Dyggve-Melchior-Clausen disease (DMC) is an autosomal recessive disorder characterized by progressive spondyloepimetaphyseal dysplasia and impaired intellectual development. Short-trunk dwarfism and microcephaly are present, and specific radiologic appearances most likely reflect abnormalities of the growth plates, including platyspondyly with notched end plates, metaphyseal irregularities, laterally displaced capital femoral epiphyses, and small iliac wings with lacy iliac crests (summary by El Ghouzzi et al., 2003).

Spinocerebellar ataxia-29 (SCA29) is an autosomal dominant neurologic disorder characterized by onset in infancy of delayed motor development and mild cognitive delay. Affected individuals develop a very slowly progressive or nonprogressive gait and limb ataxia associated with cerebellar atrophy on brain imaging. Additional variable features include nystagmus, dysarthria, and tremor (summary by Huang et al., 2012). For a general discussion of autosomal dominant spinocerebellar ataxia, see SCA1 (164400).

Three M syndrome is characterized by severe pre- and postnatal growth deficiency (final height 5-6 SD below the mean; i.e., 120-130 cm), characteristic facies, and normal intelligence. Additional features of three M syndrome include short broad neck, prominent trapezii, deformed sternum, short thorax, square shoulders, winged scapulae, hyperlordosis, short fifth fingers, prominent heels, and loose joints. Males with three M syndrome have hypogonadism and occasionally hypospadias.

Three M syndrome is characterized by severe pre- and postnatal growth deficiency (final height 5-6 SD below the mean; i.e., 120-130 cm), characteristic facies, and normal intelligence. Additional features of three M syndrome include short broad neck, prominent trapezii, deformed sternum, short thorax, square shoulders, winged scapulae, hyperlordosis, short fifth fingers, prominent heels, and loose joints. Males with three M syndrome have hypogonadism and occasionally hypospadias.

Smith-McCort dysplasia is a rare autosomal recessive osteochondrodysplasia characterized by short trunk dwarfism with a barrel-shaped chest, rhizomelic limb shortening, and specific radiologic features including marked platyspondyly with double-humped end-plates, kyphoscoliosis, metaphyseal irregularities, laterally displaced capital femoral epiphyses, and small pelvis with a lace-like appearance of iliac crests. These clinical and radiologic features are also common to Dyggve-Melchior-Clausen syndrome (DMC; 223800), which is distinguished from SMC by the additional feature of mental retardation (summary by Dupuis et al., 2013). For a discussion of genetic heterogeneity of Smith-McCort dysplasia, see SMC1 (607326).