospadias at the time of surgery. The scrotum may be higher than usual to either side of the penis, called penoscrotal transposition, adding to the abnormal overall appearance.

Hypospadias is thought to result from failure of the urinary channel to completely tubularize to the end of the penis; the cause is not known. Most often, it is the only abnormal finding, although in about 10% of cases, hypospadias may be part of a syndrome with multiple abnormalities.

The most common associated defect is an undescended testicle, which has been reported in around 3% of infants with distal hypospadias and 10% of those having proximal hypospadias. The combination of hypospadias and an undescended testicle sometimes indicates a disorder of sexual differentiation, and so additional testing may be recommended. Otherwise no blood tests or X-rays are routinely needed in newborns with hypospadias.

Hypospadias can be a symptom or indication of an intersex condition but the presence of hypospadias alone is not enough to classify as intersex. In most cases, hypospadias is not associated with any condition.

Hypospadias is usually diagnosed in the newborn nursery by the characteristic appearance of the penis. The urinary opening (“meatus”) is lower than normal, and most children have only partial development of the foreskin, lacking the normal covering for the glans on the underside. The abnormal “hooded” foreskin calls attention to the condition. However, not all newborns with partial foreskin development have hypospadias, as some have a normal urinary opening with a hooded foreskin, which is called “chordee without hypospadias”.

Megameatus with intact prepuce variant of hypospadias occurs when the foreskin is normal and the hypospadias is concealed. The condition is discovered during newborn circumcision or later in childhood when the foreskin begins to retract. A newborn with normal-appearing foreskin and a straight penis who is discovered to have hypospadias after a circumcision was started can have circumcision completed without worry for jeopardizing future hypospadias repair. Hypospadias is almost never discovered after a circumcision.

Myopathic gait (or waddling gait) is a form of gait abnormality.

The "waddling" is due to the weakness of the proximal muscles of the pelvic girdle.

The patient uses circumduction to compensate for gluteal weakness.

Conditions associated with a myopathic gait include pregnancy, congenital hip dysplasia, muscular dystrophies and spinal muscular atrophy

Synostosis (plural: synostoses) is fusion of two bones. It can be normal in puberty, fusion of the epiphysis, or abnormal. When synostosis is abnormal it is a type of dysostosis.

Examples of synostoses include:

- craniosynostosis – an abnormal fusion of two or more cranial bones;

- radioulnar synostosis – the abnormal fusion of the radius and ulna bones of the forearm;

- tarsal coalition – a failure to separately form all seven bones of the tarsus (the hind part of the foot) resulting in an amalgamation of two bones; and

- syndactyly – the abnormal fusion of neighboring digits.

Synostosis within joints can cause ankylosis.